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<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">
<title>风酥糖</title>
<subtitle>fetasty</subtitle>
<link href="https://fetasty.github.io/atom.xml" rel="self"/>
<link href="https://fetasty.github.io/"/>
<updated>2024-02-26T03:30:17.855Z</updated>
<id>https://fetasty.github.io/</id>
<author>
<name>fetasty</name>
</author>
<generator uri="https://hexo.io/">Hexo</generator>
<entry>
<title>scapy 简单使用</title>
<link href="https://fetasty.github.io/posts/fff1101d/"/>
<id>https://fetasty.github.io/posts/fff1101d/</id>
<published>2024-02-26T03:26:57.000Z</published>
<updated>2024-02-26T03:30:17.855Z</updated>
<content type="html"><![CDATA[<p>Scapy 是一个强大的数据包处理工具，可以轻松的按照层次构建网络包，比如这样</p><figure class="highlight python"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">packet = Ether()/IP(dst=<span class="string">"192.168.0.1"</span>)/TCP(dport=<span class="number">80</span>)/<span class="string">b'data'</span></span><br></pre></td></tr></tbody></table></figure><span id="more"></span><p>可以轻松的获取某一层的内容</p><figure class="highlight python"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">if</span> packet.haslayer(Ether):</span><br><span class="line"> packet.getlayer(Ether).show()</span><br><span class="line"></span><br><span class="line"><span class="keyword">if</span> packet.haslayer(Raw):</span><br><span class="line"> packet.getlayer(Raw).show()</span><br><span class="line"></span><br><span class="line">packet.original <span class="comment"># 包的原始二进制bytes</span></span><br><span class="line">packet.getlayer(TCP).original <span class="comment"># 获取包的TCP层的二进制bytes</span></span><br></pre></td></tr></tbody></table></figure><p>可以读取 wireshark 的捕获文件</p><figure class="highlight python"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">packets = rdpcap(<span class="string">'wireshark_capture.pcap'</span>)</span><br><span class="line"><span class="keyword">for</span> packet <span class="keyword">in</span> packets:</span><br><span class="line"> <span class="comment"># pass</span></span><br><span class="line">packets[<span class="number">0</span>].payload.show()</span><br></pre></td></tr></tbody></table></figure><p>可以在第 2 层或者第 3 层发送数据包，分别使用 <code>sendp</code> 或者 <code>send</code></p><p>也可以使用 scapy 来重播 wireshark 捕获的包</p><figure class="highlight plaintext"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">pip install scapy</span><br></pre></td></tr></tbody></table></figure><figure class="highlight python"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">from</span> scapy.<span class="built_in">all</span> <span class="keyword">import</span> *</span><br><span class="line"><span class="keyword">import</span> socket</span><br><span class="line"></span><br><span class="line"><span class="comment"># 创建TCP服务器</span></span><br><span class="line">server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)</span><br><span class="line">server_socket.bind((<span class="string">'192.168.10.225'</span>, <span class="number">8555</span>))</span><br><span class="line">server_socket.listen(<span class="number">1</span>)</span><br><span class="line"></span><br><span class="line"><span class="built_in">print</span>(<span class="string">"服务器已启动，等待客户端连接..."</span>)</span><br><span class="line"></span><br><span class="line"><span class="comment"># 接受客户端连接</span></span><br><span class="line">client_socket, client_address = server_socket.accept()</span><br><span class="line"><span class="built_in">print</span>(<span class="string">"客户端已连接："</span>, client_address)</span><br><span class="line"></span><br><span class="line"><span class="comment"># 网口</span></span><br><span class="line">select_iface = <span class="literal">None</span></span><br><span class="line"></span><br><span class="line"><span class="built_in">print</span>(<span class="string">'-'</span> * <span class="number">10</span>)</span><br><span class="line"><span class="keyword">for</span> inter <span class="keyword">in</span> conf.ifaces:</span><br><span class="line"> iface: NetworkInterface = conf.ifaces[inter]</span><br><span class="line"> <span class="built_in">print</span>(iface.name, iface.network_name)</span><br><span class="line"> <span class="keyword">if</span> iface.name == <span class="string">'环回测试'</span>:</span><br><span class="line"> select_iface = iface</span><br><span class="line"> <span class="built_in">print</span>(iface.ips)</span><br><span class="line"> <span class="built_in">print</span>(<span class="string">'192.168.1.2'</span> <span class="keyword">in</span> iface.ips[<span class="number">4</span>]) <span class="comment"># 也可以以这个作为判断条件, 寻找正确的网口</span></span><br><span class="line"></span><br><span class="line"><span class="comment"># 读取pcap文件</span></span><br><span class="line">packets: PacketList = rdpcap(<span class="string">'225to121_targets.pcapng'</span>)</span><br><span class="line"></span><br><span class="line"><span class="keyword">for</span> packet <span class="keyword">in</span> packets:</span><br><span class="line"> p: Packet = packet</span><br><span class="line"> <span class="keyword">if</span> p.haslayer(Raw):</span><br><span class="line"> <span class="comment"># 重播数据包</span></span><br><span class="line"> raw_layer = p.getlayer(Raw)</span><br><span class="line"> sendp(raw_layer.original, inter=<span class="number">0.5</span>, socket=client_socket)</span><br><span class="line"> <span class="built_in">print</span>(<span class="string">f"send: <span class="subst">{raw_layer.original.<span class="built_in">hex</span>()}</span>"</span>)</span><br><span class="line"></span><br><span class="line"><span class="comment"># 关闭连接</span></span><br><span class="line">client_socket.close()</span><br><span class="line">server_socket.close()</span><br></pre></td></tr></tbody></table></figure><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kity.min.js"></script><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kityminder.core.min.js"></script><script defer="true" type="text/javascript" src="https://unpkg.com/[email protected]/dist/mindmap.min.js"></script><link rel="stylesheet" type="text/css" href="https://unpkg.com/[email protected]/dist/mindmap.min.css">]]></content>
<summary type="html"><p>Scapy 是一个强大的数据包处理工具，可以轻松的按照层次构建网络包，
比如这样</p>
<figure class="highlight python"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">packet = Ether()/IP(dst=<span class="string">"192.168.0.1"</span>)/TCP(dport=<span class="number">80</span>)/<span class="string">b'data'</span></span><br></pre></td></tr></tbody></table></figure></summary>
<category term="计算机基础" scheme="https://fetasty.github.io/categories/computer-science/"/>
<category term="计算机基础" scheme="https://fetasty.github.io/tags/computer-science/"/>
<category term="网络" scheme="https://fetasty.github.io/tags/network/"/>
</entry>
<entry>
<title>Wireshark 使用说明</title>
<link href="https://fetasty.github.io/posts/8eb85eb3/"/>
<id>https://fetasty.github.io/posts/8eb85eb3/</id>
<published>2024-02-26T03:08:52.000Z</published>
<updated>2024-02-26T03:13:30.511Z</updated>
<content type="html"><![CDATA[<h2 id="理解网络层次">理解网络层次</h2><p>OSI 五层协议</p><ul><li><p>物理层：一般是基于电信号进行 bit 流传输</p></li><li><p><strong>数据链路层</strong>: 定义 bit 信号分组方式，常见的协议是以太网协议 (Ethernet)</p><p>Ethernet 数据帧 [帧头，数据，帧尾]</p></li><li><p><strong> 网络层</strong>: 划分广播域 / 子网，一般网络层都是 IP 协议</p><p>IP 数据帧 [报头，数据]</p></li><li><p><strong> 传输层</strong>: 建立端口到端口的通信，常见传输层协议有 TCP/UDP</p><p>TCP 基于连接，提供可靠传输，面向字节流，三次握手 / 四次挥手(创建 / 断开连接), 粘包 / 拆包，timewait, 报文头长，总体传输慢，窗口，拥塞控制</p><p>UDP 无连接，尽可能快，不可靠传输，面向报文，过长报文会被分片</p></li><li><p><strong>应用层</strong></p></li></ul><img data-src="/posts/8eb85eb3/network_layers.png" class=""><p></p><p>使用 Wireshark 分析数据包时，一般关注的是后面三层，每层的报文头中都包含了特定信息，在数据层存放更上层的数据</p><span id="more"></span><p></p><h2 id="实际报文分析">实际报文分析</h2><p>我们看一个实际的 TCP 报文</p><figure class="highlight plaintext"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br></pre></td><td class="code"><pre><span class="line">###[ Ethernet ]###</span><br><span class="line"> dst = e0:73:e7:6f:b0:1b</span><br><span class="line"> src = 00:20:22:01:05:b6</span><br><span class="line"> type = IPv4</span><br><span class="line">###[ IP ]###</span><br><span class="line"> version = 4</span><br><span class="line"> ihl = 5</span><br><span class="line"> tos = 0x0</span><br><span class="line"> len = 132</span><br><span class="line"> id = 48263</span><br><span class="line"> flags = DF</span><br><span class="line"> frag = 0</span><br><span class="line"> ttl = 128</span><br><span class="line"> proto = tcp</span><br><span class="line"> chksum = 0xa741</span><br><span class="line"> src = 192.168.10.225</span><br><span class="line"> dst = 192.168.10.121</span><br><span class="line"> \options \</span><br><span class="line">###[ TCP ]###</span><br><span class="line"> sport = 8555</span><br><span class="line"> dport = 50283</span><br><span class="line"> seq = 739877280</span><br><span class="line"> ack = 3545067859</span><br><span class="line"> dataofs = 5</span><br><span class="line"> reserved = 0</span><br><span class="line"> flags = PA</span><br><span class="line"> window = 40942</span><br><span class="line"> chksum = 0xd82f</span><br><span class="line"> urgptr = 0</span><br><span class="line"> options = []</span><br><span class="line">###[ Raw ]###</span><br><span class="line"> load = '\\xc9\x00\x00\x00\\xf9\x00\x00\x00\\xbc\x14\\xa8e\x02\x00\x00\x00H\x00\x00\x00\\x80\\xd85\\\x01\x00\x00\x00\\x80\\xd85\\\x01\x00\x00\x00\\x80\\x96\\x98\x00\\xef\x03\x00\x00\x00\x00\x00\x00\x00\\xa0Z@33333\\xf3b@\\xbc\x14\\xa8e\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x06\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'</span><br></pre></td></tr></tbody></table></figure><ul><li><p>以太网层 (Ethernet) 中最重要的信息</p><ul><li>源 MAC 地址</li><li>目的 MAC 地址</li><li>上层协议类型</li></ul></li><li><p>网络层 (IP)</p><ul><li>源 IP 地址</li><li>目的 IP 地址</li><li>版本，长度，标志位，上层协议类型 等</li></ul></li><li><p>传输层 (TCP)</p><ul><li>源端口</li><li>目的端口</li><li>长度，标志位，序列号 / 应答号 等</li></ul></li><li><p>用户数据 (示例中的传输层数据不是像 HTTP 一样普通的传输层协议报文，可能是自定义的协议报文)</p></li></ul><p></p><h2 id="选择正确的网口">选择正确的网口</h2><p>使用 Wireshark 抓包，首先需要选择正确的网络接口，如果目的数据包的源 IP 或者目的 IP 在某个网络接口上，就选择该网络接口</p><p>一般来说，名称中包含 "以太网" 的接口是通过网线连接的网口；包含 "WLAN" 的是无线网络的网口</p><p>Windows 上可以使用 <code>ipconfig /all</code> 来查看网口信息，确定要使用的网口</p><p>或者鼠标指向对应的网口，在 Tooltip 中查看网口配置的 IP 信息</p><p></p><h2 id="网络包过滤">网络包过滤</h2><p>开始捕获后一般会发现一个网口上的报文数量非常庞大，不过滤根本看不清楚</p><p>此时我们就需要用到上述网络层次相关知识</p><ul><li><p>网络层过滤 (IP 协议信息过滤)</p><p>IP 协议包含了源 IP 地址和目的 IP 地址，这也是我们在 IP 层上一般需要过滤的内容</p><figure class="highlight plaintext"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">ip // 协议过滤, 非ip协议的报文过滤掉</span><br><span class="line">ip.src == 192.168.10.121 // 源地址过滤</span><br><span class="line">ip.dst == 192.168.10.225 // 目标地址过滤</span><br><span class="line">ip.addr == 192.168.10.66 // 源或者目的地址过滤</span><br><span class="line">ip.dst [not] in {192.168.10.121, 192.168.10.225} // (不)在某几个值中</span><br><span class="line">ip.version == 4 // ip协议过滤</span><br><span class="line">ip.len > 100 // 如果需要, ip协议的其它信息也可以用于过滤</span><br></pre></td></tr></tbody></table></figure></li><li><p>传输层过滤 (TCP/UDP 协议信息过滤)</p><figure class="highlight plaintext"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">tcp // 协议过滤, 非tcp协议报文过滤掉</span><br><span class="line">tcp or udp // 协议过滤, 仅保留tcp或者udp报文</span><br><span class="line">tcp.srcport == 8788 // tcp源端口过滤</span><br><span class="line">udp.dstport != 8888 // udp目的端口过滤</span><br><span class="line">udp.dstport not in {8888, 8889}</span><br><span class="line">udp.dstport >= 2000 and udp.dstport <= 9000</span><br><span class="line">udp.port == 12345 // 源或者目的端口过滤</span><br></pre></td></tr></tbody></table></figure></li><li><p>应用层 / 用户数据过滤 (可以根据数据帧的特性，快速过滤出特定协议的数据包)</p><p>数据内容过滤时，中括号<strong>第一个数字是字节起始位置，第二个数字是字节长度</strong></p><figure class="highlight plaintext"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line">data.data[4:2] == 0300 // tcp/udp负载数据部分第字节开始的两字节为0300的包</span><br><span class="line">tcp.segment_data[0:2] == 4d15</span><br><span class="line">tcp.payload[0:2] == 6f72 // tcp负载数据过滤</span><br><span class="line">udp.payload[0:4] == 6f726179 // udp负载数据过滤</span><br><span class="line">data.len > 0 // 负载数据长度过滤</span><br><span class="line">data.data[0:1] == 6f // tcp/udp负载数据过滤</span><br><span class="line">data.data == 6f:72:61:79 // 整端数据匹配, 十六进制数据可以按照字节用:分开</span><br><span class="line">http.request.method == GET</span><br><span class="line">dns.qry.name == "www.baidu.com"</span><br><span class="line"></span><br><span class="line">http.request.uri contains "User" // contains 区分大小写</span><br><span class="line">http.host contains "baidu"</span><br><span class="line">http.request.uri matches "user" // matches 不区分大小写</span><br></pre></td></tr></tbody></table></figure></li></ul><p></p><h3 id="条件组合">条件组合</h3><p>以上的过滤条件都可以自由组合，使用 <code>and</code> <code>or</code><code>not</code>来连接多个判断条件</p><figure class="highlight plaintext"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">tcp.dstport in {12345, 12315} and http and ip.version == 6</span><br><span class="line">ip.addr == 192.168.31.2 and (udp.port == 12345 or tcp.port == 12345)</span><br></pre></td></tr></tbody></table></figure><p></p><h3 id="捕获数据导出">捕获数据导出</h3><ul><li>直接保存 (Save), 将保存指定时间内所有捕获的数据包，数据量一般非常大</li><li>导出特定分组 (Export Specified Packets), 可以选择只保存选中的包，或者已过滤的包 (Displayed), Range 参数可以选择保存第 xxx 包 - 第 yyy 包</li><li>导出分组解析结果 (Export Packet Dissections), 选择纯文本 (As PlainText), 可以过滤导出哪些包，同时可以在 Packet Format 中仅勾选 Packet Bytes,导出指定包的 hexdump</li></ul><p></p><p>一般来说为了便于分析，先初步过滤一下，比如 ip 过滤，然后将原始数据保存 (导出特定分组), 存储为<code>.pcapng</code></p><p>之后再使用 scapy 来进一步分析，重播，使用 scapy 重播可以取出特定层的原始数据，按照新的源 IP / 目标 IP 发送，或者发送到特定的 Socket</p><p></p><p></p><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kity.min.js"></script><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kityminder.core.min.js"></script><script defer="true" type="text/javascript" src="https://unpkg.com/[email protected]/dist/mindmap.min.js"></script><link rel="stylesheet" type="text/css" href="https://unpkg.com/[email protected]/dist/mindmap.min.css">]]></content>
<summary type="html"><h2 id="理解网络层次">理解网络层次</h2>
<p>OSI 五层协议</p>
<ul>
<li><p>物理层：一般是基于电信号进行 bit 流传输</p></li>
<li><p><strong>数据链路层</strong>: 定义 bit 信号分组方式，常见的协议是
以太网协议 (Ethernet)</p>
<p>Ethernet 数据帧 [帧头，数据，帧尾]</p></li>
<li><p><strong> 网络层</strong>: 划分广播域 / 子网，
一般网络层都是 IP 协议</p>
<p>IP 数据帧 [报头，数据]</p></li>
<li><p><strong> 传输层</strong>: 建立端口到端口的通信，
常见传输层协议有 TCP/UDP</p>
<p>TCP 基于连接，提供可靠传输，面向字节流，三次握手 / 四次挥手
(创建 / 断开连接), 粘包 / 拆包，timewait, 报文头长，总体传输慢，窗口，
拥塞控制</p>
<p>UDP 无连接，尽可能快，不可靠传输，面向报文，过长报文会被分片</p></li>
<li><p><strong>应用层</strong></p></li>
</ul>
<img data-src="/posts/8eb85eb3/network_layers.png" class="">
<p></p>
<p>使用 Wireshark 分析数据包时，一般关注的是后面三层，
每层的报文头中都包含了特定信息，在数据层存放更上层的数据</p></summary>
<category term="计算机基础" scheme="https://fetasty.github.io/categories/computer-science/"/>
<category term="计算机基础" scheme="https://fetasty.github.io/tags/computer-science/"/>
</entry>
<entry>
<title>函数调用约定</title>
<link href="https://fetasty.github.io/posts/377a3f70/"/>
<id>https://fetasty.github.io/posts/377a3f70/</id>
<published>2024-02-18T06:50:51.000Z</published>
<updated>2024-02-18T06:51:53.003Z</updated>
<content type="html"><![CDATA[<h2 id="函数调用约定分类">函数调用约定分类</h2><p>函数调用约定（CallingConvention）是规定函数在栈上的参数传递和清理方式的约定。不同的编程语言和编译器可能使用不同的调用约定，主要有以下几种常见的函数调用约定：</p><span id="more"></span><ol type="1"><li><p><strong>StdCall（标准调用约定）</strong> ：</p><ul><li>参数由调用者在栈上<strong>顺序压入</strong>，由<strong>被调用函数负责清理栈</strong>。</li><li><strong>函数名称在链接时由名称修饰器（namedecoration）进行修饰，用于指定函数的参数数量和类型</strong>。可以支持函数重载</li><li> Windows API 中的大部分函数使用标准调用约定。</li></ul></li><li><p><strong>Cdecl（C 调用约定）</strong> ：</p><ul><li>参数由调用者在栈上<strong>顺序压入</strong>，由<strong>调用者负责清理栈</strong>。</li><li><strong>函数名称在链接时不进行修饰</strong>。不支持函数重载</li><li>在 C 和 C++ 中常用的默认调用约定。</li></ul></li><li><p><strong>FastCall（快速调用约定）</strong> ：</p><ul><li>将一些参数（通常是寄存器数量限制内的参数）存放在寄存器中传递，剩余的参数由调用者在栈上压入。</li><li>寄存器用于存储参数的寄存器数量和顺序由编译器约定。</li><li>函数名称在链接时不进行修饰。</li><li>可以提高函数调用的性能。</li></ul></li><li><p><strong>ThisCall（成员函数调用约定）</strong> ：</p><ul><li>参数由调用者在栈上顺序压入，但第一个参数（this 指针）通过寄存器传递。</li><li>其余参数由调用者负责清理栈。</li><li>常用于非静态成员函数，this 指针通过 ECX 寄存器传递。</li></ul></li><li><p><strong>Winapi（Windows API 调用约定）</strong> ：</p><ul><li>与 StdCall 相同，参数由调用者在栈上顺序压入，由被调用函数负责清理栈。</li><li>函数名称在链接时不进行修饰。</li><li>在 Windows API 中，Winapi 通常是 StdCall 的同义词。</li></ul></li><li><p><strong>Pascal（帕斯卡调用约定）</strong> ：</p><ul><li>参数由调用者在栈上逆序压入，由被调用函数负责清理栈。</li><li>函数名称在链接时不进行修饰。</li><li>常用于 Delphi 等编程语言。</li></ul></li></ol><p>选择适当的函数调用约定主要取决于编程语言、平台和编译器的要求。通常情况下，你无需显式指定函数的调用约定，编译器会根据语言和平台的规范自动选择合适的调用约定。但在某些情况下，例如与非托管代码交互或使用特定的编译器选项时，可能需要手动指定函数的调用约定。</p><p>顺序压入（Arguments Pushed in Order）和逆序压入（Arguments Pushed inReverse Order）是函数调用过程中参数在栈上的压入顺序。</p><ol type="1"><li><strong>顺序压入</strong>：在顺序压入的调用约定中，函数参数按照从左到右的顺序依次压入栈中。也就是说，第一个参数被压入栈的位置最低，最后一个参数被压入栈的位置最高。这意味着栈的顶部是最后一个参数的位置。例如，假设有一个函数<code>void MyFunction(int a, int b, int c)</code>，使用顺序压入的调用约定时，参数<code>a</code> 会被首先压入栈，然后是参数 <code>b</code>，最后是参数<code>c</code>。在函数内部，通过访问栈上的相对偏移量，可以获取到相应的参数值。</li><li><strong>逆序压入</strong>：在逆序压入的调用约定中，函数参数按照从右到左的顺序依次压入栈中。也就是说，第一个参数被压入栈的位置最高，最后一个参数被压入栈的位置最低。这意味着栈的顶部是第一个参数的位置。例如，假设有一个函数<code>void MyFunction(int a, int b, int c)</code>，使用逆序压入的调用约定时，参数<code>c</code> 会被首先压入栈，然后是参数 <code>b</code>，最后是参数<code>a</code>。在函数内部，通过访问栈上的相对偏移量，可以获取到相应的参数值。</li></ol><p>顺序压入和逆序压入是两种不同的参数传递方式，而具体使用哪种方式取决于函数调用约定的规定。不同的编程语言、平台和编译器可能使用不同的参数压入顺序。因此，在编写和调用函数时，需要了解所使用的编程语言和调用约定的规范，以正确地传递参数。</p><h2 id="在c中指定函数的调用约定">在 C++ 中指定函数的调用约定</h2><figure class="highlight cpp"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="function">__cdecl <span class="type">void</span> <span class="title">MyFunction</span><span class="params">(<span class="type">int</span> a, <span class="type">int</span> b)</span></span>;</span><br><span class="line"><span class="function">__stdcall <span class="type">void</span> <span class="title">MyFunction</span><span class="params">(<span class="type">int</span> a, <span class="type">int</span> b)</span></span>;</span><br><span class="line"><span class="function">__fastcall <span class="type">void</span> <span class="title">MyFunction</span><span class="params">(<span class="type">int</span> a, <span class="type">int</span> b)</span></span>;</span><br><span class="line"><span class="keyword">class</span> <span class="title class_">MyClass</span></span><br><span class="line">{</span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line"> <span class="function">__thiscall <span class="type">void</span> <span class="title">MyMethod</span><span class="params">(<span class="type">int</span> a, <span class="type">int</span> b)</span></span>;</span><br><span class="line">};</span><br></pre></td></tr></tbody></table></figure><p>在 C++源码中，可以使用一些特定的关键字和修饰符来表示一个函数是导出函数。具体的表示方式取决于所使用的编译器和平台。</p><figure class="highlight cpp"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">ifdef</span> _WIN32</span></span><br><span class="line"> <span class="meta">#<span class="keyword">define</span> DLL_EXPORT __declspec(dllexport) <span class="comment">// Microsoft Visual C++ 编译器的扩展，用于指定一个函数是导出函数</span></span></span><br><span class="line"><span class="meta">#<span class="keyword">define</span> DLL_IMPORT __declspec(dllimport)</span></span><br><span class="line"><span class="meta">#<span class="keyword">else</span></span></span><br><span class="line"> <span class="meta">#<span class="keyword">define</span> DLL_EXPORT</span></span><br><span class="line"><span class="meta">#<span class="keyword">define</span> DLL_IMPORT</span></span><br><span class="line"><span class="meta">#<span class="keyword">endif</span></span></span><br><span class="line"></span><br><span class="line"><span class="function">DLL_EXPORT <span class="type">void</span> <span class="title">MyExportedFunction</span><span class="params">()</span></span>;</span><br></pre></td></tr></tbody></table></figure><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kity.min.js"></script><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kityminder.core.min.js"></script><script defer="true" type="text/javascript" src="https://unpkg.com/[email protected]/dist/mindmap.min.js"></script><link rel="stylesheet" type="text/css" href="https://unpkg.com/[email protected]/dist/mindmap.min.css">]]></content>
<summary type="html"><h2 id="函数调用约定分类">函数调用约定分类</h2>
<p>函数调用约定（Calling
Convention）是规定函数在栈上的参数传递和清理方式的约定。不同的编程语言和编译器可能使用不同的调用约定，主要有以下几种常见的函数调用约定：</p></summary>
<category term="C++" scheme="https://fetasty.github.io/categories/C/"/>
<category term="C++" scheme="https://fetasty.github.io/tags/C/"/>
</entry>
<entry>
<title>extern C 用法</title>
<link href="https://fetasty.github.io/posts/73245494/"/>
<id>https://fetasty.github.io/posts/73245494/</id>
<published>2024-02-18T06:27:34.000Z</published>
<updated>2024-02-18T06:46:56.545Z</updated>
<content type="html"><![CDATA[<h2 id="extern-c-作用">extern C 作用</h2><figure class="highlight cpp"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">ifdef</span> __cplusplus</span></span><br><span class="line"><span class="keyword">extern</span> <span class="string">"C"</span> {</span><br><span class="line"><span class="meta">#<span class="keyword">endif</span></span></span><br><span class="line"> <span class="comment">// 函数声明</span></span><br><span class="line"> <span class="comment">// 或者函数定义</span></span><br><span class="line"> <span class="comment">// 或者#include <C语言Header.h></span></span><br><span class="line"><span class="meta">#<span class="keyword">ifdef</span> __cplusplus</span></span><br><span class="line">}</span><br><span class="line"><span class="meta">#<span class="keyword">endif</span></span></span><br></pre></td></tr></tbody></table></figure><p><code>extern "C"</code><strong>修饰的变量和函数按照 C 语言方式编译和连接</strong></p><span id="more"></span><p>Cpp 和 C 编译的编译方式是不同的，比如对于相同的函数原型:<code>void foo(int x, int y)</code></p><p>C 语言中该函数被编译后在符号库中的名字是<code>_foo</code></p><p>Cpp 中，函数被编译器编译后，在符号库中的名字会带上参数类型，会产生像<code>_foo_int_int</code>(不同编译器可能生成的名字不同，但都使用相同机制) 之类的名字</p><p>Cpp <strong>也是依靠这种机制实现函数重载的</strong></p><p><code>extern "C"</code> 的作用就是指示编译器，将其修饰或包含的代码按照 C 语言方式编译，编译后的函数符号不包含参数类型，<strong>也正是因为这个，</strong><code>extern "C"</code><strong>中包含的代码不能包含重载函数</strong></p><h2 id="c与cpp中的使用">C 与 Cpp 中的使用</h2><h3 id="c语言中调用cpp代码">C 语言中调用 Cpp 代码</h3><p>当 Cpp 导出 C 语言格式的函数后，不仅 C 语言可以调用 Cpp 的函数；Cpp 编写的函数库 (lib/dll/a/so), 也可以以 C 语言函数接口为标准，提供给其它语言使用，比如 Python, C# 或者 Lua 等，以此实现多语言之间的混合使用 Cpp 头文件</p><figure class="highlight cpp"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// cpph.h</span></span><br><span class="line"><span class="meta">#<span class="keyword">ifndef</span> CPPH_H</span></span><br><span class="line"><span class="meta">#<span class="keyword">define</span> CPPH_H</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 只在C++中让extern "C"出现, C语言不支持该语法</span></span><br><span class="line"><span class="comment">// 用__cplusplus宏判断后, C++和C中可以共用这份头文件</span></span><br><span class="line"><span class="comment">// 即使编译为运行库, 也需要一份可以共用的接口头文件</span></span><br><span class="line"><span class="meta">#<span class="keyword">ifdef</span> __cplusplus</span></span><br><span class="line"><span class="keyword">extern</span> <span class="string">"C"</span> {</span><br><span class="line"><span class="meta">#<span class="keyword">endif</span></span></span><br><span class="line"><span class="function"><span class="type">int</span> <span class="title">add</span><span class="params">(<span class="type">int</span> x, <span class="type">int</span> y)</span></span>;</span><br><span class="line"><span class="meta">#<span class="keyword">ifdef</span> __cplusplus</span></span><br><span class="line">}</span><br><span class="line"><span class="meta">#<span class="keyword">endif</span></span></span><br><span class="line"></span><br><span class="line"><span class="meta">#<span class="keyword">endif</span></span></span><br></pre></td></tr></tbody></table></figure><p>Cpp 实现源码 (或者实现的函数库 lib/dll)</p><figure class="highlight cpp"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// cpph.cc</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">"cpph.h"</span></span></span><br><span class="line"><span class="function"><span class="type">int</span> <span class="title">add</span><span class="params">(<span class="type">int</span> x, <span class="type">int</span> y)</span> </span>{</span><br><span class="line"> <span class="keyword">return</span> x + y;</span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure><p>C 语言文件</p><figure class="highlight cpp"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// c_file.c</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string"><stdio.h></span></span></span><br><span class="line"><span class="function"><span class="keyword">extern</span> <span class="type">int</span> <span class="title">add</span><span class="params">(<span class="type">int</span> x, <span class="type">int</span> y)</span></span>; <span class="comment">// 或者#include "cpph.h", 包含Cpp头文件</span></span><br><span class="line"><span class="function"><span class="type">void</span> <span class="title">main</span><span class="params">()</span> </span>{</span><br><span class="line"> <span class="type">int</span> result = <span class="built_in">add</span>(<span class="number">3</span>, <span class="number">5</span>);</span><br><span class="line"> <span class="built_in">printf</span>(<span class="string">"%d\n"</span>, result);</span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure><h3 id="cpp中调用c代码">Cpp 中调用 C 代码</h3><p>C 头文件</p><figure class="highlight cpp"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// chead.h</span></span><br><span class="line"><span class="meta">#<span class="keyword">ifndef</span> CHEAD_H</span></span><br><span class="line"><span class="meta">#<span class="keyword">define</span> CHEAD_H</span></span><br><span class="line"><span class="function"><span class="keyword">extern</span> <span class="type">int</span> <span class="title">add</span><span class="params">(<span class="type">int</span> x, <span class="type">int</span> y)</span></span>;</span><br><span class="line"><span class="meta">#<span class="keyword">endif</span></span></span><br></pre></td></tr></tbody></table></figure><p>C 源文件</p><figure class="highlight cpp"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// chead.c</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">"chead.h"</span></span></span><br><span class="line"><span class="function"><span class="type">int</span> <span class="title">add</span><span class="params">(<span class="type">int</span> x, <span class="type">int</span> y)</span> </span>{</span><br><span class="line"> <span class="keyword">return</span> x + y;</span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure><p>Cpp 中调用</p><figure class="highlight cpp"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string"><iostream></span></span></span><br><span class="line"><span class="comment">// 或者 extern "C" int add(int x, int y);</span></span><br><span class="line"><span class="keyword">extern</span> <span class="string">"C"</span> {</span><br><span class="line"> <span class="meta">#<span class="keyword">include</span> <span class="string">"chead.h"</span></span></span><br><span class="line">}</span><br><span class="line"><span class="function"><span class="type">int</span> <span class="title">main</span><span class="params">()</span> </span>{</span><br><span class="line"> <span class="type">int</span> c = <span class="built_in">add</span>(<span class="number">100</span>, <span class="number">200</span>);</span><br><span class="line"> std::cout << c << std::endl;</span><br><span class="line"> <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kity.min.js"></script><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kityminder.core.min.js"></script><script defer="true" type="text/javascript" src="https://unpkg.com/[email protected]/dist/mindmap.min.js"></script><link rel="stylesheet" type="text/css" href="https://unpkg.com/[email protected]/dist/mindmap.min.css">]]></content>
<summary type="html"><h2 id="extern-c-作用">extern C 作用</h2>
<figure class="highlight cpp"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">ifdef</span> __cplusplus</span></span><br><span class="line"><span class="keyword">extern</span> <span class="string">"C"</span> {</span><br><span class="line"><span class="meta">#<span class="keyword">endif</span></span></span><br><span class="line"> <span class="comment">// 函数声明</span></span><br><span class="line"> <span class="comment">// 或者函数定义</span></span><br><span class="line"> <span class="comment">// 或者#include &lt;C语言Header.h&gt;</span></span><br><span class="line"><span class="meta">#<span class="keyword">ifdef</span> __cplusplus</span></span><br><span class="line">}</span><br><span class="line"><span class="meta">#<span class="keyword">endif</span></span></span><br></pre></td></tr></tbody></table></figure>
<p><code>extern "C"</code><strong>修饰的变量和函数按照 C 语言方式编译和连接</strong></p></summary>
<category term="C++" scheme="https://fetasty.github.io/categories/C/"/>
<category term="C++" scheme="https://fetasty.github.io/tags/C/"/>
</entry>
<entry>
<title>位运算</title>
<link href="https://fetasty.github.io/posts/2633a26/"/>
<id>https://fetasty.github.io/posts/2633a26/</id>
<published>2024-01-17T02:06:12.000Z</published>
<updated>2024-01-17T10:23:28.661Z</updated>
<content type="html"><![CDATA[<p>位运算是计算机中最常用的操作之一，运用好位运算可以在特定情况下大幅提高计算效率</p><h2 id="原反补码">原反补码</h2><p>正数的原反补码都是自身 负数的补码为原码取反，符号位不变；补码为反码加 1, 符号位需要进位时丢弃进位符号位变 0 (进位溢出)计算机中的数字都是以补码表示</p><h2 id="有符号整型的二进制位">有符号整型的二进制位</h2><p>以 char (signed char, 1 字节) 为例</p><figure class="highlight plaintext"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">0 = 0000 0000 b</span><br><span class="line">-1 = 1111 1111 b</span><br></pre></td></tr></tbody></table></figure><span id="more"></span><h2 id="移位操作">移位操作</h2><h3 id="左移">左移</h3><p>以 cpp 为例，左移操作是将数据的所有二进制位都向左移动一定位数，高位丢弃，低位补 0</p><p>左移 1 位相当于原数据乘以<span class="math inline"> \(2^1\)</span>,左移 n 位相当于原数据乘以<span class="math inline"> \(2^n\)</span>,高位丢弃相当于乘以<span class="math inline"> \(2^n\)</span> 后高位溢出</p><p></p><h3 id="右移">右移</h3><p>右移操作需要分情况</p><ol type="1"><li>有符号正数，符号位为 0, 右移低位丢弃，高位补 0</li><li> 有符号负数，符号位为 1, 右移低位丢弃，高位补 1</li><li> 无符号整数，右移低位丢弃，高位补 0</li></ol><p>右移 1 位相当于数字除以<span class="math inline"> \(2^1\)</span>,右移 n 位相当于除以<span class="math inline"> \(2^n\)</span>,低位丢弃的数字相当于整数除法的精度丢失</p><p></p><p>移位的操作效果相当于乘除<span class="math inline"> \(2^n\)</span>,但是移位的操作效率比乘除运算的效率更高</p><p>如果整数无法被<span class="math inline"> \(2^n\)</span> 整除，尾部的小数部分被丢弃，相当于结果减去了小数部分，所以右移可能结果会偏小(向下取整), 因此 -1 右移之后还是 -1, 二进制位不变</p><figure class="highlight cpp"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">(<span class="number">-5</span>) >> <span class="number">1</span>; <span class="comment">// -3, 11111111 11111111 11111111 11111101</span></span><br><span class="line"><span class="number">5</span> >> <span class="number">1</span>; <span class="comment">// 2, 00000000 00000000 00000000 00000010</span></span><br><span class="line"><span class="number">-1</span>; <span class="comment">// 11111111 11111111 11111111 11111111</span></span><br><span class="line"><span class="number">-1</span> >> <span class="number">1</span>; <span class="comment">// -1, 11111111 11111111 11111111 11111111</span></span><br><span class="line"><span class="type">uint32_t</span> num = (<span class="type">uint32_t</span>)<span class="number">-1</span>; <span class="comment">// 4294967295, 11111111 11111111 11111111 11111111</span></span><br><span class="line">num >> <span class="number">1</span>; <span class="comment">// 2147483647, 01111111 11111111 11111111 11111111</span></span><br></pre></td></tr></tbody></table></figure><p></p><h2 id="读写数据的二进制位">读写数据的二进制位</h2><p>可以通过 "与" 和 "或" 操作来读写一个数据的对应位，虽然本文源码以 <code>C++</code>为例，但这在多数语言中都是相通的操作</p><p>使用 Python 时需要注意一下，Python 的整数是使用数组实现，其长度可以无限大，不像普通语言，整数类型具有固定或有限长度</p><figure class="highlight cpp"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="type">int</span> test = <span class="number">123</span>; <span class="comment">// C++中的int一般为32位整型</span></span><br><span class="line"><span class="comment">// 读取所有的二进制位</span></span><br><span class="line"><span class="keyword">for</span> (<span class="type">int</span> i = <span class="number">31</span>; i >= <span class="number">0</span>; --i) {</span><br><span class="line"> <span class="built_in">printf</span>(<span class="string">"%d"</span>, (test & (<span class="number">0x1</span> << i)) != <span class="number">0</span> ? <span class="number">1</span> : <span class="number">0</span>);</span><br><span class="line">}</span><br><span class="line"><span class="comment">// 输出: 00000000000000000000000001111011</span></span><br><span class="line"><span class="comment">// 将倒数第2位设置为0</span></span><br><span class="line">test &= ~(<span class="number">0x1</span> << <span class="number">1</span>); <span class="comment">// 00000000000000000000000001111001</span></span><br><span class="line"><span class="comment">// 再将倒数第3位设置为1</span></span><br><span class="line">test |= (<span class="number">0x1</span> << <span class="number">2</span>); <span class="comment">// 00000000000000000000000001111101</span></span><br></pre></td></tr></tbody></table></figure><p>这样的话，我们可以将一个整型变量当作一个 bit 数组使用，对任意位进行读写</p><p>但是 int 只有 32 位长度，如果我们需要更大的 bit 数组怎么办呢，int64 吗？要是需要的长度远大于 64 呢？</p><p>我们可以使用整型数组来当作一个大的 bit 数组使用，而且数组的内存是连续的，非常容易操作</p><figure class="highlight cpp"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 我们将一个长度为5的int数组当作160位的bit数组使用</span></span><br><span class="line"><span class="type">int</span> bit_arr[<span class="number">5</span>] = {<span class="number">0</span>};</span><br><span class="line"><span class="comment">// 将第100位(从左到右)设置为1</span></span><br><span class="line"><span class="type">int</span> int_index = <span class="number">100</span> / <span class="number">32</span>; <span class="comment">// 先取得bit对应的int下标</span></span><br><span class="line"><span class="type">int</span> bit_index = (<span class="number">100</span> % <span class="number">32</span>); <span class="comment">// 再取得bit在对应int中的下标</span></span><br><span class="line">bit_arr[int_index] |= (<span class="number">0x1</span> << (<span class="number">31</span> - bit_index)); <span class="comment">// int最左的1位需要左移31位才能访问</span></span><br><span class="line"><span class="comment">// 同理, 取得第100位的bit值也是一样的步骤, 先计算int下标, 再计算int内的bit下标</span></span><br><span class="line"><span class="type">int</span> bit_value = (bit_arr[int_index] & (<span class="number">0x1</span> << (<span class="number">31</span> - bit_index))) != <span class="number">0</span> ? <span class="number">1</span> : <span class="number">0</span>;</span><br></pre></td></tr></tbody></table></figure><p>可以再进一步，将上述计算封装起来，仅对外暴露简单易用的接口，很多语言的标准库中都封装好了，比如 cpp 中的 bitset,有兴趣可以自己封装试试</p><p></p><p></p><h2 id="数据转为二进制字符串">数据转为二进制字符串</h2><figure class="highlight cpp"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">template</span><<span class="keyword">typename</span> T></span></span><br><span class="line"><span class="function"><span class="type">void</span> <span class="title">print_bin</span><span class="params">(T data)</span> </span>{</span><br><span class="line"> std::string str;</span><br><span class="line"> <span class="type">uint8_t</span>* bytes = (<span class="type">uint8_t</span>*)&data;</span><br><span class="line"> <span class="keyword">auto</span> len = <span class="built_in">sizeof</span>(T);</span><br><span class="line"> <span class="keyword">for</span> (<span class="type">int</span> i = len - <span class="number">1</span>; i >= <span class="number">0</span>; --i) {</span><br><span class="line"> <span class="type">uint8_t</span> v = bytes[i];</span><br><span class="line"> <span class="keyword">for</span> (<span class="type">int</span> j = <span class="number">8</span> - <span class="number">1</span>; j >= <span class="number">0</span>; --j) {</span><br><span class="line"> str.<span class="built_in">append</span>((v & (<span class="number">0x1</span> << j)) > <span class="number">0</span> ? <span class="string">"1"</span> : <span class="string">"0"</span>);</span><br><span class="line"> }</span><br><span class="line"> str.<span class="built_in">append</span>(<span class="string">" "</span>);</span><br><span class="line"> }</span><br><span class="line"> <span class="built_in">printf</span>(<span class="string">"%s\n"</span>, str.<span class="built_in">c_str</span>());</span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure><h2 id="数据按位取反之后得到的值是什么">数据按位取反之后得到的值是什么</h2><p>先利用上述的 <code>print_bin</code>看看 <code>6</code> <code>-6</code><code>~6</code>的二进制</p><figure class="highlight cpp"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">print_bin</span>(<span class="number">6</span>)</span><br><span class="line"><span class="built_in">print_bin</span>(<span class="number">-6</span>)</span><br><span class="line"><span class="built_in">printf</span>(<span class="string">"%d\n"</span>, ~<span class="number">6</span>)</span><br><span class="line"><span class="built_in">print_bin</span>(~<span class="number">6</span>)</span><br></pre></td></tr></tbody></table></figure><p>结果如下</p><figure class="highlight plaintext"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">11111111 11111111 11111111 11111010 // -6 的二进制（补码）</span><br><span class="line">00000000 00000000 00000000 00000110 // 6 的二进制（补码）</span><br><span class="line">-7</span><br><span class="line">11111111 11111111 11111111 11111001 // ~6 的二进制, 可以看到, 其真值为-7</span><br></pre></td></tr></tbody></table></figure><p><code>~6</code>为什么是 <code>-7</code>呢，其实我们将 <code>-7</code>的补码写出来就会发现，它与 <code>~6</code>的二进制完全一样</p><p>好像发现了点什么，我们再看看 <code>~(-6)</code></p><figure class="highlight cpp"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">print_bin</span>(<span class="number">-6</span>)</span><br><span class="line"><span class="built_in">printf</span>(<span class="string">"%d\n"</span>, ~(<span class="number">-6</span>))</span><br><span class="line"><span class="built_in">print_bin</span>(~(<span class="number">-6</span>))</span><br></pre></td></tr></tbody></table></figure><p>结果如下</p><figure class="highlight plaintext"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">11111111 11111111 11111111 11111010 // -6的二进制 (-6的补码)</span><br><span class="line">5</span><br><span class="line">00000000 00000000 00000000 00000101 // ~(-6)的二进制 (5的补码)</span><br></pre></td></tr></tbody></table></figure><p><code>6</code>取反得到 <code>-7</code>,<code>-6</code>取反得到 <code>5</code>,难道对一个整数取反就是它的相反数减去 1?</p><p>我们多用几个数字测试一下，包含特殊值 0</p><figure class="highlight cpp"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">for</span> (<span class="type">int</span> i = <span class="number">-3</span>; i < <span class="number">4</span>; ++i)</span><br><span class="line">{</span><br><span class="line"><span class="built_in">printf</span>(<span class="string">"%d %d\n"</span>, i, ~i + <span class="number">1</span>);</span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure><p>结果如下，0 也符合预期</p><figure class="highlight plaintext"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">-3 3</span><br><span class="line">-2 2</span><br><span class="line">-1 1</span><br><span class="line">0 0</span><br><span class="line">1 -1</span><br><span class="line">2 -2</span><br><span class="line">3 -3</span><br></pre></td></tr></tbody></table></figure><p>到此我们其实得到了一个普适的规律: <code>~n + 1 = -n</code>也就是<strong>对一个整数取反 (~) 并加 1 得到它的相反数</strong></p><h2 id="取得二进制位最右边的1">取得二进制位最右边的 1</h2><figure class="highlight cpp"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="type">int</span> mostRightOne = n & (~n + <span class="number">1</span>);</span><br></pre></td></tr></tbody></table></figure><p>根据以上章节提到的结论 <code>~n + 1 = -n</code>可以得到以下等价代码</p><figure class="highlight cpp"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="type">int</span> mostRightOne = n & (-n);</span><br></pre></td></tr></tbody></table></figure><h2 id="使用异或交换两个数字">使用异或交换两个数字</h2><ul><li><p>任何数字异或自身等于 0 <code>a ^ a == 0</code></p></li><li><p>任何数字与 0 异或等于自身 <code>a ^ 0 == a</code></p></li><li><p>异或满足交换律和结合律<code>a ^ b == b ^ aa ^ (b ^ c) == (a ^ b) ^ c</code></p><figure class="highlight cpp"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="type">int</span> a = <span class="number">1</span>, b = <span class="number">2</span>;</span><br><span class="line">a = a ^ b;</span><br><span class="line">b = a ^ b;</span><br><span class="line">a = a ^ b:</span><br></pre></td></tr></tbody></table></figure></li></ul><p></p><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kity.min.js"></script><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kityminder.core.min.js"></script><script defer="true" type="text/javascript" src="https://unpkg.com/[email protected]/dist/mindmap.min.js"></script><link rel="stylesheet" type="text/css" href="https://unpkg.com/[email protected]/dist/mindmap.min.css">]]></content>
<summary type="html"><p>位运算是计算机中最常用的操作之一，
运用好位运算可以在特定情况下大幅提高计算效率</p>
<h2 id="原反补码">原反补码</h2>
<p>正数的原反补码都是自身 负数的补码为原码取反，符号位不变；
补码为反码加 1, 符号位需要进位时丢弃进位符号位变 0 (进位溢出)
计算机中的数字都是以补码表示</p>
<h2 id="有符号整型的二进制位">有符号整型的二进制位</h2>
<p>以 char (signed char, 1 字节) 为例</p>
<figure class="highlight plaintext"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">0 = 0000 0000 b</span><br><span class="line">-1 = 1111 1111 b</span><br></pre></td></tr></tbody></table></figure></summary>
<category term="数据结构&设计模式" scheme="https://fetasty.github.io/categories/algorithm-and-design-pattern/"/>
<category term="数据结构&设计模式" scheme="https://fetasty.github.io/tags/algorithm-and-design-pattern/"/>
</entry>
<entry>
<title>ArchLinux 使用</title>
<link href="https://fetasty.github.io/posts/2d9deefc/"/>
<id>https://fetasty.github.io/posts/2d9deefc/</id>
<published>2023-12-09T02:53:22.000Z</published>
<updated>2023-12-11T06:46:34.275Z</updated>
<content type="html"><![CDATA[<p>Arch 是众多 Linux 发行版中的其中一个，但是它比较纯净，同时安装也相比于其它的 Linux 发行版复杂一些，从头安装一个 ArchLinux 可以学习不少 Linux 知识</p><p>推荐按照官方的安装教程一步步执行:https://wiki.archlinux.org/title/Installation_guide</p><p>最好阅读英文版，更新日期比较新</p><p>以下是折腾 Arch 的记录</p><span id="more"></span><h2 id="安装步骤">1 安装步骤</h2><h3 id="制作启动u盘">1.1 制作启动 U 盘</h3><ul><li>镜像文件下载: https://archlinux.org/download/</li><li> 使用 rufus 等工具制作 UEFI 启动盘</li><li> BIOS 中设置启动模式为 UEFI</li><li> 通过 U 盘启动</li></ul><h3 id="连接网络">1.2 连接网络</h3><p>U 盘启动后是一个用于安装系统的 Linux 环境，必须连接到网络才能进行 archlinux 的安装</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># 查看网卡状态, 打开网口</span></span><br><span class="line">ip <span class="built_in">link</span></span><br><span class="line">ip <span class="built_in">link</span> <span class="built_in">set</span> dev [interface] up</span><br><span class="line"></span><br><span class="line"><span class="comment"># iwctl 连接wifi</span></span><br><span class="line">iwctl <span class="comment"># 进入iwc交互模式</span></span><br><span class="line">[iwd] <span class="built_in">help</span></span><br><span class="line">[iwd] device list</span><br><span class="line">[iwd] device [device] set-property Powered on</span><br><span class="line">[iwd] adapter [adapter] set-property Powered on</span><br><span class="line">[iwd] station [device] scan</span><br><span class="line">[iwd] station [device] get-networks</span><br><span class="line">[iwd] station [device] connect SSID</span><br><span class="line"></span><br><span class="line"><span class="comment"># 检测网络</span></span><br><span class="line">ping archlinux.org</span><br></pre></td></tr></tbody></table></figure><p>如果 wifi 不好连接，可直接使用网线连接</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># 查看系统ip地址</span></span><br><span class="line">ip addr</span><br></pre></td></tr></tbody></table></figure><p>之后使用 ssh 远程连接，方便操作</p><h3 id="同步系统时钟">1.3 同步系统时钟</h3><p>同步系统时钟</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># 开启时间同步</span></span><br><span class="line">timedatectl set-ntp <span class="literal">true</span></span><br><span class="line"><span class="comment"># 时区不对先不用管</span></span><br><span class="line">timedatectl</span><br></pre></td></tr></tbody></table></figure><h3 id="磁盘分区">1.4 磁盘分区</h3><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># 查看磁盘设备</span></span><br><span class="line">lsblk</span><br><span class="line">fdisk -l</span><br><span class="line"></span><br><span class="line"><span class="comment"># 使用fdisk分区</span></span><br><span class="line">fdisk /dev/[nvme0n1] <span class="comment"># 需要分区的磁盘设备, 交互式操作, m查看帮助, 创建GTP分区表, 分区开始位置自动, 结束位置可以使用+1G的方式确定</span></span><br></pre></td></tr></tbody></table></figure><p>一般来说，一个 linux 系统需要以下 3 个分区</p><table><colgroup><col style="width: 12%"><col style="width: 30%"><col style="width: 57%"></colgroup><thead><tr class="header"><th>挂载点</th><th>大小</th><th>说明</th></tr></thead><tbody><tr class="odd"><td><code>/boot</code></td><td>300M ~ 1G</td><td>EFI 分区，一般需要是磁盘第一个分区</td></tr><tr class="even"><td><code>[swap]</code></td><td>4G ~ 32G (看心情)</td><td> 交换分区，内存不足时用于缓存</td></tr><tr class="odd"><td><code>/</code></td><td>剩余所有</td><td> linux 系统根目录</td></tr></tbody></table><p>也可以根据需要将 <code>/home</code>, <code>/root</code>,<code>/srv</code> 或者 <code>/var</code> 等进行单独分区，以便于数据备份</p><p>fdisk 分区写入后，退出交互操作，格式化各分区</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># 格式化分区</span></span><br><span class="line">mkfs.ext4 /dev/[root_partition] <span class="comment"># 以及其它linux文件分区, /home, /root, /srv</span></span><br><span class="line">mkswap /dev/[swap_partition]</span><br><span class="line">mkfs.fat -F 32 /dev/[efi_system_partition] <span class="comment"># EFI分区必须格式化为FAT32格式</span></span><br></pre></td></tr></tbody></table></figure><h3 id="挂载系统分区">1.5 挂载系统分区</h3><p>所有的分区都要按照实际情况挂载上去，包括交换分区，之后的 <code>genfstab</code> 命令会检测所有的挂载分区和交换分区</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># 首先挂载根分区</span></span><br><span class="line">mount /dev/[root_partition] /mnt</span><br><span class="line">mount --<span class="built_in">mkdir</span> /dev/[efi_system_partition] /mnt/boot</span><br><span class="line"><span class="comment"># 如果有自定义的其余分区, 也都挂载进来</span></span><br><span class="line">mount --<span class="built_in">mkdir</span> /dev/[home_partition] /mnt/home</span><br><span class="line">mount --<span class="built_in">mkdir</span> /dev/[root_home_partition] /mnt/root</span><br><span class="line">mount --<span class="built_in">mkdir</span> /dev/[srv_partition] /mnt/srv</span><br><span class="line"><span class="comment"># 如果有swap分区, 也打开它</span></span><br><span class="line">swapon /dev/[swap_partition]</span><br></pre></td></tr></tbody></table></figure><h3 id="更改pacman镜像源">1.6 更改 pacman 镜像源</h3><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">nano /etc/pacman.d/mirrorlist</span><br><span class="line"><span class="comment"># 源的优先级取决于顺序, 可以将以下国内源添加在最上方</span></span><br><span class="line"><span class="comment"># Server = https://mirrors.tuna.tsinghua.edu.cn/archlinux/$repo/os/$arch</span></span><br></pre></td></tr></tbody></table></figure><h3 id="安装系统">1.7 安装系统</h3><p>首先安装必须的基本包</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">pacstrap -K /mnt base linux linux-firmware</span><br></pre></td></tr></tbody></table></figure><p>配置系统</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># 将分区挂载信息写入fstab文件, 生成文件后检查文件是否有错</span></span><br><span class="line">genfstab -U /mnt >> /mnt/etc/fstab</span><br></pre></td></tr></tbody></table></figure><p>change root 到新系统下</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">arch-chroot /mnt</span><br></pre></td></tr></tbody></table></figure><p>设置系统时间时区</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">ln</span> -sf /usr/share/zoneinfo/[Asia/Shanghai] /etc/localtime</span><br><span class="line">hwclock --systohc <span class="comment"># 写入系统时间bios</span></span><br></pre></td></tr></tbody></table></figure><p>本地化配置</p><p>编辑 <code>/etc/locale.gen</code>, 取消注释<code>en_US.UTF-8 UTF-8</code>, 执行以下命名</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">locale-gen</span><br></pre></td></tr></tbody></table></figure><p>创建 <code>/etc/locale.conf</code>, 填入以下内容</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">LANG=en_US.UTF-8</span><br></pre></td></tr></tbody></table></figure><p>设置网络名称</p><p>创建 <code>/etc/hostname</code> 文件，并填写自己的 <code>hostname</code></p><p>更改 root 账户密码</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">passwd</span><br></pre></td></tr></tbody></table></figure><p>安装配置 grub</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># 更新源信息</span></span><br><span class="line">pacman -Sy</span><br><span class="line">pacman -S grub</span><br><span class="line"><span class="comment"># 安装启动文件</span></span><br><span class="line">grub-install --target=x86_64-efi --efi-directory=[/boot] --bootloader-id=GRUB</span><br><span class="line"><span class="comment"># 生成grub配置</span></span><br><span class="line">grub-mkconfig -o /boot/grub/grub.cfg</span><br></pre></td></tr></tbody></table></figure><p>安装 microcode 微码包</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># intel cpu安装intel-ucode, amd cpu安装amd-ucode</span></span><br><span class="line">pacman -S amd-ucode</span><br></pre></td></tr></tbody></table></figure><p>微码包应该尽量早的加载，可以通过 grub 配置</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># 重新运行grub配置, 将自动检测微码包资源, 并放在最开始加载</span></span><br><span class="line">grub-mkconfig -o /boot/grub/grub.cfg</span><br><span class="line"><span class="comment"># 在/boot/grub/grub.cfg中应该能看到以下配置</span></span><br><span class="line"><span class="comment"># initrd /boot/[cpu_manufacturer]-ucode.img /boot/initramfs-linux.img</span></span><br></pre></td></tr></tbody></table></figure><p>安装基本软件</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># 安装需要的软件</span></span><br><span class="line">pacman -S base-devel openssh nano dhcpcd wpa_supplicant neofetch dmidecode radeontop</span><br></pre></td></tr></tbody></table></figure><p>配置网络和 ssh (以免重启后未联网，还要重新操作，或者连接显示器，比较麻烦)</p><p>参考</p><p>https://wiki.archlinux.org/title/Network_configuration/Wireless</p><p>https://wiki.archlinux.org/title/Dhcpcd</p><p>https://wiki.archlinux.org/title/Wpa_supplicant</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># 编辑ssh配置, 允许root登录</span></span><br><span class="line">nano /etc/ssh/sshd_config <span class="comment"># PermitRootLogin yes</span></span><br><span class="line"></span><br><span class="line"><span class="comment"># 打开ssh自启动</span></span><br><span class="line">systemctl <span class="built_in">enable</span> sshd</span><br><span class="line"></span><br><span class="line"><span class="comment"># 添加dhcp对wpa_supplicant(wifi wpa)的hook</span></span><br><span class="line"><span class="built_in">ln</span> -s /usr/share/dhcpcd/hooks/10-wpa_supplicant /usr/lib/dhcpcd/dhcpcd-hooks/</span><br><span class="line"></span><br><span class="line"><span class="comment"># 查看网口</span></span><br><span class="line">ip <span class="built_in">link</span></span><br><span class="line"></span><br><span class="line"><span class="comment"># 仅开启无线网口的自启动配置, 如果没有@xxx, 那么会自启动所有网口</span></span><br><span class="line">systemctl <span class="built_in">enable</span> dhcpcd@[wlan0].service</span><br><span class="line"></span><br><span class="line"><span class="comment"># wpa_supplicant配置, wpa_supplicant会由dhcpcd自动打开, 如果使用systemctl自启动, 也可以开启wpa_supplicant@[wlan0].service</span></span><br><span class="line">wpa_passphrase [MYSSID] [passphrase] > /etc/wpa_supplicant/wpa_supplicant-[wlan0].conf</span><br></pre></td></tr></tbody></table></figure><p>配置好所有内容后，重启系统</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># 关机使用poweroff</span></span><br><span class="line">reboot</span><br></pre></td></tr></tbody></table></figure><h2 id="使用pacman">2 使用 pacman</h2><p>帮助: <code>pacman -h</code></p><p>标签帮助: <code>pacman -Sh</code></p><p>更新软件源: <code>pacman -Sy</code></p><p>更新源并更新系统: <code>pacman -Syu</code></p><p>搜索在线包: <code>pacman -Ss <package_name></code></p><p>安装包: <code>pacman -S <package_name></code></p><p><code>pacman -Rns <package_name></code>删除软件以及不被其他软件依赖的包 (<code>-Rsu</code>可能删除其他软件包还在依赖的项，不安全)</p><p><code>pacman -Rc <package_name></code>删除软件包以及其配置项 (可以先使用</p><p><code>pacman -Qdtq</code> 列出不再被其它软件包依赖的软件包名称</p><h2 id="常用软件">3 常用软件</h2><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># 查看cpu核心信息</span></span><br><span class="line">lscpu -e</span><br><span class="line"><span class="comment"># 查看各传感器温度</span></span><br><span class="line">pacman -Syu</span><br><span class="line">pacman -S lm_sensors <span class="comment"># 工具集, 可以搜索以下lm_sensors其余用法</span></span><br><span class="line">sensors <span class="comment"># 查看硬件温度</span></span><br><span class="line"><span class="comment"># 查看内存占用</span></span><br><span class="line">free -h</span><br><span class="line"><span class="comment"># 查看磁盘占用</span></span><br><span class="line"><span class="built_in">df</span> -h</span><br><span class="line"><span class="comment"># 查看系统信息</span></span><br><span class="line">pacman -S neofetch</span><br><span class="line">neofetch</span><br><span class="line"><span class="comment"># 查看磁盘分区详情</span></span><br><span class="line">lsblk</span><br><span class="line">fdisk -l</span><br><span class="line"><span class="comment"># 查看pci设备</span></span><br><span class="line">lspci [-k]</span><br><span class="line"><span class="comment"># 查看硬件信息</span></span><br><span class="line">dmidecode [-t memory]</span><br><span class="line"><span class="comment"># 查看amd显卡信息</span></span><br><span class="line">radeontop</span><br></pre></td></tr></tbody></table></figure><p>至此已安装完毕</p><h2 id="展示环节">4 展示环节</h2><img data-src="/posts/2d9deefc/sensors.png" class=""><img data-src="/posts/2d9deefc/cpu_ram.png" class=""><img data-src="/posts/2d9deefc/radeontop.png" class=""><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kity.min.js"></script><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kityminder.core.min.js"></script><script defer="true" type="text/javascript" src="https://unpkg.com/[email protected]/dist/mindmap.min.js"></script><link rel="stylesheet" type="text/css" href="https://unpkg.com/[email protected]/dist/mindmap.min.css">]]></content>
<summary type="html"><p>Arch 是众多 Linux 发行版中的其中一个，但是它比较纯净，
同时安装也相比于其它的 Linux 发行版复杂一些，
从头安装一个 ArchLinux 可以学习不少 Linux 知识</p>
<p>推荐按照官方的安装教程一步步执行:
https://wiki.archlinux.org/title/Installation_guide</p>
<p>最好阅读英文版，更新日期比较新</p>
<p>以下是折腾 Arch 的记录</p></summary>
<category term="Linux" scheme="https://fetasty.github.io/categories/Linux/"/>
<category term="Linux" scheme="https://fetasty.github.io/tags/Linux/"/>
<category term="Arch" scheme="https://fetasty.github.io/tags/Arch/"/>
</entry>
<entry>
<title>Android 手机改造 Linux 服务器</title>
<link href="https://fetasty.github.io/posts/df321891/"/>
<id>https://fetasty.github.io/posts/df321891/</id>
<published>2023-12-08T13:50:30.000Z</published>
<updated>2023-12-11T06:46:34.258Z</updated>
<content type="html"><![CDATA[<p>手头上的旧手机为小米 6, 本文可能部分内容只在小米 6 上适用 [xiaomi 6sagit]</p><p>且本文主要讨论 LinuxDeploy (需要 root) 的方式，非 root 用户可使用 Termux 方式</p><span id="more"></span><h2 id="方案选择">1 方案选择</h2><p>前后测试了 3 种方法，最推荐使用 LinuxDeploy (chroot)</p><ul><li>Ubuntu touch 原生 Linux 系统，但是为了驱动手机设备，需要做很多工作，社区上适用于 xiaomi6 的 ubuntu touch 已经停止开发了，使用起来还有很多不足，<code>apt update && apt upgrade</code> 一下，可能设备就无法启动了</li><li> Termux (proot), Termux 本身的文件结构与 linux 系统不同，使用 proot 方式运行 linux, 性能有损耗 (但是并不多),对于非 root 用户该方式非常不错，而且可以通过 Termux-boot 插件实现自启动</li><li> LinuxDeploy (chroot), 需要 root 权限，初略了解，它应该比 proot 方式性能更好，原本的 Android 系统负责驱动设备硬件，维护设备运行，而 chroot 中的 linux 并行于 Android 系统运行，不必关心硬件设备的驱动</li></ul><p>使用 LinuxDeploy 的同时将系统刷为 lineageos, 使用原生安卓系统驱动设备，保证手机正常工作，同时尽量少的占用资源，不安装不开启不必要的应用，不过刷系统是个可选项，使用原生系统也问题不大</p><p>chroot (change root) 是一种非常原始的容器技术，仅仅是将一个进程的根目录更改到一个指定目录，限制访问和可见性，其余的硬件资源，网络资源等则还是和宿主系统共享，chroot 本身运行在内核态，需要 root 权限</p><p>小结:</p><ol type="1"><li>对于没有 Root 权限的 Android 设备，使用 Termux+proot 方式安装完整 linux 是最佳方案，proot 是用户空间的 chroot,系统调用会拦截一层，有一些性能损失，但是这种隔离远不如容器的隔离，性能损失比较小，是完全可以接受的 参考: <a href="https://wiki.termux.com/wiki/Main_Page">Termux Wiki</a></li><li> 对于有 Root 权限的 Android 设备，使用 LinuxDeploy (<a href="https://github.com/lateautumn233/Linuxdeploy-Pro">LinuxDeploy-Pro</a>原作者 meefik 的 github 库貌似已经没有更新，且安装时有一些问题),LinuxDeploy 使用 Chroot 实现，需要 Root 权限，相对于 Proot,其系统调用没有转换操作，性能更好，适合长期运行</li></ol><h2 id="前置准备">2 前置准备</h2><ol type="1"><li><p>bootloader 解锁</p></li><li><p>驱动安装，小米手机可以用 miflash 安装驱动</p></li><li><p>解决 Windows 上 usb3 使用 fastboot 时卡住的问题</p><p></p><figure class="highlight bat"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">@<span class="built_in">echo</span> off</span><br><span class="line">reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\usbflags\<span class="number">18</span>D1D00D0100" /v "osvc" /t REG_BINARY /d "<span class="number">0000</span>" /f</span><br><span class="line">reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\usbflags\<span class="number">18</span>D1D00D0100" /v "SkipContainerIdQuery" /t REG_BINARY /d "<span class="number">01000000</span>" /f</span><br><span class="line">reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\usbflags\<span class="number">18</span>D1D00D0100" /v "SkipBOSDescriptorQuery" /t REG_BINARY /d "<span class="number">01000000</span>" /f</span><br><span class="line"></span><br><span class="line"><span class="built_in">pause</span></span><br></pre></td></tr></tbody></table></figure><p></p></li><li><p>(刷系统为可选项) 系统刷为 LineageOS 参考:https://wiki.lineageos.org/devices/sagit/install</p></li><li><p> 刷入 twrp, 参考: https://twrp.me/xiaomi/xiaomimi6.html, img 下载:https://dl.twrp.me/sagit/</p><ul><li><code>fastboot flash recovery ./twrp-xxx.img</code></li></ul></li><li><p>刷入 magisk (可以先刷入 twrp, 参考 https://dl.twrp.me/sagit/)https://github.com/topjohnwu/Magisk</p><ul><li>下载最新的 magisk apk 文件，后缀改为 zip</li><li> 在 twrp 中选择对应的 zip 文件刷入，如果是 LineageOS 的 recovery,可以适用 adb sideload 刷入</li><li>重启后打开 magisk, 按照提示进行后续操作，按推荐步骤执行即可</li></ul></li><li><p>给 shell 赋予 root 权限，打开开发者模式，打开 USB 调试，打开 USBroot 调试</p><ul><li><code>adb shell</code> 连接手机</li><li><code>su</code> 如果执行失败，去 magisk 的 root 权限管理中打开com.android.shell 包的 root 权限</li><li>再次尝试 <code>su</code></li></ul></li></ol><h2 id="linuxdeploy安装部署和配置">3 LinuxDeploy 安装部署和配置</h2><ol type="1"><li><p>LinuxDeploy 应用安装</p><ul><li>官方的 <a href="https://github.com/meefik/linuxdeploy">LinuxDeploy</a>,可以先尝试一下，小米 6 使用官网的 app 一直安装有问题，所以最终没有使用官方的 apk</li><li> 我的小米 6 使用 <a href="https://github.com/lateautumn233/Linuxdeploy-Pro">LinuxDeploy-Pro</a>,看维护时间还比较新，官方地址貌似停止维护了</li><li>下载 apk 安装，打开时授予 root 权限</li></ul></li><li><p> LinuxDeploy 配置</p><p>应用右下角按钮设置安装选项，这里列一下我的选择，可以根据喜好或者实际安装情况决定</p><ul><li>chroot 不用改</li><li> Debian</li><li>arm64</li><li>stable</li><li>http://mirrors.ustc.edu.cn/debian小米 6 这里设置 <strong>https 连不上</strong> , 只有 http 能用</li><li> file</li><li><code>${EXETERNAL_STORAGE}/debian.img</code></li><li>81920 镜像大小我给了 80G, 开始只给 10G, 后面软件安装发现不够用了，不过之后也可以扩容，只是费时间</li><li> ext4 不用改</li><li>用户名和密码自由设置</li><li> en_US.UTF-8</li><li>Auto DNS 设置可以改为好用的地址，我这里选的自动</li><li>勾选 INIT, 小米 6 上 run-parts 我没有调教好，这里选的<strong>sysv</strong>, 用于开启容器时自动执行一些任务</li><li>勾选 MOUNTS, <code>/sdcard:/sdcard</code>主要是将安卓内部存储挂载到 Linux 系统内</li><li>勾选 SSH, 该步骤是必须的，否则安装的 Linux 不好访问</li></ul></li><li><p>部署 Linux</p><p>按照上述配置完成后，返回主界面，点击右上 "三点", 选择 "install",开始安装部署</p><ul><li>若提示联网问题，先检查设备是否联网，镜像配置是否正确，是否使用 http 协议</li><li>更改配置后，先点 stop 按钮卸载分区，之后再次点 install 安装</li><li>安装过程必须保证没有报错，若有报错，可能需要搜索相关问题，解决后重新安装</li><li>若使用该方法怎样都安装不成功，可以参考 ((20230730133322-tx8cs9x' 备份与恢复 ')) 一节的方法，直接导入合适架构的备份包即可</li></ul></li><li><p>启动容器，ssh 连接</p><ul><li>点击 start 即可启动容器</li><li>启动成功后可以通过 ssh 连接到 Linux</li><li> 可以局域网的 PC 通过 IP 连接</li><li>也可以手机上安装 JuiceSSH, 通过 localhost 或者 127.0.0.1 连接</li><li>启动容器后，最好 sudo su 切<strong>换到 root 用户</strong>操作，之后所有操作都基于 root 用户</li></ul></li><li><p>开机自启动，CPU 锁，Wi-Fi 锁</p><p>打开 LinuxDeploy 左上角菜单</p><ul><li>Lock Wi-Fi 应用运行时保持 WiFi 打开</li><li> Wake lock 应用运行时保持 CPU 运转，即使锁屏</li><li> Autostart 当 Android 启动后自动运行应用，并运行默认配置的容器，非常有用</li><li> Autostart delay 自启动延时 我设置了 10 秒</li></ul></li><li><p>备份与恢复</p><p>Telnet 服务: LinuxDeploy 左上角菜单设置，Services, TELNET 和 HTTP 都打开，取消勾选 TELNET 中的 Localhost, HTTP 服务的 Accessrestriction 中 A 之后设置允许连接的 IP 地址比如 <code>A:192.168.31.27 D:*</code></p><p>这里的 HTTP 服务是由 httpd 提供，支持配置多个 <code>A:xxx</code> 添加多个可以访问的 IP 地址</p><p>浏览器访问 <code>http://ip:5080</code> 打开 Linux DeployTerminal 的 Telnet 终端</p><ul><li><p>备份与恢复命令</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">su <span class="comment"># 切换为root</span></span><br><span class="line"><span class="built_in">cd</span> /sdcard</span><br><span class="line">linuxdeploy stop -u <span class="comment"># 停止容器并卸载分区</span></span><br><span class="line">linuxdeploy <span class="built_in">export</span> /sdcard/debian-rootfs-20230729.tgz <span class="comment"># 等待完成即可, 之后可以拷贝一份到电脑上</span></span><br><span class="line">linuxdeploy import /sdcard/debian-rootfs-20230729.tgz <span class="comment"># 导入操作</span></span><br><span class="line">linuxdeploy start <span class="comment"># 运行容器</span></span><br></pre></td></tr></tbody></table></figure></li><li><p>如果上述的安装不成功，也可以下载合适架构的备份包，直接导入[小米 6 的架构为 arm64 (aarch64)]</p><ul><li>ubuntu 18 LTS arm64(http://hub.meefik.ru/rootfs/ubuntu_arm64.tgz)</li><li>debian 10 arm64 (http://hub.meefik.ru/rootfs/debian_arm64.tgz)</li></ul></li></ul></li><li><p> 镜像扩容</p><p>先打开 telnet 访问，切 root 用户</p><p></p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># 从/dev/zero取二进制0, 块大小为1M, 一共4096个块, 追加到debian.img (扩容4GB)</span></span><br><span class="line"><span class="built_in">dd</span> <span class="keyword">if</span>=/dev/zero bs=1048576 count=4096 >> /sdcard/debian.img</span><br><span class="line"></span><br><span class="line"><span class="comment"># 强制检查(修复)镜像的硬盘分区</span></span><br><span class="line">e2fsck -f /sdcard/debian.img</span><br><span class="line"></span><br><span class="line"><span class="comment"># 调整分区大小, 同步文件系统容量?</span></span><br><span class="line">resize2fs /sdcard/debian.img</span><br></pre></td></tr></tbody></table></figure><p></p></li><li><p>LinuxDeploy 中的一些限制</p><ul><li>不是基于 systemd 运行的，systemctl, service 等命令无法正常工作</li><li>不支持 docker, 如果想要支持，需要自己编译 android 内核，修改编译选项，相当麻烦</li></ul></li></ol><h2 id="linux系统配置">4 Linux 系统配置</h2><p>我的小米 6 系统部署启动成功后，发现 ssh 连接正常，apt 更新也正常，但是 ping 不通任何域名和地址，包括 127.0.0.1,curl 和 wget 等应用也无法使用</p><ol type="1"><li><p>解决联网问题 尝试了很多方法，只能让 root 用户正常联网</p><ul><li><p>编辑 <code>/etc/group</code> 在 aid_inet (3003),aid_net_raw (3004) 的分组中添加需要的用户名，多个用户名用逗号分开</p><figure class="highlight plaintext"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">aid_inet:x:3003:fetasty,root</span><br><span class="line">aid_net_raw:x:3004:fetasty,root</span><br></pre></td></tr></tbody></table></figure></li></ul></li><li><p>解决 ssh 连接后，无法 tab 补全，无法查看历史命令，没有颜色显示问题</p><ul><li><p>编辑 /etc/passwd 在对应用户名后将 sh 更改为 bash</p><figure class="highlight plaintext"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">fetasty:x:60000:60000::/home/fetasty:/bin/bash</span><br></pre></td></tr></tbody></table></figure></li><li><p>编辑～/.bashrc 取消注释其中要显示颜色的行</p><figure class="highlight plaintext"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">source ~/.bashrc</span><br></pre></td></tr></tbody></table></figure></li></ul></li><li><p>supervisor 自启动服务配置 (chroot 中的 Linux, systemd, systemctl,service 等命令并不好用，不好设置自启动)</p><p>这里我们使用 <a href="http://supervisord.org/">supervisor</a> 管理其余服务进程，主要设置好 supervisor 自启动和配置</p><ul><li><p><code>apt-get install supervisor</code> 安装 supervisor,用于管理自启动进程 (按照官网的意思，应该使用 pip 安装，但是我实际使用时并不太顺利)</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">cd</span> ~</span><br><span class="line"><span class="comment"># curl -O https://bootstrap.pypa.io/get-pip.py</span></span><br><span class="line"><span class="comment"># python3 get-pip.py # 运行失败, 安装pip失败, 提示应该使用apt install python3-xxx来安装</span></span><br><span class="line">apt install python3-pip <span class="comment"># 安装成功</span></span><br><span class="line">pip3 config <span class="built_in">set</span> global.index-url https://pypi.mirrors.ustc.edu.cn/simple</span><br><span class="line">pip3 config list</span><br><span class="line"><span class="comment"># pip3 install supervisor # 失败 https://stackoverflow.com/questions/75608323/how-do-i-solve-error-externally-managed-environment-everytime-i-use-pip3</span></span><br><span class="line">pip3 install supervisor --break-system-packages <span class="comment"># 命令行提示最好先venv创建一个环境再安装, 太麻烦了, 不如apt直接装</span></span><br></pre></td></tr></tbody></table></figure></li><li><p>确认容器启动配置中为 <strong>sysv</strong>,小米 6 上测试了 run-parts 方式的自启动无效 参考 <a href="https://blog.csdn.net/qq_43445867/article/details/131799629">LinuxDeploy 应用自启动</a></p></li><li><p><code>~~nano /etc/init.d/supervisord.sh~~</code> ~~编辑 supervisord 应用的启动脚本，该脚本必须按照<del><a href="https://wiki.debian.org/LSBInitScripts"><del>规范</del></a></del>编写～～</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#!/bin/sh</span></span><br><span class="line"></span><br><span class="line"><span class="comment">### BEGIN INIT INFO</span></span><br><span class="line"><span class="comment"># Provides: supervisord</span></span><br><span class="line"><span class="comment"># Required-Start: $network $remote_fs $local_fs</span></span><br><span class="line"><span class="comment"># Required-Stop: $network $remote_fs $local_fs</span></span><br><span class="line"><span class="comment"># Default-Start: 2 3 4 5</span></span><br><span class="line"><span class="comment"># Default-Stop: 0 1 6</span></span><br><span class="line"><span class="comment"># Short-Description: supervisord start</span></span><br><span class="line"><span class="comment"># Description: supervisord run script</span></span><br><span class="line"><span class="comment">### END INIT INFO</span></span><br><span class="line"></span><br><span class="line">/usr/bin/supervisord -c /etc/supervisor/supervisord.conf</span><br><span class="line"></span><br><span class="line"><span class="built_in">exit</span> 0</span><br></pre></td></tr></tbody></table></figure><ul><li><code>chmod +x /etc/init.d/supervisord.sh</code> 赋予执行权限</li><li><code>update-rc.d supervisord.sh defaults</code> 设置开机自启动</li><li><code>update-rc.d -f supervisord.sh remove</code>移除开机自启动</li></ul></li><li><p>后续发现 apt 安装 supervisor 后，<code>/etc/init.d</code>目录下存在一个 supervisor 文件，但是并未成功自启动(lighttpd 安装后可正常自启动)</p><ol type="1"><li><p>给该文件添加运行权限</p></li><li><p>该文件前面有一段注释，不知道是否符合<a href="https://wiki.debian.org/LSBInitScripts">规范</a> , 删除了<code>### BEGIN INIT INFO</code> 之前的一段注释</p></li><li><p>执行 update-rc.d 命令</p><p></p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">update-rc.d supervisor defaults</span><br><span class="line">update-rc.d supervisor <span class="built_in">enable</span></span><br></pre></td></tr></tbody></table></figure><p></p></li></ol></li><li><p>supervisor <a href="http://supervisord.org/installing.html#creating-a-configuration-file">配置生成</a><a href="http://supervisord.org/configuration.html">配置说明</a></p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">echo_supervisord_conf > /etc/supervisor/supervisord.conf <span class="comment"># 生成配置模板</span></span><br></pre></td></tr></tbody></table></figure><p>修改配置，小米 6 上的 supervisord 使用 sock 文件一直有报错，我修改成了 http 方式，注释了 unix_http_server 部分，打开了 inet_http_server 部分 (可能与之前的分组有同样关系？)</p><figure class="highlight ini"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">;[unix_http_server]</span></span><br><span class="line"><span class="comment">;file=/tmp/supervisor.sock ; the path to the socket file</span></span><br><span class="line"><span class="comment">;chmod=0777 ; socket file mode (default 0700)</span></span><br><span class="line"><span class="comment">;chown=root:root ; socket file uid:gid owner</span></span><br><span class="line"><span class="comment">;username=user ; default is no username (open server)</span></span><br><span class="line"><span class="comment">;password=123 ; default is no password (open server)</span></span><br><span class="line"></span><br><span class="line"><span class="section">[inet_http_server]</span> <span class="comment">; inet (TCP) server disabled by default</span></span><br><span class="line"><span class="attr">port</span>=*:<span class="number">9001</span> <span class="comment">; ip_address:port specifier, *:port for all iface</span></span><br><span class="line"><span class="comment">;username=user ; default is no username (open server)</span></span><br><span class="line"><span class="comment">;password=123 ; default is no password (open server)</span></span><br><span class="line"></span><br><span class="line"><span class="section">[supervisorctl]</span></span><br><span class="line"><span class="comment">;serverurl=unix:///tmp/supervisor.sock ; use a unix:// URL for a unix socket</span></span><br><span class="line"><span class="attr">serverurl</span>=http://<span class="number">127.0</span>.<span class="number">0.1</span>:<span class="number">9001</span> <span class="comment">; use an http:// url to specify an inet socket</span></span><br><span class="line"></span><br><span class="line"><span class="section">[include]</span></span><br><span class="line"><span class="attr">files</span> = /etc/supervisor/conf.d/*.conf</span><br></pre></td></tr></tbody></table></figure></li><li><p>设置好 supervisor 的自启动后，stop 再 start,看命令行中是否有 supervisor 的运行提示，若设置成功，其余需要自启动的进程就可以交给 supervisor 来管理</p></li><li><p> supervisord 服务启动后，会监听 9001 端口，用于控制和查看进程的状态</p></li><li><p>添加新的进程配置文件后 执行 <code>supervisorctl reload</code>刷新，再访问 9001 的 http 服务，就可以查看进程状态</p></li><li><p><code>supervisorctl reload</code> 命令会重启所有管理的进程，如果只是加载新添加的配置可以运行以下指令</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">supervisorctl reread <span class="comment"># 重新读取配置文件</span></span><br><span class="line">supervisorctl update <span class="comment"># 刷新配置到进程组</span></span><br></pre></td></tr></tbody></table></figure><p>之后可以在 supervisor 管理页面看到对应的进程配置</p></li><li><p>如果需要配置多个环境变量，可以在 Environment 字段这样填写</p><figure class="highlight ini"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="attr">environment</span>=KEY=<span class="string">"val:123"</span>,KEY2=<span class="string">"val,456"</span></span><br></pre></td></tr></tbody></table></figure></li></ul></li></ol><p>常用命令</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line">free -h <span class="comment"># 查看内存占用</span></span><br><span class="line">top <span class="comment"># 查看资源占用最多的进程</span></span><br><span class="line">ps aux <span class="comment"># 查看进程列表</span></span><br><span class="line">ip addr <span class="comment"># 查看ip</span></span><br><span class="line">ss -anptu <span class="comment"># t(tcp) u(udp) 查看网络连接</span></span><br><span class="line"><span class="built_in">df</span> -h <span class="comment"># 查看磁盘空间</span></span><br><span class="line"><span class="built_in">du</span> -h --max-depth=1 /home <span class="comment"># 查看某个文件夹下的各文件/文件夹大小统计</span></span><br><span class="line"><span class="comment"># 查看用户信息 (uid, 所在分组) 用户需要在3003,3004分组中才具有网络访问权限</span></span><br><span class="line"><span class="built_in">id</span> [username]</span><br><span class="line"><span class="comment"># 编辑文件 ctrl-x ctrl-k alt-u alt-e</span></span><br><span class="line">nano /etc/apt/source.list</span><br><span class="line"><span class="comment"># 编辑用户组信息</span></span><br><span class="line">nano /etc/group</span><br><span class="line">passwd <span class="comment"># 设置当前用户密码</span></span><br><span class="line"><span class="built_in">chmod</span> a+rx xxx.sh <span class="comment"># a </span></span><br></pre></td></tr></tbody></table></figure><h2 id="常用软件">5 常用软件</h2><h3 id="lighttpd-轻量web服务">5.1 lighttpd 轻量 Web 服务</h3><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">apt install lighttpd</span><br></pre></td></tr></tbody></table></figure><p>安装完成后已经自动在 /etc/init.d 目录下创建自启动配置，运行配置在 <code>/etc/lighttpd/lighttpd.conf</code>,默认网站路径为 <code>/var/www/html/</code></p><p>默认配置我没有改动，监听 80 端口，主要用于展示一个所有服务的导航页面，因为且换网络环境时服务器 IP 会变，想弄个方便的导航页，根据 hostname 值自动调整导航链接</p><ul><li><p>index.html 源码，使用 bootstrap 稍微修饰了一下，其实没啥必要</p><figure class="highlight html"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta"><!doctype <span class="keyword">html</span>></span></span><br><span class="line"><span class="tag"><<span class="name">html</span> <span class="attr">lang</span>=<span class="string">"en-US"</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">head</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">meta</span> <span class="attr">charset</span>=<span class="string">"utf-8"</span> /></span></span><br><span class="line"> <span class="tag"><<span class="name">meta</span> <span class="attr">name</span>=<span class="string">"viewport"</span> <span class="attr">content</span>=<span class="string">"width=device-width, initial-scale=1"</span> /></span></span><br><span class="line"> <span class="tag"><<span class="name">link</span> <span class="attr">rel</span>=<span class="string">"shortcut icon"</span> <span class="attr">href</span>=<span class="string">"#"</span> /></span></span><br><span class="line"> <span class="tag"><<span class="name">title</span>></span>Services List<span class="tag"></<span class="name">title</span>></span></span><br><span class="line"> <span class="tag"></<span class="name">head</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">body</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">div</span> <span class="attr">class</span>=<span class="string">"container"</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">h1</span>></span>Services List<span class="tag"></<span class="name">h1</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">div</span> <span class="attr">id</span>=<span class="string">"services"</span> <span class="attr">class</span>=<span class="string">"list-group"</span>></span></span><br><span class="line"> <span class="tag"></<span class="name">div</span>></span></span><br><span class="line"> <span class="tag"></<span class="name">div</span>></span></span><br><span class="line"> </span><br><span class="line"> <span class="tag"><<span class="name">script</span>></span><span class="language-javascript"></span></span><br><span class="line"><span class="language-javascript"> <span class="keyword">let</span> services = [</span></span><br><span class="line"><span class="language-javascript"> [<span class="string">"Supervisor"</span>, <span class="number">9001</span>, <span class="string">""</span>],</span></span><br><span class="line"><span class="language-javascript"> [<span class="string">"Siyuan"</span>, <span class="number">6806</span>, <span class="string">""</span>],</span></span><br><span class="line"><span class="language-javascript"> [<span class="string">"Cloudreve"</span>, <span class="number">5212</span>, <span class="string">""</span>],</span></span><br><span class="line"><span class="language-javascript"> [<span class="string">"Cloudreve Admin"</span>, <span class="number">5212</span>, <span class="string">"/admin"</span>],</span></span><br><span class="line"><span class="language-javascript"> [<span class="string">"V2raya"</span>, <span class="number">2017</span>, <span class="string">""</span>]</span></span><br><span class="line"><span class="language-javascript"> ];</span></span><br><span class="line"><span class="language-javascript"> <span class="keyword">let</span> container = <span class="variable language_">document</span>.<span class="title function_">querySelector</span>(<span class="string">"#services"</span>);</span></span><br><span class="line"><span class="language-javascript"> <span class="keyword">let</span> hostname = <span class="variable language_">window</span>.<span class="property">location</span>.<span class="property">hostname</span>;</span></span><br><span class="line"><span class="language-javascript"> <span class="keyword">let</span> content = <span class="string">""</span>;</span></span><br><span class="line"><span class="language-javascript"> services.<span class="title function_">forEach</span>(<span class="function">(<span class="params">service</span>) =></span> {</span></span><br><span class="line"><span class="language-javascript"> content += <span class="string">"<a class=\"list-group-item list-group-item-action\" "</span></span></span><br><span class="line"><span class="language-javascript"> + <span class="string">"target=\"_blank\" "</span></span></span><br><span class="line"><span class="language-javascript"> + <span class="string">"href=\"http://"</span></span></span><br><span class="line"><span class="language-javascript"> + hostname + <span class="string">":"</span></span></span><br><span class="line"><span class="language-javascript"> + service[<span class="number">1</span>]</span></span><br><span class="line"><span class="language-javascript"> + service[<span class="number">2</span>]</span></span><br><span class="line"><span class="language-javascript"> + <span class="string">"\">"</span></span></span><br><span class="line"><span class="language-javascript"> + service[<span class="number">0</span>]</span></span><br><span class="line"><span class="language-javascript"> + <span class="string">"</a>\n"</span>;</span></span><br><span class="line"><span class="language-javascript"> })</span></span><br><span class="line"><span class="language-javascript"> container.<span class="property">innerHTML</span> = content;</span></span><br><span class="line"><span class="language-javascript"> </span><span class="tag"></<span class="name">script</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">link</span> <span class="attr">href</span>=<span class="string">"/bootstrap.min.css"</span> <span class="attr">rel</span>=<span class="string">"stylesheet"</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">script</span> <span class="attr">src</span>=<span class="string">"/bootstrap.bundle.min.js"</span>></span><span class="tag"></<span class="name">script</span>></span></span><br><span class="line"> <span class="tag"></<span class="name">body</span>></span></span><br><span class="line"><span class="tag"></<span class="name">html</span>></span></span><br></pre></td></tr></tbody></table></figure></li></ul><h3 id="开发编译环境">5.2 开发编译环境</h3><ol type="1"><li><p>rust 最好开代理安装 参考<a href="https://www.rust-lang.org/tools/install">官网安装说明</a>(可以参考字节镜像源中的说明安装，无需代理)</p><p></p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">curl --proto <span class="string">'=https'</span> --tlsv1.2 -sSf https://sh.rustup.rs | sh</span><br></pre></td></tr></tbody></table></figure><p></p><p>设置 cargo 镜像源 这里使用<a href="http://rsproxy.cn/#getStarted">字节镜像源</a> ,其实安装也可以参考这里，还可以加快安装速度</p><p>编辑 <code>$HOME/.cargo/config</code></p><p></p><figure class="highlight ini"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="section">[source.crates-io]</span></span><br><span class="line"><span class="attr">replace-with</span> = <span class="string">'rsproxy-sparse'</span></span><br><span class="line"><span class="section">[source.rsproxy]</span></span><br><span class="line"><span class="attr">registry</span> = <span class="string">"https://rsproxy.cn/crates.io-index"</span></span><br><span class="line"><span class="section">[source.rsproxy-sparse]</span></span><br><span class="line"><span class="attr">registry</span> = <span class="string">"sparse+https://rsproxy.cn/index/"</span></span><br><span class="line"><span class="section">[registries.rsproxy]</span></span><br><span class="line"><span class="attr">index</span> = <span class="string">"https://rsproxy.cn/crates.io-index"</span></span><br><span class="line"><span class="section">[net]</span></span><br><span class="line"><span class="attr">git-fetch-with-cli</span> = <span class="literal">true</span></span><br></pre></td></tr></tbody></table></figure><p></p></li><li><p>golang 参考<a href="https://go.dev/doc/install">官方文档</a> ,下载压缩包之后运行对应命令安装 (apt 直接安装的无法正常使用)</p><ul><li>在 <code>$HOME/.bashrc</code> 中添加<code>export PATH="$PATH:/usr/local/go/bin"</code></li></ul></li><li><p>缓存清理方法 (备份系统前最好先清理缓存)</p><ul><li>golang 清理缓存 <code>go clean -cache</code><code>go clean -modcache</code> 可以极大减小 <code>$HOME/go</code>目录大小</li><li> cargo 清理缓存 安装 cargo-cache, 运行 cargo-cache, .rustup目录貌似无法精简</li><li> yarn 清理缓存 <code>yarn cache clean</code>极大减小 <code>/usr/local/share/.cache/yarn</code> 目录大小</li></ul></li></ol><h3 id="cloudreve-网盘">5.3 cloudreve 网盘</h3><p>官网下载 arm64 版本二进制运行文件https://github.com/cloudreve/Cloudreve</p><p>创建 <code>/etc/supervisor/conf.d/cloudreve.conf</code></p><figure class="highlight ini"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="section">[program:cloudreve]</span></span><br><span class="line"><span class="attr">directory</span>=/home/cloudreve</span><br><span class="line"><span class="attr">command</span>=/home/cloudreve/cloudreve</span><br><span class="line"><span class="attr">autostart</span>=<span class="literal">true</span></span><br><span class="line"><span class="attr">autorestart</span>=<span class="literal">true</span></span><br><span class="line"><span class="attr">stderr_logfile</span>=/var/log/cloudreve.err</span><br><span class="line"><span class="attr">stdout_logfile</span>=/var/log/cloudreve.log</span><br><span class="line"><span class="attr">environment</span>=CODENATION_ENV=prod</span><br></pre></td></tr></tbody></table></figure><h3 id="siyuan-笔记">5.4 siyuan 笔记</h3><p><strong>后端 core 程序编译</strong></p><p>siyuan 笔记我只想使用后端服务，使用浏览器访问，但是官方只提供 docker 方式的服务端部署方式，且只提供了 linux amd64 的包，需要自己编译</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">cd</span> /home</span><br><span class="line">git <span class="built_in">clone</span> https://github.com/siyuan-note/siyuan.git</span><br><span class="line"><span class="built_in">cd</span> siyuan</span><br><span class="line">git checkout vx.x.x <span class="comment"># 切换到对应版本号</span></span><br></pre></td></tr></tbody></table></figure><p>修改 <code>scripts/linux-build.sh</code> 编译脚本</p><p>编译 siyuan-kernel, 其中的 GOARCH 需要从 amd64 改为 arm64,goproxy 可以更改为 <code>https://goproxy.cn</code></p><p>执行 <code>scripts/linux-build.sh</code>, 编译内核</p><p>官网下载对应版本号的 linux.tar.gz,解压后将 kernel 目录中的 siyuan-kernel 文件替换为我们自己编译生成的二进制文件</p><p>创建 <code>/etc/supervisor/conf.d/siyuan.conf</code> 其中的 <code>RUN_IN_CONTAINER</code> 环境变量配置非常重要，否则它默认以为是客户端模式运行，会定时检测 Electron 前端程序是否存在，若不存在，则一定时间后自动退出</p><figure class="highlight ini"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="section">[program:siyuan]</span></span><br><span class="line"><span class="attr">directory</span>=/home/siyuan</span><br><span class="line"><span class="attr">command</span>=/home/siyuan/kernel/siyuan-kernel -lang zh_CN -wd /home/siyuan -workspace /root/siyuan</span><br><span class="line"><span class="attr">autostart</span>=<span class="literal">true</span></span><br><span class="line"><span class="attr">autorestart</span>=<span class="literal">true</span></span><br><span class="line"><span class="attr">stderr_logfile</span>=/var/log/siyuan.err</span><br><span class="line"><span class="attr">stdout_logfile</span>=/var/log/siyuan.log</span><br><span class="line"><span class="attr">environment</span>=RUN_IN_CONTAINER=<span class="number">1</span></span><br></pre></td></tr></tbody></table></figure><p><strong>前端资源编译</strong></p><p>安装 nodejs, 去官网看看<a href="https://nodejs.org/en/download/package-manager">包管理器安装方法</a> ,提示 Debian 的安装可以按照以下方式进行 (参考:https://github.com/nodesource/distributions)</p><ol type="1"><li><p>Download and import the Nodesource GPG key</p><p></p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">sudo apt-get update</span><br><span class="line">sudo apt-get install -y ca-certificates curl gnupg</span><br><span class="line">sudo <span class="built_in">mkdir</span> -p /etc/apt/keyrings</span><br><span class="line">curl -fsSL https://deb.nodesource.com/gpgkey/nodesource-repo.gpg.key | sudo gpg --dearmor -o /etc/apt/keyrings/nodesource.gpg</span><br></pre></td></tr></tbody></table></figure><p></p></li><li><p>Create deb repository (<code>NODE_MAJOR</code> can be changeddepending on the version you need.) 16, 18, 20</p><p></p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">NODE_MAJOR=20</span><br><span class="line"><span class="built_in">echo</span> <span class="string">"deb [signed-by=/etc/apt/keyrings/nodesource.gpg] https://deb.nodesource.com/node_<span class="variable">$NODE_MAJOR</span>.x nodistro main"</span> | sudo <span class="built_in">tee</span> /etc/apt/sources.list.d/nodesource.list</span><br></pre></td></tr></tbody></table></figure><p></p></li><li><p>Run Update and Install</p><p></p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">sudo apt-get update</span><br><span class="line">sudo apt-get install nodejs -y</span><br></pre></td></tr></tbody></table></figure><p></p></li><li><p>Uninstall</p><p></p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">apt-get purge nodejs &&\</span><br><span class="line"><span class="built_in">rm</span> -r /etc/apt/sources.list.d/nodesource.list &&\</span><br><span class="line"><span class="built_in">rm</span> -r /etc/apt/keyrings/nodesource.gpg</span><br></pre></td></tr></tbody></table></figure><p></p></li></ol><p>我选择了安装 18 的 LTS 版本</p><p>设置 npm 镜像源 (后面两个提示不支持，按照下一步操作)</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># 设置阿里镜像</span></span><br><span class="line">npm config <span class="built_in">set</span> registry=https://registry.npmmirror.com</span><br><span class="line">npm config <span class="built_in">set</span> disturl=https://registry.npmmirror.com/-/binary/node</span><br><span class="line"></span><br><span class="line"><span class="comment"># 设置electron仓库</span></span><br><span class="line">npm config <span class="built_in">set</span> electron_mirror=https://registry.npmmirror.com/-/binary/electron/</span><br></pre></td></tr></tbody></table></figure><p>设置失败可以直接修改文件 <code>nano ~/.npmrc</code></p><figure class="highlight plaintext"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">registry=https://registry.npmmirror.com</span><br><span class="line">disturl=https://registry.npmmirror.com/-/binary/node</span><br><span class="line">electron_mirror=https://registry.npmmirror.com/-/binary/electron/</span><br></pre></td></tr></tbody></table></figure><p>安装 yarn, pnpm</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">npm install -g yarn</span><br><span class="line">npm install -g pnpm</span><br></pre></td></tr></tbody></table></figure><p>在 siyuan 根目录运行<code>./scripts/linux-build.sh</code> 即可</p><h3 id="v2raya-代理">5.5 v2raya 代理</h3><p>安装 v2raya 参考<a href="https://v2raya.org/docs/prologue/installation/debian/">官方文档</a></p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># 添加软件源安装</span></span><br><span class="line">wget -qO - https://apt.v2raya.org/key/public-key.asc | sudo <span class="built_in">tee</span> /etc/apt/trusted.gpg.d/v2raya.asc</span><br><span class="line"><span class="built_in">echo</span> <span class="string">"deb https://apt.v2raya.org/ v2raya main"</span> | sudo <span class="built_in">tee</span> /etc/apt/sources.list.d/v2raya.list</span><br><span class="line">sudo apt update</span><br><span class="line">sudo apt install v2raya</span><br></pre></td></tr></tbody></table></figure><p>下载 <a href="https://github.com/v2fly/v2ray-core">v2fly/v2ray-core</a>v2ray-linux-arm64-v8a</p><p>编辑 <code>/etc/supervisor/conf.d/v2raya.conf</code> 其中的<code>--v2ray-bin</code> 选项用于配置 v2ray-core 文件路径</p><figure class="highlight ini"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="section">[program:v2raya]</span></span><br><span class="line"><span class="attr">directory</span>=/usr/bin</span><br><span class="line"><span class="attr">command</span>=/usr/bin/v2raya --v2ray-bin /home/v2ray/v2ray</span><br><span class="line"><span class="attr">autostart</span>=<span class="literal">false</span></span><br><span class="line"><span class="attr">autorestart</span>=<span class="literal">true</span></span><br><span class="line"><span class="attr">stderr_logfile</span>=/var/log/v2raya.err</span><br><span class="line"><span class="attr">stdout_logfile</span>=/var/log/v2raya.log</span><br><span class="line"><span class="attr">environment</span>=V2RAYA_LOG_FILE=/var/log/v2raya/v2raya.log</span><br></pre></td></tr></tbody></table></figure><p>这里没有设置为自启动，根据需求配置</p><p>打开进程后默认监听 2017 端口，访问可以配置选项，"port sharing" 打开后，可以将代理端口共享到局域网中，供其他设备使用</p><h3 id="code-server">5.6 code-server</h3><p>自部署，可以通过浏览器访问的 VS Code</p><p>安装参考<a href="https://github.com/coder/code-server/tree/main#getting-started">官方文档</a></p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">export</span> http_proxy=http://xxxx:xxx</span><br><span class="line"><span class="built_in">export</span> https_proxy=<span class="variable">$http_proxy</span></span><br><span class="line">curl -fsSL https://code-server.dev/install.sh | sh</span><br></pre></td></tr></tbody></table></figure><p>使用方式参考<a href="https://github.com/coder/code-server/blob/main/docs/guide.md#expose-code-server">官方文档</a></p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># Replaces "auth: password" with "auth: none" in the code-server config.</span></span><br><span class="line">sed -i.bak <span class="string">'s/auth: password/auth: none/'</span> ~/.config/code-server/config.yaml</span><br></pre></td></tr></tbody></table></figure><p>编辑 <code>/etc/supervisor/conf.d/code-server.conf</code></p><figure class="highlight ini"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="section">[program:code-server]</span></span><br><span class="line"><span class="attr">directory</span>=/usr/bin</span><br><span class="line"><span class="attr">command</span>=/usr/bin/code-server</span><br><span class="line"><span class="attr">autostart</span>=<span class="literal">false</span></span><br><span class="line"><span class="attr">autorestart</span>=<span class="literal">true</span></span><br><span class="line"><span class="attr">stderr_logfile</span>=/var/log/code-server.err</span><br><span class="line"><span class="attr">stdout_logfile</span>=/var/log/code-server.log</span><br><span class="line">environment=</span><br></pre></td></tr></tbody></table></figure><p>暴露服务端口，这部分最简单的方式是按照官方提示，使用 SSH Forwarding,不然比较麻烦，直接暴露 HTTP 端口，使用会提示不安全，且很多功能会失效</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># -N disables executing a remote shell</span></span><br><span class="line">ssh -N -L 8080:127.0.0.1:8080 [user]@<instance-ip></span><br><span class="line"><span class="comment"># ssh -N -L 8080:127.0.0.1:8080 [email protected]</span></span><br></pre></td></tr></tbody></table></figure><h2 id="cpu调度问题探究">6 CPU 调度问题探究</h2><p>使用 lineageos 时关闭屏幕会自动开启 doze 模式，目前只能是 usb 默认文件传输，接上电脑使用 [或者刷系统看看，honor v10 没有刷 lineageos 没有该问题]</p><p><strong>刷回小米的 MIUI 系统并禁用一部分系统应用，效果还可以</strong></p><p>以下内容是探索该问题的一些思路历程</p><p>问题定位:https://blog.csdn.net/wenzhi20102321/article/details/130977176</p><p>查看安卓日志</p><figure class="highlight plaintext"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">adb shell</span><br><span class="line">logcat -c # 先清空日志</span><br><span class="line"># 进行操作，拔掉电源线，关闭屏幕</span><br><span class="line"># 再连接usb线，打开adb shell</span><br><span class="line">logcat threadtime | grep -i -E "Wifi|Power" # 查看和电源与wifi相关的日志</span><br></pre></td></tr></tbody></table></figure><p>注意到以下日志</p><figure class="highlight plaintext"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line">09-28 22:22:47.166 1664 1664 I FingerprintManager: onPowerPressed</span><br><span class="line">09-28 22:22:47.167 1664 1664 I PowerManagerService: Going to sleep due to power_button (uid 1000, screenOffTimeout=60000, activityTimeoutWM=-1, maxDimRatio=0.20000005, maxDimDur=7000)...</span><br><span class="line">09-28 22:22:47.670 976 976 D SurfaceFlinger: Setting power mode 0 on display 0</span><br><span class="line">09-28 22:22:47.848 976 976 D SurfaceFlinger: Finished setting power mode 0 on display 0</span><br><span class="line">09-28 22:22:47.850 1664 2267 D SurfaceControl: Excessive delay in setPowerMode()</span><br><span class="line">09-28 22:22:47.850 1664 1943 I DisplayPowerController[0]: BrightnessEvent: disp=0, physDisp=local:0, brt=0.0, initBrt=0.0, rcmdBrt=NaN, preBrt=NaN, lux=0.0, preLux=0.0, hbmMax=1.0, hbmMode=off, rbcStrength=50, powerFactor=1.0, thrmMax=1.0, wasShortTermModelActive=false, flags=, reason=screen_off, autoBrightness=true</span><br><span class="line">09-28 22:22:47.851 917 917 I android.hardware.power-service-qti: Power setMode: 7 to: 0</span><br><span class="line">09-28 22:22:47.851 917 917 E QTI PowerHAL: Failed to acquire lock for hint_id: 1040.</span><br><span class="line">09-28 22:22:47.853 1664 1943 I PowerManagerService: Dozing...</span><br></pre></td></tr></tbody></table></figure><p>可能和 doze 模式打开相关</p><p>搜索如何关闭 doze 模式，参考https://forum.xda-developers.com/t/disable-doze.4407685/,以及 GPT 中询问 "怎样在 adb 中使用命令禁止 doze 模式"</p><figure class="highlight plaintext"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">adb shell dumpsys deviceidle disable # 使用该命令可以禁用doze模式</span><br><span class="line">adb shell dumpsys deviceidle enable # 使用该命令可以禁用doze模式</span><br><span class="line">adb shell dumpsys deviceidle whitelist +<package_name> # 在特定应用上禁用doze模式</span><br><span class="line">adb shell dumpsys deviceidle whitelist -<package_name> # 去掉特定应用禁用doze模式</span><br></pre></td></tr></tbody></table></figure><p>实测在 LinuxDeploy 中设置中打开 <code>Lock screen</code> 和 <code>Wake lock</code>,并<strong>接通电源</strong>使用，可以保持较为流畅的体验，"Kerneladiutor"并不能解决 CPU" 睡眠 " 问题</p><p><del>实际上打开</del><code>Lock screen</code><del>开关之后，并不会导致屏幕常亮，而且可以照常锁屏，不会导致睡眠问题</del></p><p><del>但是打开</del><code>Lock screen</code><del>开关后电量会掉的比较快，所以使用时打开该开关，待机时关闭该开关即可</del></p><p>(当然，也有可能是将 USB 默认配置改成了文件传输，才让它保持 CPU),按照上述设置，打开 Lock Screen 但是接手机充电器试试，出现睡眠问题</p><p>开发者选项中开启 "Stay awake", 之后关闭屏幕，还是卡顿</p><p>参考:https://stackoverflow.com/questions/7617459/how-to-keep-cpu-from-sleeping-when-screen-is-turned-off-in-android</p><p>参考: https://developer.android.com/training/scheduling/wakelock</p><p><del>可能是 LinuxDeploy 中的 CPU 锁没有生效</del></p><p>现象：实际使用的时候，已经在 LinuxDeploy 中打开了 <code>Wifi Lock</code> 和 <code>CPU Wake Lock</code>,但是有时候还是发现打开笔记会卡顿，刷新会卡 LOGO 界面，但是点亮屏幕就会非常快刷新页面，不存在卡顿</p><p>这很有可能是 CPU 调度策略引起的问题，<strong>锁屏</strong>后 CPU 进入了 "Deep Sleep" 状态</p><p>通过以下命令可以看到 CPU 核心的运行情况，但是当卡顿情况发生时，命令的输入都会变得卡顿</p><figure class="highlight bash"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">lscpu -e</span><br><span class="line"></span><br><span class="line"><span class="comment"># 如果提示命令不存在, 需要下载util-linux</span></span><br><span class="line">apt-get install util-linux</span><br></pre></td></tr></tbody></table></figure><p>注意: <strong>使用 Kerneladiutor 设置后还是无法避免锁屏后手机进入 "睡眠" 模式导致卡顿，以下内容可以选择性忽略</strong></p><p>通过 <code>Kernel adiutor</code> 可以调整 CPU 运行策略</p><p>下载地址:https://f-droid.org/en/packages/com.nhellfire.kerneladiutor</p><p>在 CPU 选项中，更改 CPU Govemor</p><p>以下内容引用自 ChatGPT</p><figure class="highlight plaintext"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br></pre></td><td class="code"><pre><span class="line">Performance（性能）：</span><br><span class="line">Performance模式将CPU设置为最高性能状态，以实现最佳的性能表现。这意味着CPU频率会尽可能地提高，以获得更高的计算能力。但是，这也会导致电池更快地耗尽，因此通常不适用于需要长时间使用电池的情况。</span><br><span class="line"></span><br><span class="line">Powersave（节能）：</span><br><span class="line">Powersave模式旨在最大程度地减少CPU功耗，从而延长电池寿命。它会将CPU频率降低到较低的水平，以降低性能，但可以显著减少电池的消耗。这适用于长时间不需要高性能的情况。</span><br><span class="line"></span><br><span class="line">Ondemand（按需）：</span><br><span class="line">Ondemand模式是一种动态调整CPU频率的模式，它根据系统负载自动调整CPU频率。当系统负载较低时，CPU频率会降低以节省电池电量，而在需要更多性能时，它会提高频率以提供更好的响应性能。</span><br><span class="line"></span><br><span class="line">Interactive（交互式）：</span><br><span class="line">Interactive模式是一种类似于Ondemand的动态调整模式，但更加灵活。它更快地响应负载变化，以提供更好的用户体验。这个模式在需要快速响应输入和任务切换的情况下非常有用。</span><br><span class="line"></span><br><span class="line">Conservative（保守）：</span><br><span class="line">Conservative模式也是一种动态调整模式，但相对于Ondemand和Interactive来说更加保守。它会慢慢地增加或降低CPU频率，以更平滑地适应负载变化。</span><br><span class="line"></span><br><span class="line">Userspace（用户空间）：</span><br><span class="line">Userspace模式允许用户手动设置CPU频率，而不是依赖于内核的自动调整。用户可以根据自己的需求来设置CPU频率，但需要小心，以避免不稳定或过度耗电。</span><br><span class="line"></span><br><span class="line">Performance Bias（性能偏好）：</span><br><span class="line">这是一种类似于Performance模式的模式，但稍微降低了CPU的性能以节省一些电量。它可以提供相对较高的性能，同时保持一定的电池寿命。</span><br></pre></td></tr></tbody></table></figure><p>可以考虑将小核设置为 Performance, 大核保持 Interactive 不变，看是否会减少卡顿 (貌似不行)</p><p>将大小核都设置为 Performance</p><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kity.min.js"></script><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kityminder.core.min.js"></script><script defer="true" type="text/javascript" src="https://unpkg.com/[email protected]/dist/mindmap.min.js"></script><link rel="stylesheet" type="text/css" href="https://unpkg.com/[email protected]/dist/mindmap.min.css">]]></content>
<summary type="html"><p>手头上的旧手机为小米 6, 本文可能部分内容只在小米 6 上适用 [xiaomi 6
sagit]</p>
<p>且本文主要讨论 LinuxDeploy (需要 root) 的方式，
非 root 用户可使用 Termux 方式</p></summary>
<category term="Linux" scheme="https://fetasty.github.io/categories/Linux/"/>
<category term="Linux" scheme="https://fetasty.github.io/tags/Linux/"/>
<category term="Android" scheme="https://fetasty.github.io/tags/Android/"/>
</entry>
<entry>
<title>健康生活清单</title>
<link href="https://fetasty.github.io/posts/1ef19147/"/>
<id>https://fetasty.github.io/posts/1ef19147/</id>
<published>2022-03-07T13:28:25.000Z</published>
<updated>2023-06-19T06:55:27.941Z</updated>
<content type="html"><![CDATA[<p>现在多少年轻人都莫名其妙的大病或猝死，不好的生活习惯会让我们的身体一直处于亚健康状态，后面可能任何一个小的触发点都能是压垮骆驼的最后一根稻草，比如生个气喝个酒甚至猛然的剧烈运动一下都可能直接人没了</p><span id="more"></span><p>一份简单的健康生活清单，说着简单，但坚持做下来不简单</p><ul><li>饮食<ul><li><span style="color: green">多喝水</span></li><li><span style="color: green">多吃蔬菜水果</span></li><li><span style="color: orange">少吃油炸烧烤腌制</span> (含致癌物)</li><li><span style="color: red"> 少吃游离糖，少吃零食，少喝奶茶</span>(高糖高热量，危害多到写不下)</li><li><span style="color: red"> 不饮酒，不喝含酒精饮料</span>(含酒精饮料为一级致癌物 (与黄曲霉素一个等级))</li></ul></li><li> 作息<ul><li><span style="color: green">早睡早起</span> (熬夜的危害实在太多了，都懒得写)</li><li><span style="color: green"> 保持午休</span> (30 分钟左右即可，双相睡眠对身体非常好)</li></ul></li><li> 活动<ul><li><span style="color: green">保持锻炼</span>(每周至少 3 次不少于 30 分钟的运动)</li><li><span style="color: red"> 不要长时间埋头，电脑垫高</span> (保护颈椎，出问题时才知道多严重)</li></ul></li></ul><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kity.min.js"></script><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kityminder.core.min.js"></script><script defer="true" type="text/javascript" src="https://unpkg.com/[email protected]/dist/mindmap.min.js"></script><link rel="stylesheet" type="text/css" href="https://unpkg.com/[email protected]/dist/mindmap.min.css">]]></content>
<summary type="html"><p>现在多少年轻人都莫名其妙的大病或猝死，
不好的生活习惯会让我们的身体一直处于亚健康状态，
后面可能任何一个小的触发点都能是压垮骆驼的最后一根稻草，
比如生个气喝个酒甚至猛然的剧烈运动一下都可能直接人没了</p></summary>
<category term="生活" scheme="https://fetasty.github.io/categories/life/"/>
</entry>
<entry>
<title>C++ 中 const 与 constexpr 的区别</title>
<link href="https://fetasty.github.io/posts/106f98c5/"/>
<id>https://fetasty.github.io/posts/106f98c5/</id>
<published>2022-03-07T13:25:57.000Z</published>
<updated>2023-06-19T08:50:35.370Z</updated>
<content type="html"><![CDATA[<p>原文地址: <a href="https://www.cnblogs.com/fortunely/p/14550145.html">const 和 constexpr 区别与联系</a></p><p>提到 const 和 constexpr, 就需要引入常量表达式。常量表达式是指值不会改变，并且编译过程就能得到计算结果的表达式. => 编译阶段就能得到值，并且不能改变.</p><span id="more"></span><p><strong>const 修饰对象无法修改，constexpr 更侧重于修饰对象编译期确定且无法修改. </strong>具体区别，体现在以下两个方面：</p><h2 id="修饰变量">修饰变量</h2><p><strong>const 变量，表示一个变量无法改变，但初值并不确定，不能在编译阶段决定. </strong></p><p>比如，</p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="type">const</span> <span class="type">int</span> sz = <span class="built_in">get_size</span>(); <span class="comment">// 虽然sz无法改变, 但get_size()</span></span><br></pre></td></tr></tbody></table></figure><p>编译阶段无法确定值，也就是说 sz 不是常量表达式</p><p><strong>constexpr 变量，编译器在编译阶段验证变量是否为一个常量表达式.</strong></p><p>constexpr 侧重变量初值编译阶段确定，且无法修改.如果认定变量是一个常量表达式，就把它声明称 constexpr 类型.</p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">constexpr</span> <span class="type">int</span> mf = <span class="number">20</span>; <span class="comment">// 字面量20是常量表达式</span></span><br><span class="line"><span class="keyword">constexpr</span> <span class="type">int</span> limit = mf + <span class="number">1</span>; <span class="comment">// mf + 1是常量表达式</span></span><br><span class="line"><span class="keyword">constexpr</span> <span class="type">int</span> sz = <span class="built_in">size</span>(); <span class="comment">// 只有当size是constexpr函数时, 才是正确的</span></span><br></pre></td></tr></tbody></table></figure><h2 id="修饰指针">修饰指针</h2><p>const 修饰指针分为两种情况：顶层 const, 底层 const.</p><p><strong>顶层 const 代表指针变量自身无法修改；底层 const 代表指针所指对象无法修改.</strong></p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="type">int</span> i = <span class="number">10</span>;</span><br><span class="line"><span class="type">int</span> *<span class="type">const</span> p1 = &i; <span class="comment">// 顶层const</span></span><br><span class="line"><span class="type">const</span> <span class="type">int</span> *p2 = &i; <span class="comment">// 底层const</span></span><br><span class="line"></span><br><span class="line">p1 = <span class="keyword">new</span> <span class="built_in">int</span>(<span class="number">20</span>); <span class="comment">// 错误, 顶层const指针自身无法修改</span></span><br><span class="line">p2 = <span class="keyword">new</span> <span class="built_in">int</span>(<span class="number">30</span>); <span class="comment">// 正确, 底层const指针可以修改</span></span><br><span class="line">*p1 = <span class="number">40</span>; <span class="comment">// 正确, 顶层const指针指向的对象可以修改</span></span><br><span class="line">*p2 = <span class="number">40</span>; <span class="comment">// 错误, 底层const指针指向的对象无法修改</span></span><br></pre></td></tr></tbody></table></figure><p>constexpr 修饰指针，仅对指针有效，与指针所指对象无关</p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// j的定义必须放在函数体外</span></span><br><span class="line"><span class="type">int</span> j = <span class="number">30</span>;</span><br><span class="line"></span><br><span class="line"><span class="comment">// 函数体内</span></span><br><span class="line"><span class="keyword">constexpr</span> <span class="type">int</span> *pp1 = &j; <span class="comment">// 等价于 int constexpr *pp1 = &j;</span></span><br><span class="line">cout << *pp1 << endl; <span class="comment">// 30</span></span><br><span class="line">*pp1 = <span class="number">40</span>;</span><br><span class="line">cout << j << endl; <span class="comment">// 40</span></span><br><span class="line">pp1 = <span class="literal">nullptr</span>; <span class="comment">// 错误, constexpr指针无法修改</span></span><br></pre></td></tr></tbody></table></figure><h2 id="修饰函数">修饰函数</h2><p>const 修饰成员函数，通常称为 const 函数，表示该函数不会修改类的状态（即不会通过任何方式修改类数据成员）. 另外，const 类对象，只能调用 const 函数，确保不会修改类的数据成员.</p><p>constexpr 无法修饰成员函数，只能作为函数返回值类型，表明该函数返回的是一个编译期可确定的常量；constexpr被隐式隐式指定为内联函数，只能在类的声明中定义（.h 文件）.</p><p>参见 <a href="https://blog.csdn.net/lihao21/article/details/8634876">C++ 的 const 类成员函数</a></p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// A.h</span></span><br><span class="line"><span class="keyword">class</span> <span class="title class_">A</span>{</span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line"> <span class="built_in">A</span>():<span class="built_in">curSize</span>(<span class="number">10</span>) {}</span><br><span class="line"> <span class="function"><span class="type">void</span> <span class="title">setSize</span><span class="params">(<span class="type">int</span> size)</span> </span>{ size++; }</span><br><span class="line"></span><br><span class="line"> <span class="comment">// const函数</span></span><br><span class="line"> <span class="function"><span class="type">int</span> <span class="title">size</span><span class="params">()</span> <span class="type">const</span> </span>{ <span class="keyword">return</span> curSize; } <span class="comment">// 正确示例：不写任何数据成员</span></span><br><span class="line"> <span class="function"><span class="type">int</span> <span class="title">size</span><span class="params">()</span> <span class="type">const</span> </span>{ curSize = <span class="number">2</span>; <span class="keyword">return</span> curSize; }; <span class="comment">// 错误示例： const函数不能修改任何类的数据成员</span></span><br><span class="line"> <span class="function"><span class="type">int</span> <span class="title">size</span><span class="params">()</span> <span class="type">const</span> </span>{ <span class="built_in">setSize</span>(); <span class="keyword">return</span> curSize; } <span class="comment">// 错误示例：const函数不能调用任何可能导致类的数据成员改变的函数, 也就是说, 如果调用自身成员函数, 只能调用const函数</span></span><br><span class="line"> <span class="function"><span class="type">const</span> <span class="type">int</span> <span class="title">size</span><span class="params">()</span> </span>{ <span class="keyword">return</span> curSize; } <span class="comment">// 函数返回值为const类型：函数体可以修改数据成员, 但返回类型是const, 也就是调用者无法修改</span></span><br><span class="line"></span><br><span class="line"> <span class="comment">// 函数返回值为constexpr类型</span></span><br><span class="line"> <span class="function"><span class="keyword">constexpr</span> <span class="type">int</span> <span class="title">getMaxSize</span><span class="params">()</span> </span>{ <span class="keyword">return</span> INT_MAX; } <span class="comment">// 正确示例：返回常量值</span></span><br><span class="line"> <span class="comment">// 错误示例：vec.size()运行时确定, 不能在编译期决定</span></span><br><span class="line"> <span class="function"><span class="keyword">constexpr</span> <span class="type">int</span> <span class="title">getMaxSize</span><span class="params">()</span></span></span><br><span class="line"><span class="function"> </span>{</span><br><span class="line"> std::vector<<span class="type">int</span>> vec;</span><br><span class="line"> vec.<span class="built_in">push_back</span>(<span class="number">1</span>);</span><br><span class="line"> vec.<span class="built_in">push_back</span>(<span class="number">2</span>);</span><br><span class="line"> <span class="keyword">return</span> vec.<span class="built_in">size</span>();</span><br><span class="line"> }</span><br><span class="line"> <span class="comment">// 正确：虽然看起来返回的是变量, 但编译器可确定</span></span><br><span class="line"> <span class="function"><span class="keyword">constexpr</span> <span class="type">int</span> <span class="title">getMaxSize</span><span class="params">(<span class="type">int</span> a, <span class="type">int</span> b)</span></span></span><br><span class="line"><span class="function"> </span>{</span><br><span class="line"> <span class="keyword">return</span> a + b;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"><span class="keyword">private</span>:</span><br><span class="line"> <span class="type">int</span> curSize;</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="comment">// A.cpp</span></span><br><span class="line"><span class="comment">// 错误示例：constexpr被隐式指定为内联函数, 只能在.h 类内定义, 不能在类实现文件(.cpp)中定义</span></span><br><span class="line"><span class="function"><span class="keyword">constexpr</span> <span class="type">int</span> <span class="title">A::getMaxsize</span><span class="params">()</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="keyword">return</span> <span class="number">1</span>;</span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kity.min.js"></script><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kityminder.core.min.js"></script><script defer="true" type="text/javascript" src="https://unpkg.com/[email protected]/dist/mindmap.min.js"></script><link rel="stylesheet" type="text/css" href="https://unpkg.com/[email protected]/dist/mindmap.min.css">]]></content>
<summary type="html"><p>原文地址: <a href="https://www.cnblogs.com/fortunely/p/14550145.html">const 和 constexpr 区别与联系</a></p>
<p>提到 const 和 constexpr, 就需要引入常量表达式。常量表达式是指值不会改变，
并且编译过程就能得到计算结果的表达式. =&gt; 编译阶段就能得到值，
并且不能改变.</p></summary>
<category term="C++" scheme="https://fetasty.github.io/categories/C/"/>
<category term="C++" scheme="https://fetasty.github.io/tags/C/"/>
</entry>
<entry>
<title>添加糖 - 甜蜜杀手</title>
<link href="https://fetasty.github.io/posts/90d1f41c/"/>
<id>https://fetasty.github.io/posts/90d1f41c/</id>
<published>2022-03-07T13:23:43.000Z</published>
<updated>2023-06-19T06:55:27.941Z</updated>
<content type="html"><![CDATA[<p>让人上瘾，又伤心、伤脑…… 这味调料家家都有，但劝你别多吃！</p><p>2022-03-01 14:00 来源： CCTV 回家吃饭</p><p> 糖果、冰激凌、蛋糕、饼干、巧克力…… 甜食让不少人欲罢不能，情绪不好时来一口，感觉整个世界都明媚了；时下的网红饮品奶茶，更是被戏称为 “肥宅快乐水”, 深受年轻人的喜爱～</p><p> 殊不知，大快朵颐的同时，甜食更像是一位隐形的 “甜蜜杀手”,不仅会让人慢慢 “上瘾”, 还会悄悄摧毁着你的身体！</p><span id="more"></span><h2 id="长期吃太多糖-从上到下毁全身">长期吃太多糖，从上到下毁全身</h2><p> 2012 年 2 月，发表在国际顶级学术刊物《Nature》杂志的一篇题为《公共卫生：糖的毒性真相》的文章指出：糖就像烟草和酒精一样，而且糖的危害远在脂肪和卡路里之上！</p><h3 id="糖-会诱发多种癌症">1 糖，会诱发多种癌症</h3><p> 长期高糖摄入会导致肥胖和胰岛素抵抗，造成内氧化应激、内分泌紊乱及免疫功能障碍，从而导致肿瘤的发生风险增加.</p><p> 2020 年刊发在《美国临床营养学杂志》的一项研究，对 10 万余人进行了长达 5.9 年的随访，通过饮食记录大家吃糖的情况.结果发现：</p><p> ①总糖摄入量与较高的总癌症风险相关，且这种联系主要来自乳腺癌；</p><p> ②添加糖、蔗糖、含糖饮料中的糖等与癌症风险的增加显著相关性.</p><p> 另外，瑞典科学家花 9 年时间对 8 万人进行了跟踪调查，结果显示，经常过量摄取甜食、果酱等高糖食物的人，患胰腺癌的风险要比其他人高出 70%~90%.</p><p> 而除了人人敬而远之的癌症，吃糖过多还会带来以下危害：</p><h3 id="形成龋齿">2 形成龋齿</h3><p> 摄入过多糖分食物，容易导致龋齿产生.因为在口腔中残留的糖分非常容易被细菌分解并发酵，从而产生酸性的物质，损坏牙釉质.</p><h3 id="加速皮肤老化">3 加速皮肤老化</h3><p> 摄入太多糖分时，不仅容易使皮肤松弛，滋生皱纹，肤色暗黄且没有光泽；也会使得酪氨酸酶异常活跃，加快黑色素沉淀速度，使得皮肤暗沉，容易长斑；甚至易堵塞毛孔而形成痤疮.</p><h3 id="伤大脑">4 伤大脑</h3><p> 吃太多糖，会伤害脑细胞，降低记忆力，简单来说就是吃糖过多会让人变笨.</p><h3 id="诱发心脏病">5 诱发心脏病</h3><p> 进食含糖量过高的食品会使血液中的甘油三酯升高，从而增加患心血管疾病的风险.</p><p> 另外，一项针对 11.8 万美国人的 34 年随访研究显示：每天饮用 2 次以上含糖饮料的人，死于心血管疾病的风险上升 31%.</p><h2 id="控糖-控的是添加糖">控糖，控的是 “添加糖”</h2><p> 糖类是人体必须的三大营养物质之一，应该均衡地摄入.<strong>真正需要限制摄入的是 “添加糖”（游离糖）</strong>：</p><p> ①添加在加工食品中的白糖、冰糖、红糖、黑糖.它们的主要成分都是蔗糖，加工原料均为甘蔗或甜菜，只是加工工艺不同.</p><p> ②各种添加了果葡糖浆、葡萄糖浆、麦芽糖浆、淀粉糖浆的含糖饮品.</p><p> ③水果汁和蜂蜜也属于要限制的糖类.水果榨汁过程中会损失大量膳食纤维，消化吸收会加快；蜂蜜主要是果糖和葡萄糖，属于应该控制的糖类.</p><p> 世界卫生组织建议要终生控制游离糖摄入，但是现实中又很难做到完全不吃。所以，我们最好将每天的游离糖摄入量控制在 25g 以内.</p><h3 id="代糖-也别吃过量">代糖，也别吃过量</h3><p> 现在不少商家会选择用糖醇或人工甜味剂替代添加糖，不牺牲风味的同时，实现限糖.</p><ol type="1"><li>糖醇</li></ol><p> 糖醇养型合成甜味剂，我们在配料表中看到的赤藓糖醇、山梨糖醇、麦芽糖醇、甘露醇、木糖醇等配料，就是糖醇家族的成员，优势也非常明显：</p><p> ①提供甜味的同时，提供的热量大多远低于蔗糖；</p><p> ②摄入后不会引起血糖大幅度升高；</p><p> ③在口腔中也不受微生物作用，不会引起龋齿.</p><ol start="2" type="1"><li>人工甜味剂</li></ol><p> 人工甜味剂属于非营养型甜味剂，我们在配料表中看到的糖精、安赛蜜、阿斯巴甜等配料就属于这个类别.</p><p> 和糖醇一样，人工甜味剂也能在一定程度上帮助人们降低热量和糖分的摄入，但是它绝不是放心之选 —— 其能起打开食欲的作用，在心理上反而会对那些又甜、又实际存在热量的食物产生更强烈的依赖，这样一来可能会间接促成食物和能量摄入超标的结局.</p><p> 总的来说，不管是糖醇还是人工甜味剂，日常可以以少量、低频次的节奏去摄入，但不能毫无节制的食用.</p><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kity.min.js"></script><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kityminder.core.min.js"></script><script defer="true" type="text/javascript" src="https://unpkg.com/[email protected]/dist/mindmap.min.js"></script><link rel="stylesheet" type="text/css" href="https://unpkg.com/[email protected]/dist/mindmap.min.css">]]></content>
<summary type="html"><p>让人上瘾，又伤心、伤脑…… 这味调料家家都有，但劝你别多吃！</p>
<p>2022-03-01 14:00 来源： CCTV 回家吃饭</p>
<p> 糖果、冰激凌、蛋糕、饼干、巧克力…… 甜食让不少人欲罢不能，
情绪不好时来一口，感觉整个世界都明媚了；时下的网红饮品奶茶，
更是被戏称为 “肥宅快乐水”, 深受年轻人的喜爱～</p>
<p> 殊不知，大快朵颐的同时，甜食更像是一位隐形的 “甜蜜杀手”,
不仅会让人慢慢 “上瘾”, 还会悄悄摧毁着你的身体！</p></summary>
<category term="生活" scheme="https://fetasty.github.io/categories/life/"/>
</entry>
<entry>
<title>dumpbin 查看 DLL 导出信息</title>
<link href="https://fetasty.github.io/posts/e6310a89/"/>
<id>https://fetasty.github.io/posts/e6310a89/</id>
<published>2022-02-22T13:17:40.000Z</published>
<updated>2023-06-19T08:48:51.670Z</updated>
<content type="html"><![CDATA[<p>dumpbin 是 vs 提供的一个工具，可以用于查看 dll/exe 的信息，32 位还是 64 位，导出函数等</p><span id="more"></span><p><a href="https://blog.csdn.net/luoyu510183/article/details/93666808">https://blog.csdn.net/luoyu510183/article/details/93666808</a></p><p>如果导入 dll 时发现没有找到该函数，要根据 dll 的导出约定方式设置对应的导入方式，否则虽然函数名一样但实际上符号是不同的.</p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">dumpbin /exports xxx.dll</span><br></pre></td></tr></tbody></table></figure><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">pragma</span> once</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">extern</span> <span class="string">"C"</span> {</span><br><span class="line"> <span class="comment">//extern "C" + _stdcall,函数导出符号为 _CreateNativeManager@0 : _+函数名+@+传参字节数</span></span><br><span class="line"> <span class="comment">//由于_stdcall是被调用方清理堆栈, 所以函数符号里面包含了传参的信息</span></span><br><span class="line"> _declspec(dllexport) <span class="function">NativeManager* _stdcall <span class="title">CreateNativeManager</span><span class="params">()</span></span>;</span><br><span class="line"> _declspec(dllexport) <span class="function"><span class="type">void</span> _stdcall <span class="title">ReleaseNativeManager</span><span class="params">()</span></span>;</span><br><span class="line"> _declspec(dllexport) <span class="built_in">void</span>(_stdcall ExSetLogHandler)(LogHandler handler);</span><br><span class="line"> <span class="comment">//extern "C" + _cdecl,函数导出符号为 ReleaseNativeManager2 : 函数名</span></span><br><span class="line"> <span class="comment">//由于_cdecl是调用方清理堆栈, 所以只需要函数名就可以</span></span><br><span class="line"> _declspec(dllexport) <span class="built_in">void</span>(_cdecl ReleaseNativeManager2)();</span><br><span class="line">}</span><br><span class="line"><span class="comment">//不使用extern的情况下, 是C++的导出方式, 函数符号如下：</span></span><br><span class="line"><span class="comment">//?ReleaseNativeManager1@@YGXH@Z : ?+函数名+@@YG+返回类型+参数1类型...+@Z</span></span><br><span class="line"><span class="comment">//如果是_cdecl @YG变为@YA</span></span><br><span class="line"><span class="comment">//如果没有参数即参数为void,则以Z结尾, 例如：</span></span><br><span class="line"><span class="comment">//?ReleaseNativeManager3@@YAXXZ : ?+函数名+@@YA+返回类型+XZ</span></span><br><span class="line"><span class="comment">//以上 X表示 void类型, H表示int参数类型</span></span><br><span class="line">_declspec(dllexport) <span class="built_in">void</span>(_stdcall ReleaseNativeManager1)(<span class="type">int</span> num);</span><br><span class="line">_declspec(dllexport) <span class="built_in">void</span>(_cdecl ReleaseNativeManager3)();</span><br></pre></td></tr></tbody></table></figure><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kity.min.js"></script><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kityminder.core.min.js"></script><script defer="true" type="text/javascript" src="https://unpkg.com/[email protected]/dist/mindmap.min.js"></script><link rel="stylesheet" type="text/css" href="https://unpkg.com/[email protected]/dist/mindmap.min.css">]]></content>
<summary type="html"><p>dumpbin 是 vs 提供的一个工具，可以用于查看 dll/exe 的信息，32 位还是 64 位，
导出函数等</p></summary>
<category term="C++" scheme="https://fetasty.github.io/categories/C/"/>
<category term="C++" scheme="https://fetasty.github.io/tags/C/"/>
<category term="DLL" scheme="https://fetasty.github.io/tags/DLL/"/>
</entry>
<entry>
<title>Python 中的可变对象与不可变对象</title>
<link href="https://fetasty.github.io/posts/c3f5fb77/"/>
<id>https://fetasty.github.io/posts/c3f5fb77/</id>
<published>2022-02-21T12:18:46.000Z</published>
<updated>2023-06-19T06:55:27.939Z</updated>
<content type="html"><![CDATA[<p>Python 中只存在 “引用传递” 这一种传递方式，准确来说应该是<strong>指针传递</strong> ,通过 <code>id()</code> 函数可以确定，参数传入前和传入后的地址值一样</p><p>所谓的对象可变与不可变，其实是看是否提供了修改自身对象的方法</p><span id="more"></span><p><strong>变量无类型，对象有类型</strong></p><p>不可变 (immutable) 对象类型 (指针地址不可变)</p><ul><li>int</li><li>float</li><li>decimal</li><li>complex</li><li>bool</li><li>str</li><li>tuple</li><li>range</li><li>frozenset</li><li>bytes</li></ul><p>可变 (mutable) 对象类型</p><ul><li>list</li><li>dict</li><li>set</li><li>bytearray</li></ul><p>user-defined classes (unless specifically made immutable)</p><p>Python 中的对象类型分为 <strong>可变类型</strong> 和<strong>不可变类型</strong></p><p>例如: Python 中的数字是不可变类型</p><figure class="highlight python"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line">a = <span class="number">2</span> <span class="comment"># 变量 a 指向一个 Number 对象</span></span><br><span class="line">b = <span class="number">2</span> <span class="comment"># 变量 b 和 a 指向同一个 Number 对象 此时 id(a) == id(b)</span></span><br><span class="line">a = <span class="number">1</span> <span class="comment"># 变量 a 指向一个新的 Number 对象, 而并不是 a 原本指向的 Number 对象发生了改变！ 此时 id(a) != id(b)</span></span><br><span class="line"></span><br><span class="line"><span class="comment"># 同样, 函数参数传递时也是如此</span></span><br><span class="line"><span class="keyword">def</span> <span class="title function_">add</span>(<span class="params">num</span>):</span><br><span class="line"> <span class="built_in">print</span>(<span class="built_in">id</span>(num)) <span class="comment"># 第一次打印的 id 是与外部的参数的 id 一致 (引用传递, 准确来说是指针传递)</span></span><br><span class="line"> num += <span class="number">2</span> <span class="comment"># 改变了 num 指向的对象, id(num) 发生了改变, 但不影响外部传入变量的地址</span></span><br><span class="line"> <span class="built_in">print</span>(<span class="built_in">id</span>(num))</span><br><span class="line"></span><br><span class="line">add(a) <span class="comment"># 传递变量 a 其实是“引用传递”, 也就是将 a 指向的内存地址传递了</span></span><br></pre></td></tr></tbody></table></figure><p>即使对于可变类型，其实也是<strong>指针传递</strong></p><figure class="highlight python"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">def</span> <span class="title function_">test</span>(<span class="params">lst</span>):</span><br><span class="line"> <span class="built_in">print</span>(<span class="built_in">id</span>(lst)) <span class="comment"># 2263872110464</span></span><br><span class="line"> lst = [<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>]</span><br><span class="line"> <span class="built_in">print</span>(<span class="built_in">id</span>(lst)) <span class="comment"># 2263872133184</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">if</span> __name__ == <span class="string">'__main__'</span>:</span><br><span class="line"> l = [<span class="number">9</span>, <span class="number">8</span>, <span class="number">7</span>]</span><br><span class="line"> <span class="built_in">print</span>(<span class="built_in">id</span>(l)) <span class="comment"># 2263872110464</span></span><br><span class="line"> <span class="built_in">print</span>(l) <span class="comment"># [9, 8, 7]</span></span><br><span class="line"> test(l) <span class="comment"># 函数中改变的</span></span><br><span class="line"> <span class="built_in">print</span>(<span class="built_in">id</span>(l)) <span class="comment"># 2263872110464</span></span><br><span class="line"> <span class="built_in">print</span>(l) <span class="comment"># [9, 8, 7]</span></span><br><span class="line"></span><br></pre></td></tr></tbody></table></figure><p>可变类型的 "可变", 体现在下面这种情况</p><figure class="highlight python"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">def</span> <span class="title function_">test</span>(<span class="params">lst</span>):</span><br><span class="line"> <span class="built_in">print</span>(<span class="built_in">id</span>(lst)) <span class="comment"># 2389391376256</span></span><br><span class="line"> lst.append(<span class="number">33</span>)</span><br><span class="line"> <span class="built_in">print</span>(<span class="built_in">id</span>(lst)) <span class="comment"># 2389391376256</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">if</span> __name__ == <span class="string">"__main__"</span>:</span><br><span class="line"> l = [<span class="number">9</span>, <span class="number">8</span>, <span class="number">7</span>]</span><br><span class="line"> <span class="built_in">print</span>(<span class="built_in">id</span>(l)) <span class="comment"># 2389391376256</span></span><br><span class="line"> <span class="built_in">print</span>(l) <span class="comment"># [9, 8, 7]</span></span><br><span class="line"> test(l)</span><br><span class="line"> <span class="built_in">print</span>(<span class="built_in">id</span>(l)) <span class="comment"># 2389391376256</span></span><br><span class="line"> <span class="built_in">print</span>(l) <span class="comment"># [9, 8, 7, 33]</span></span><br><span class="line"></span><br></pre></td></tr></tbody></table></figure><p>参考文章:</p><p><a href="https://www.cnblogs.com/shiyublog/p/10809953.html">https://www.cnblogs.com/shiyublog/p/10809953.html</a></p><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kity.min.js"></script><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kityminder.core.min.js"></script><script defer="true" type="text/javascript" src="https://unpkg.com/[email protected]/dist/mindmap.min.js"></script><link rel="stylesheet" type="text/css" href="https://unpkg.com/[email protected]/dist/mindmap.min.css">]]></content>
<summary type="html"><p>Python 中只存在 “引用传递” 这一种传递方式，
准确来说应该是<strong>指针传递</strong> ,
通过 <code>id()</code> 函数可以确定，参数传入前和传入后的地址值一样</p>
<p>所谓的对象可变与不可变，其实是看是否提供了修改自身对象的方法</p></summary>
<category term="Python" scheme="https://fetasty.github.io/categories/Python/"/>
<category term="Python" scheme="https://fetasty.github.io/tags/Python/"/>
</entry>
<entry>
<title>Python 临时改变 Path 搜索目录</title>
<link href="https://fetasty.github.io/posts/285687f/"/>
<id>https://fetasty.github.io/posts/285687f/</id>
<published>2022-02-21T12:17:24.000Z</published>
<updated>2023-06-19T06:55:27.939Z</updated>
<content type="html"><![CDATA[<figure class="highlight python"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> sys</span><br><span class="line">sys.path.append(<span class="string">r".\lib"</span>)</span><br><span class="line"><span class="keyword">import</span> mymodule <span class="comment"># lib目录下的自定义模块</span></span><br></pre></td></tr></tbody></table></figure><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kity.min.js"></script><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kityminder.core.min.js"></script><script defer="true" type="text/javascript" src="https://unpkg.com/[email protected]/dist/mindmap.min.js"></script><link rel="stylesheet" type="text/css" href="https://unpkg.com/[email protected]/dist/mindmap.min.css">]]></content>
<summary type="html"><figure class="highlight python"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><sp</summary>
<category term="Python" scheme="https://fetasty.github.io/categories/Python/"/>
</entry>
<entry>
<title>Python 处理 C 语言结构</title>
<link href="https://fetasty.github.io/posts/669ef2f3/"/>
<id>https://fetasty.github.io/posts/669ef2f3/</id>
<published>2022-02-21T12:15:43.000Z</published>
<updated>2023-06-19T06:55:27.940Z</updated>
<content type="html"><![CDATA[<p>Python 可以高效率开发，但涉及到运算密集部分，还是应该交给 C/C++,这里就涉及到数据交互的结构与格式问题</p><span id="more"></span><p>//todo 不够详细，例子不具体，内存布局与解析没讲明白</p><figure class="highlight python"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> struct</span><br><span class="line"><span class="keyword">from</span> ctypes <span class="keyword">import</span> *</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="keyword">class</span> <span class="title class_">MyStruct</span>(<span class="title class_ inherited__">Structure</span>):</span><br><span class="line"> _fields_ = [</span><br><span class="line"> (<span class="string">"v1"</span>, c_char), <span class="comment"># c_byte</span></span><br><span class="line"> (<span class="string">"v2"</span>, c_char), <span class="comment"># c_byte</span></span><br><span class="line"> (<span class="string">"v1_dire"</span>, c_char), <span class="comment"># c_byte</span></span><br><span class="line"> (<span class="string">"v2_dire"</span>, c_char) <span class="comment"># c_byte</span></span><br><span class="line"> ]</span><br><span class="line"></span><br><span class="line"></span><br><span class="line">mys = MyStruct()</span><br><span class="line">mys.v1 = <span class="number">20</span></span><br><span class="line"><span class="built_in">print</span>(<span class="built_in">type</span>(mys.v1))</span><br><span class="line">mys.v2 = <span class="number">30</span></span><br><span class="line">mys.v1_dire = <span class="number">0</span></span><br><span class="line">mys.v2_dire = <span class="number">0</span></span><br><span class="line">msg = struct.pack(<span class="string">'cccc'</span>, mys.v1, mys.v2, mys.v1_dire, mys.v2_dire) <span class="comment"># BBBB</span></span><br><span class="line"><span class="built_in">print</span>(msg)</span><br><span class="line">ss = struct.unpack(<span class="string">'cccc'</span>, msg) <span class="comment"># BBBB</span></span><br></pre></td></tr></tbody></table></figure><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kity.min.js"></script><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kityminder.core.min.js"></script><script defer="true" type="text/javascript" src="https://unpkg.com/[email protected]/dist/mindmap.min.js"></script><link rel="stylesheet" type="text/css" href="https://unpkg.com/[email protected]/dist/mindmap.min.css">]]></content>
<summary type="html"><p>Python 可以高效率开发，但涉及到运算密集部分，还是应该交给 C/C++,
这里就涉及到数据交互的结构与格式问题</p></summary>
<category term="Python" scheme="https://fetasty.github.io/categories/Python/"/>
</entry>
<entry>
<title>C++ 中 new-delete 与 malloc-free 的比较</title>
<link href="https://fetasty.github.io/posts/f8def853/"/>
<id>https://fetasty.github.io/posts/f8def853/</id>
<published>2022-02-20T14:36:32.000Z</published>
<updated>2023-06-19T08:50:26.788Z</updated>
<content type="html"><![CDATA[<p>new-delete 与 malloc-free</p><span id="more"></span><h2 id="newdelete-与-mallocfree-的比较">new&delete 与malloc&free 的比较</h2><ul><li><code>malloc/free</code> 是 C 语言的库函数</li><li><code>new/delete</code> <code>new[]/delete[]</code> 是 C++中的运算符</li><li><code>malloc/free</code> 只是申请内存空间，释放空间</li><li><code>new/delete</code> 不仅会申请内存空间，还会根据类型初始化内存空间，this 指针绑定，调用构造函数和析构函数进行初始化或者清理等操作</li></ul><p>这里有两张网上找到的图</p><ol type="1"><li><p><code>new/delete</code> 实现 <img data-src="/posts/f8def853/new_delete%E5%AE%9E%E7%8E%B0.png" class=""></p></li><li><p><code>new[]/delete[]</code> 实现</p><img data-src="/posts/f8def853/new_delete%E6%95%B0%E7%BB%84%E5%AE%9E%E7%8E%B0.png" class=""></li></ol><p>不一定完全正确，但具有一定参考意义，<code>new[]</code> 文中说会多申请4 字节 空间，在开始位置存储对象个数，这里我在 64 位 编译环境下验证了一下，是前 8 字节 空间中存储的，应该与系统位数有关</p><p>测试环境: Win10 64 bit & GCC 8.1.0 64 bit</p><p>这里定义一个 Test 类作测试</p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">class</span> <span class="title class_">Test</span></span><br><span class="line">{</span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line"> <span class="type">static</span> <span class="type">int</span> index;</span><br><span class="line"> <span class="built_in">Test</span>()</span><br><span class="line"> {</span><br><span class="line"> x = ++index;</span><br><span class="line"> str = str + std::<span class="built_in">to_string</span>(x);</span><br><span class="line"> std::cout << <span class="string">"Test Constructor() this="</span> << <span class="keyword">this</span> << std::endl;</span><br><span class="line"> }</span><br><span class="line"> ~<span class="built_in">Test</span>()</span><br><span class="line"> {</span><br><span class="line"> std::cout << <span class="string">"Test Destructor() this="</span> << <span class="keyword">this</span> << std::endl;</span><br><span class="line"> }</span><br><span class="line"> <span class="function"><span class="type">void</span> <span class="title">Show</span><span class="params">()</span></span></span><br><span class="line"><span class="function"> </span>{</span><br><span class="line"> std::cout << <span class="string">"Test show x("</span> << x << <span class="string">"), str("</span> << str << <span class="string">")"</span> << std::endl;</span><br><span class="line"> }</span><br><span class="line"><span class="keyword">private</span>:</span><br><span class="line"> <span class="type">int</span> x;</span><br><span class="line"> std::string str {<span class="string">"sssaaa"</span>};</span><br><span class="line">};</span><br><span class="line"></span><br><span class="line"><span class="type">int</span> Test::index = <span class="number">0</span>;</span><br></pre></td></tr></tbody></table></figure><p>测试:</p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="type">int</span> <span class="title">main</span><span class="params">(<span class="type">int</span>, <span class="type">char</span>**)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="type">int</span> size = <span class="built_in">sizeof</span>(Test);</span><br><span class="line"> Test* p = <span class="keyword">new</span> Test[<span class="number">3</span>]();</span><br><span class="line"> <span class="type">uint64_t</span>* sp = (<span class="type">uint64_t</span>*)p - <span class="number">1</span>;</span><br><span class="line"> std::cout << <span class="string">"Test obj size: "</span> << *sp << std::endl;</span><br><span class="line"> <span class="keyword">delete</span>[] p;</span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure><p>输出如下</p><figure class="highlight plaintext"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">Test Constructor() this=0x1d1e88</span><br><span class="line">Test Constructor() this=0x1d1eb0</span><br><span class="line">Test Constructor() this=0x1d1ed8</span><br><span class="line">Test obj size: 3</span><br><span class="line">Test Destructor() this=0x1d1ed8</span><br><span class="line">Test Destructor() this=0x1d1eb0</span><br><span class="line">Test Destructor() this=0x1d1e88</span><br></pre></td></tr></tbody></table></figure><p>如果我们修改一下上面的测试代码，更改一下前面的对象个数</p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="type">int</span> <span class="title">main</span><span class="params">(<span class="type">int</span>, <span class="type">char</span>**)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="type">int</span> size = <span class="built_in">sizeof</span>(Test);</span><br><span class="line"> Test* p = <span class="keyword">new</span> Test[<span class="number">3</span>]();</span><br><span class="line"> <span class="type">uint64_t</span>* sp = (<span class="type">uint64_t</span>*)p - <span class="number">1</span>;</span><br><span class="line"> std::cout << <span class="string">"Test obj size: "</span> << *sp << std::endl;</span><br><span class="line"> *sp = <span class="number">2</span>;</span><br><span class="line"> <span class="keyword">delete</span>[] p;</span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure><p>运行结果如下</p><figure class="highlight plaintext"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">Test Constructor() this=0x6e1e88</span><br><span class="line">Test Constructor() this=0x6e1eb0</span><br><span class="line">Test Constructor() this=0x6e1ed8</span><br><span class="line">Test obj size: 3</span><br><span class="line">Test Destructor() this=0x6e1eb0</span><br><span class="line">Test Destructor() this=0x6e1e88</span><br></pre></td></tr></tbody></table></figure><p><code>delete[]</code> 只执行了两次析构</p><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kity.min.js"></script><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kityminder.core.min.js"></script><script defer="true" type="text/javascript" src="https://unpkg.com/[email protected]/dist/mindmap.min.js"></script><link rel="stylesheet" type="text/css" href="https://unpkg.com/[email protected]/dist/mindmap.min.css">]]></content>
<summary type="html"><p>new-delete 与 malloc-free</p></summary>
<category term="C++" scheme="https://fetasty.github.io/categories/C/"/>
<category term="C++" scheme="https://fetasty.github.io/tags/C/"/>
</entry>
<entry>
<title>C++ 中使用 fstream 一次读取整个文件内容</title>
<link href="https://fetasty.github.io/posts/3579021f/"/>
<id>https://fetasty.github.io/posts/3579021f/</id>
<published>2022-02-20T14:33:41.000Z</published>
<updated>2023-06-19T08:50:23.272Z</updated>
<content type="html"><![CDATA[<p>原文地址 <a href="https://www.cnblogs.com/kex1n/p/4028428.html">https://www.cnblogs.com/kex1n/p/4028428.html</a></p><span id="more"></span><h2 id="读取到-char">读取到 char*</h2><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">std::ifstream t; <span class="type">int</span> length; t.<span class="built_in">open</span>(<span class="string">"file.txt"</span>); <span class="comment">// open input file</span></span><br><span class="line">t.<span class="built_in">seekg</span>(<span class="number">0</span>, std::ios::end); <span class="comment">// go to the end</span></span><br><span class="line">length = t.<span class="built_in">tellg</span>(); <span class="comment">// report location (this is the length)</span></span><br><span class="line">t.<span class="built_in">seekg</span>(<span class="number">0</span>, std::ios::beg); <span class="comment">// go back to the beginning</span></span><br><span class="line">buffer = <span class="keyword">new</span> <span class="type">char</span>[length]; <span class="comment">// allocate memory for a buffer of appropriate dimension</span></span><br><span class="line">t.<span class="built_in">read</span>(buffer, length); <span class="comment">// read the whole file into the buffer</span></span><br><span class="line">t.<span class="built_in">close</span>(); <span class="comment">// close file handle</span></span><br><span class="line"><span class="comment">// ... do stuff with buffer here ...</span></span><br></pre></td></tr></tbody></table></figure><h2 id="读取到-stdstring">读取到 std::string</h2><p>方法一</p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string"><string></span></span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string"><fstream></span></span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string"><streambuf></span></span></span><br><span class="line"><span class="function">std::ifstream <span class="title">t</span><span class="params">(<span class="string">"file.txt"</span>)</span></span>;</span><br><span class="line"><span class="function">std::string <span class="title">str</span><span class="params">((std::istreambuf_iterator<<span class="type">char</span>>(t)), std::istreambuf_iterator<<span class="type">char</span>>())</span></span>;</span><br></pre></td></tr></tbody></table></figure><p>方法二</p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string"><string></span></span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string"><fstream></span></span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string"><sstream></span></span></span><br><span class="line"><span class="function">std::ifstream <span class="title">t</span><span class="params">(<span class="string">"file.txt"</span>)</span></span>;</span><br><span class="line">std::stringstream buffer;</span><br><span class="line">buffer << t.<span class="built_in">rdbuf</span>();</span><br><span class="line"><span class="function">std::string <span class="title">contents</span><span class="params">(buffer.str())</span></span>;</span><br></pre></td></tr></tbody></table></figure><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kity.min.js"></script><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kityminder.core.min.js"></script><script defer="true" type="text/javascript" src="https://unpkg.com/[email protected]/dist/mindmap.min.js"></script><link rel="stylesheet" type="text/css" href="https://unpkg.com/[email protected]/dist/mindmap.min.css">]]></content>
<summary type="html"><p>原文地址 <a href="https://www.cnblogs.com/kex1n/p/4028428.html">https://www.cnblogs.com/kex1n/p/4028428.html</a></p></summary>
<category term="C++" scheme="https://fetasty.github.io/categories/C/"/>
<category term="C++" scheme="https://fetasty.github.io/tags/C/"/>
</entry>
<entry>
<title>C++ 中 lambda 使用注意事项</title>
<link href="https://fetasty.github.io/posts/24017eff/"/>
<id>https://fetasty.github.io/posts/24017eff/</id>
<published>2022-02-20T14:32:43.000Z</published>
<updated>2023-06-19T08:50:31.164Z</updated>
<content type="html"><![CDATA[<p><a href="https://blog.csdn.net/czyt1988/article/details/80149695">https://blog.csdn.net/czyt1988/article/details/80149695</a></p><ul><li><strong> 不要使用 lambda 以引用方式捕获局部变量</strong>！！！(悬挂引用)</li><li>lambda 捕获 this 时也需要注意，lambda 的调用时机是否在 this 的生命周期之外(类生命周期)</li></ul><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kity.min.js"></script><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kityminder.core.min.js"></script><script defer="true" type="text/javascript" src="https://unpkg.com/[email protected]/dist/mindmap.min.js"></script><link rel="stylesheet" type="text/css" href="https://unpkg.com/[email protected]/dist/mindmap.min.css">]]></content>
<summary type="html"><p><a href="https://blog.csdn.net/czyt1988/article/details/80149695">https://blog.csdn.net/czyt1988/article/details/80149695</a></p>
<ul>
<l</summary>
<category term="C++" scheme="https://fetasty.github.io/categories/C/"/>
<category term="C++" scheme="https://fetasty.github.io/tags/C/"/>
</entry>
<entry>
<title>C++ 中的 move 和 forward</title>
<link href="https://fetasty.github.io/posts/be74f994/"/>
<id>https://fetasty.github.io/posts/be74f994/</id>
<published>2022-02-20T14:31:12.000Z</published>
<updated>2023-06-19T08:50:11.139Z</updated>
<content type="html"><![CDATA[<p>std::move 和 std::forward 仅仅是进行类型转换的函数（实际上是函数模板）.std::move 无条件的将其参数转换为右值，而 std::forward 只在必要情况下进行这个转换，就是这样.</p><span id="more"></span><ol type="1"><li>std::move 执行一个无条件的转化到右值。它本身并不移动任何东西；</li><li>std::forward 把其参数转换为右值，仅仅在那个参数被绑定到一个右值时；</li><li>std::move 和 std::forward 在运行时（runtime）都不做任何事.</li></ol><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kity.min.js"></script><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kityminder.core.min.js"></script><script defer="true" type="text/javascript" src="https://unpkg.com/[email protected]/dist/mindmap.min.js"></script><link rel="stylesheet" type="text/css" href="https://unpkg.com/[email protected]/dist/mindmap.min.css">]]></content>
<summary type="html"><p>std::move 和 std::forward 仅仅是进行类型转换的函数（实际上是函数模板）.
std::move 无条件的将其参数转换为右值，
而 std::forward 只在必要情况下进行这个转换，就是这样.</p></summary>
<category term="C++" scheme="https://fetasty.github.io/categories/C/"/>
<category term="C++" scheme="https://fetasty.github.io/tags/C/"/>
</entry>
<entry>
<title>C++ 数组长度可以为变量吗</title>
<link href="https://fetasty.github.io/posts/7a9ccc43/"/>
<id>https://fetasty.github.io/posts/7a9ccc43/</id>
<published>2022-02-20T14:28:39.000Z</published>
<updated>2023-06-19T08:51:09.763Z</updated>
<content type="html"><![CDATA[<p>转载：原创程序喵大人 程序喵大人 (微信公众号) (收录于话题:C++ 精进之路)</p><p>推荐一下这个专题，讲 C++ 很棒</p><span id="more"></span><h2 id="c数组长度可以为变量吗">C++ 数组长度可以为变量吗？</h2><p>37 个</p><p>大家好，我是喵大人，今天跟大家分享的是关于 C++ 数组提出几点问题：</p><h3 id="预备">预备</h3><p>先看下这两段代码，并思考如下问题.</p><p>1、变量作为数组的长度可行吗？</p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string"><iostream></span></span></span><br><span class="line"><span class="keyword">using</span> <span class="keyword">namespace</span> std;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="type">void</span> <span class="title">func</span><span class="params">(<span class="type">int</span> num)</span> </span>{</span><br><span class="line"> <span class="type">int</span> array[num]; <span class="comment">// num > 0</span></span><br><span class="line"> cout << <span class="string">"num "</span> << num << endl;</span><br><span class="line"> cout << <span class="string">"sizeof array "</span> << <span class="built_in">sizeof</span>(array) << endl;</span><br><span class="line"> array[<span class="number">0</span>] = <span class="number">20</span>;</span><br><span class="line"> cout << <span class="string">"array[0] "</span> << array[<span class="number">0</span>] << endl;</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="type">int</span> <span class="title">main</span><span class="params">()</span> </span>{</span><br><span class="line"> <span class="built_in">func</span>(<span class="number">6</span>);</span><br><span class="line"> <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure><p>输出：</p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">num <span class="number">6</span></span><br><span class="line"><span class="keyword">sizeof</span> array <span class="number">24</span></span><br><span class="line">array[<span class="number">0</span>] <span class="number">20</span></span><br></pre></td></tr></tbody></table></figure><p>2、访问超过长度的数组下标的值会发生什么？</p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string"><iostream></span></span></span><br><span class="line"><span class="keyword">using</span> <span class="keyword">namespace</span> std;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="type">void</span> <span class="title">func</span><span class="params">()</span> </span>{</span><br><span class="line"> <span class="type">int</span> array[<span class="number">10</span>];</span><br><span class="line"> array[<span class="number">3</span>] = <span class="number">1</span>;</span><br><span class="line"> array[<span class="number">20</span>] = <span class="number">3</span>;</span><br><span class="line"> cout << <span class="string">"sizeof array "</span> << <span class="built_in">sizeof</span>(array) << endl;</span><br><span class="line"> cout << <span class="string">"array[3] "</span> << array[<span class="number">3</span>] << endl;</span><br><span class="line"> cout << <span class="string">"array[20] "</span> << array[<span class="number">20</span>] << endl;</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="type">int</span> <span class="title">main</span><span class="params">()</span> </span>{</span><br><span class="line"> <span class="built_in">func</span>();</span><br><span class="line"> <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure><p>输出：</p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">sizeof</span> array <span class="number">40</span></span><br><span class="line">array[<span class="number">3</span>] <span class="number">1</span></span><br><span class="line">array[<span class="number">20</span>] <span class="number">3</span></span><br></pre></td></tr></tbody></table></figure><h3 id="分析">分析</h3><p><strong>首先分析问题 1</strong>,我们平时看书学习过程中总看见说 C++ 的数组长度一定要是常量且不能是变量，很多资料需要在编译期确定栈帧的大小，如果是变量就不能在编译器确定栈帧大小，但上述代码为什么可以正常运行呢？光看不如实践，先看这样一段代码：</p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string"><iostream></span></span></span><br><span class="line"><span class="keyword">using</span> <span class="keyword">namespace</span> std;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="type">void</span> <span class="title">func2</span><span class="params">()</span> </span>{</span><br><span class="line"> <span class="type">int</span> a;</span><br><span class="line"> <span class="type">int</span> b[<span class="number">4</span>];</span><br><span class="line"> <span class="type">int</span> c;</span><br><span class="line"> cout << <span class="string">"func2a address "</span> << &a << endl;</span><br><span class="line"> cout << <span class="string">"func2b address "</span> << &b << endl;</span><br><span class="line"> cout << <span class="string">"func2c address "</span> << &c << endl;</span><br><span class="line"> <span class="comment">// func1();</span></span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="type">void</span> <span class="title">func3</span><span class="params">(<span class="type">int</span> num)</span> </span>{</span><br><span class="line"> <span class="type">int</span> a;</span><br><span class="line"> <span class="type">int</span> b[<span class="number">4</span>];</span><br><span class="line"> <span class="type">int</span> c;</span><br><span class="line"> cout << <span class="string">"func3a address "</span> << &a << endl;</span><br><span class="line"> cout << <span class="string">"func3b address "</span> << &b << endl;</span><br><span class="line"> cout << <span class="string">"func3c address "</span> << &c << endl;</span><br><span class="line"> <span class="built_in">func2</span>();</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="type">void</span> <span class="title">func4</span><span class="params">(<span class="type">int</span> num)</span> </span>{</span><br><span class="line"> <span class="type">int</span> a;</span><br><span class="line"> <span class="type">int</span> b[<span class="number">4</span>];</span><br><span class="line"> <span class="type">int</span> c;</span><br><span class="line"> cout << <span class="string">"func4a address "</span> << &a << endl;</span><br><span class="line"> cout << <span class="string">"func4b address "</span> << &b << endl;</span><br><span class="line"> cout << <span class="string">"func4c address "</span> << &c << endl;</span><br><span class="line"> <span class="built_in">func3</span>(num);</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="type">int</span> <span class="title">main</span><span class="params">()</span> </span>{</span><br><span class="line"> <span class="built_in">func4</span>(<span class="number">5</span>);</span><br><span class="line"> <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure><p>输出：</p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line">func4a address <span class="number">0x7ffeb675f418</span></span><br><span class="line">func4b address <span class="number">0x7ffeb675f420</span></span><br><span class="line">func4c address <span class="number">0x7ffeb675f41c</span></span><br><span class="line">func3a address <span class="number">0x7ffeb675f3c8</span></span><br><span class="line">func3b address <span class="number">0x7ffeb675f3d0</span></span><br><span class="line">func3c address <span class="number">0x7ffeb675f3cc</span></span><br><span class="line">func2a address <span class="number">0x7ffeb675f378</span></span><br><span class="line">func2b address <span class="number">0x7ffeb675f380</span></span><br><span class="line">func2c address <span class="number">0x7ffeb675f37c</span></span><br></pre></td></tr></tbody></table></figure><p>再看这段代码：</p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="type">void</span> <span class="title">func2</span><span class="params">()</span> </span>{</span><br><span class="line"> <span class="type">int</span> a;</span><br><span class="line"> <span class="type">int</span> b[<span class="number">4</span>];</span><br><span class="line"> <span class="type">int</span> c;</span><br><span class="line"> cout << <span class="string">"func2a address "</span> << &a << endl;</span><br><span class="line"> cout << <span class="string">"func2b address "</span> << &b << endl;</span><br><span class="line"> cout << <span class="string">"func2c address "</span> << &c << endl;</span><br><span class="line"> <span class="comment">// func1();</span></span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="type">void</span> <span class="title">func3</span><span class="params">(<span class="type">int</span> num)</span> </span>{</span><br><span class="line"> <span class="type">int</span> a;</span><br><span class="line"> <span class="type">int</span> b[num];</span><br><span class="line"> <span class="type">int</span> c;</span><br><span class="line"> cout << <span class="string">"func3a address "</span> << &a << endl;</span><br><span class="line"> cout << <span class="string">"func3b address "</span> << &b << endl;</span><br><span class="line"> cout << <span class="string">"func3c address "</span> << &c << endl;</span><br><span class="line"> <span class="built_in">func2</span>();</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="type">void</span> <span class="title">func4</span><span class="params">(<span class="type">int</span> num)</span> </span>{</span><br><span class="line"> <span class="type">int</span> a;</span><br><span class="line"> <span class="type">int</span> b[<span class="number">4</span>];</span><br><span class="line"> <span class="type">int</span> c;</span><br><span class="line"> cout << <span class="string">"func4a address "</span> << &a << endl;</span><br><span class="line"> cout << <span class="string">"func4b address "</span> << &b << endl;</span><br><span class="line"> cout << <span class="string">"func4c address "</span> << &c << endl;</span><br><span class="line"> <span class="built_in">func3</span>(num);</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="type">int</span> <span class="title">main</span><span class="params">()</span> </span>{</span><br><span class="line"> <span class="built_in">func4</span>(<span class="number">100</span>);</span><br><span class="line"> <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure><p>输出：</p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line">func4a address <span class="number">0x7ffff2c76568</span></span><br><span class="line">func4b address <span class="number">0x7ffff2c76570</span></span><br><span class="line">func4c address <span class="number">0x7ffff2c7656c</span></span><br><span class="line">func3a address <span class="number">0x7ffff2c76510</span></span><br><span class="line">func3b address <span class="number">0x7ffff2c76360</span></span><br><span class="line">func3c address <span class="number">0x7ffff2c76514</span></span><br><span class="line">func2a address <span class="number">0x7ffff2c76328</span></span><br><span class="line">func2b address <span class="number">0x7ffff2c76330</span></span><br><span class="line">func2c address <span class="number">0x7ffff2c7632c</span></span><br></pre></td></tr></tbody></table></figure><p>func4a - func3a = 88</p><p>func3a - func2a = 488</p><p>从上面两段代码其实可以看出 C++ 是支持变量长度的数组的，说不支持的那是很古老的编译器，在如下链接中也可以找到答案.</p><p><a href="https://c-for-dummies.com/blog/?p=3488">https://c-for-dummies.com/blog/?p=3488</a></p><p><a href="https://www.drdobbs.com/the-new-cwhy-variable-length-arrays/184401444">https://www.drdobbs.com/the-new-cwhy-variable-length-arrays/184401444</a></p><p><a href="https://stackoverflow.com/questions/1887097/why-arent-variable-length-arrays-part-of-the-c-standard">https://stackoverflow.com/questions/1887097/why-arent-variable-length-arrays-part-of-the-c-standard</a></p><p>备注：尽管 C++ 目前支持变量长度的数组，但是不建议使用，因为数组使用的是栈内存，栈内存是有大小限制的，一般是 8192 字节，既然长度是变量，那就可能是任何值，就有可能超过 8192, 这样就会 stackoverflow, 所以动态内存最好使用堆内存.</p><p><strong>再分析问题 2：操作超过数组长度的内存会发生什么？</strong></p><p>看下面这段代码：</p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string"><iostream></span></span></span><br><span class="line"><span class="keyword">using</span> <span class="keyword">namespace</span> std;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="type">void</span> <span class="title">func</span><span class="params">()</span> </span>{</span><br><span class="line"> <span class="type">int</span> array[<span class="number">10</span>];</span><br><span class="line"> array[<span class="number">3</span>] = <span class="number">1</span>;</span><br><span class="line"> array[<span class="number">40</span>] = <span class="number">3</span>;</span><br><span class="line"> cout << <span class="string">"sizeof array "</span> << <span class="built_in">sizeof</span>(array) << endl;</span><br><span class="line"> cout << <span class="string">"array[3] "</span> << array[<span class="number">3</span>] << endl;</span><br><span class="line"> cout << <span class="string">"array[40] "</span> << array[<span class="number">40</span>] << endl;</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="type">int</span> <span class="title">main</span><span class="params">()</span> </span>{</span><br><span class="line"> <span class="type">int</span> a[<span class="number">200</span>];</span><br><span class="line"> <span class="keyword">for</span> (<span class="type">int</span> i = <span class="number">0</span>; i < <span class="number">200</span>; ++i) {</span><br><span class="line"> a[i] = <span class="number">100</span>;</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">for</span> (<span class="type">int</span> i = <span class="number">0</span>; i < <span class="number">200</span>; ++i) {</span><br><span class="line"> cout << a[i] << <span class="string">" "</span>;</span><br><span class="line"> }</span><br><span class="line"> cout << endl << <span class="string">"====================="</span> << endl;</span><br><span class="line"></span><br><span class="line"> <span class="built_in">func</span>();</span><br><span class="line"> cout << <span class="string">"====================="</span> << endl;</span><br><span class="line"> <span class="keyword">for</span> (<span class="type">int</span> i = <span class="number">0</span>; i < <span class="number">200</span>; ++i) {</span><br><span class="line"> cout << a[i] << <span class="string">" "</span>;</span><br><span class="line"> }</span><br><span class="line"> cout << endl << <span class="string">"====================="</span> << endl;</span><br><span class="line"> <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure><p>输出：</p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line">root@<span class="number">3</span>eaa9392a3d9:/ubuntu/test_dir# ./a.out</span><br><span class="line"><span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span></span><br><span class="line">=====================</span><br><span class="line"><span class="keyword">sizeof</span> array <span class="number">40</span></span><br><span class="line">array[<span class="number">3</span>] <span class="number">1</span></span><br><span class="line">array[<span class="number">40</span>] <span class="number">3</span></span><br><span class="line">=====================</span><br><span class="line"><span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">3</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span> <span class="number">100</span></span><br><span class="line">=====================</span><br></pre></td></tr></tbody></table></figure><p>看代码输出，在函数内操作超过数组长度的内存没有什么影响，但是它却导致了上一级的数组 a [200] 里的内容被改变，因为数组使用的是栈内存，经过问题 1 的代码输出以及分析可以看出，栈帧内存是向下增长的，代码中操作了超过数组长度的内存地址，就影响到了之前栈帧的内存数据，导致之前栈内存数据出现错误，可能就会引发大 bug.</p><blockquote><p><strong>总结</strong></p></blockquote><p><strong>summary</strong></p><p>C++ 中数组长度可以是变量，但是不建议使用，因为数组使用的是栈内存，变量可以是个比较大的数，这样会导致 stack overflow, 建议使用堆内存.</p><p>操作超过数组长度的内存可以编译通过且表面上看不出来问题，但是会导致栈内存出现脏写，最终可能会引发难以排查的 bug,建议数组使用 std::array,操作超过长度的下标会抛异常有利于开发者及时发现错误.</p><p>▼</p><p>更多精彩推荐，请关注我们</p><p>▼</p><p><strong>代码精进之路 </strong></p><p>代码精进之路，我们一起成长！</p><p><img src="https://secure2.wostatic.cn/static/wtedawzen2SaSyA4ZQ87yB/image.png"></p><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kity.min.js"></script><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kityminder.core.min.js"></script><script defer="true" type="text/javascript" src="https://unpkg.com/[email protected]/dist/mindmap.min.js"></script><link rel="stylesheet" type="text/css" href="https://unpkg.com/[email protected]/dist/mindmap.min.css">]]></content>
<summary type="html"><p>转载：原创程序喵大人 程序喵大人 (微信公众号) (收录于话题:
C++ 精进之路)</p>
<p>推荐一下这个专题，讲 C++ 很棒</p></summary>
<category term="C++" scheme="https://fetasty.github.io/categories/C/"/>
<category term="C++" scheme="https://fetasty.github.io/tags/C/"/>
</entry>
<entry>
<title>C++ 中使用智能指针管理数组</title>
<link href="https://fetasty.github.io/posts/21ebbed9/"/>
<id>https://fetasty.github.io/posts/21ebbed9/</id>
<published>2022-02-20T14:27:59.000Z</published>
<updated>2023-06-19T08:50:18.902Z</updated>
<content type="html"><![CDATA[<p>C++ 智能指针不仅能管理普通对象，也可以管理数组对象</p><span id="more"></span><p>以前只知道使用智能指针管理对象</p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="function">std::unique_ptr<A> <span class="title">pA</span><span class="params">(<span class="keyword">new</span> A)</span></span>;</span><br><span class="line"><span class="comment">// do something with pA or pA.Get()</span></span><br><span class="line"><span class="comment">// 超过作用域后, pA自动释放资源</span></span><br></pre></td></tr></tbody></table></figure><p>智能指针也可以用于管理数组</p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">std::unique_ptr<<span class="type">int</span>[]> pArr;</span><br><span class="line">pArr.<span class="built_in">reset</span>(<span class="keyword">new</span> <span class="type">int</span>[<span class="number">10</span>]); <span class="comment">// pArr 管理10个大小的int数组</span></span><br><span class="line">pArr.<span class="built_in">reset</span>(<span class="keyword">new</span> <span class="type">int</span>[<span class="number">64</span>]); <span class="comment">// 替换pArr的管理数组, 原来的10大小的数组将被自动释放</span></span><br></pre></td></tr></tbody></table></figure><p>以上代码管理数组对象的 <code>reset</code> 方法在 C++17 之前不可用</p><figure class="highlight c++"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 特化 unique_ptr<T[]>的成员</span></span><br><span class="line"><span class="function"><span class="keyword">template</span><<span class="keyword">class</span> U></span></span><br><span class="line"><span class="function"><span class="type">void</span> <span class="title">reset</span><span class="params">(U)</span> </span>= <span class="keyword">delete</span>; <span class="comment">// C++17 前</span></span><br><span class="line"><span class="function"><span class="keyword">template</span><<span class="keyword">class</span> U></span></span><br><span class="line"><span class="function"><span class="type">void</span> <span class="title">reset</span><span class="params">(U)</span> <span class="keyword">noexcept</span></span>; <span class="comment">// C++17 起</span></span><br></pre></td></tr></tbody></table></figure><p>千万不要用普通的智能指针指向数组地址，否则可能内存泄漏！！</p><p><del><code>std::unique_ptr<int> p(new int[xx])</code></del>错误用法！</p><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kity.min.js"></script><script type="text/javascript" src="https://unpkg.com/[email protected]/dist/kityminder.core.min.js"></script><script defer="true" type="text/javascript" src="https://unpkg.com/[email protected]/dist/mindmap.min.js"></script><link rel="stylesheet" type="text/css" href="https://unpkg.com/[email protected]/dist/mindmap.min.css">]]></content>
<summary type="html"><p>C++ 智能指针不仅能管理普通对象，也可以管理数组对象</p></summary>
<category term="C++" scheme="https://fetasty.github.io/categories/C/"/>
<category term="C++" scheme="https://fetasty.github.io/tags/C/"/>
</entry>
</feed>