Linux进程间通信方式之socket使用实例
<p>套接字是一种通信机制，凭借这种机制，客户/服务器系统的开发工作既可以在本地单机上进行，也可以跨网络进行。<br>
套接字的特性有三个属性确定，它们是：域（domain），类型（type），和协议（protocol）。套接字还用地址作为它的名字。地址的格式随域（又被称为协议族，protocol family）的不同而不同。每个协议族又可以使用一个或多个地址族定义地址格式。</p>
<p>
<span><strong>1.套接字的域</strong></span></p>
<p>
域指定套接字通信中使用的网络介质。最常见的套接字域是AF_INET，它是指Internet网络，许多Linux局域网使用的都是该网络，当然，因特网自身用的也是它。其底层的协议——网际协议（IP）只有一个地址族，它使用一种特定的方式来指定网络中的计算机，即IP地址。</p>
<p>
在计算机系统内部，端口通过分配一个唯一的16位的整数来表示，在系统外部，则需要通过IP地址和端口号的组合来确定。</p>
<p>
<span><strong>2.套接字类型</strong></span></p>
<p>
流套接字（在某些方面类似域标准的输入/输出流）提供的是一个有序，可靠，双向字节流的连接。</p>
<p>
流套接字由类型SOCK_STREAM指定，它们是在AF_INET域中通过TCP/IP连接实现的。他们也是AF_UNIX域中常见的套接字类型。</p>
<p>
<strong>数据包套接字</strong></p>
<p>
与流套接字相反，由类型SOCK_DGRAM指定的数据包套接字不建立和维持一个连接。它对可以发送的数据包的长度有限制。数据报作为一个单独的网络消息被传输，它可能会丢失，复制或乱序到达。</p>
<p>
数据报套接字实在AF_INET域中通过UDP/IP连接实现，它提供的是一种无需的不可靠服务。</p>
<p>
<span><strong>3.套接字协议</strong></span></p>
<p>
只要底层的传输机制允许不止一个协议来提供要求的套接字类型，我们就可以为套接字选择一个特定的协议。</p>
<p>
先上一个代码</p>
<p>
服务端：</p>
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<code class="cpp comments">//s_unix.c </code>
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<code class="cpp preprocessor">#include <stdio.h> </code>
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<code class="cpp preprocessor">#include <sys/types.h> </code>
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<code class="cpp preprocessor">#include <sys/socket.h> </code>
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<code class="cpp preprocessor">#include <sys/un.h> </code>
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<code class="cpp preprocessor">#define UNIX_DOMAIN "/tmp/UNIX.domain" </code>
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<code class="cpp color1 bold">int</code> <code class="cpp plain">main(</code><code class="cpp keyword bold">void</code><code class="cpp plain">) </code>
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<code class="cpp plain">{ </code>
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<code class="cpp spaces"> </code><code class="cpp plain">socklen_t clt_addr_len; </code>
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<code class="cpp spaces"> </code><code class="cpp color1 bold">int</code> <code class="cpp plain">listen_fd; </code>
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<code class="cpp spaces"> </code><code class="cpp color1 bold">int</code> <code class="cpp plain">com_fd; </code>
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<code class="cpp spaces"> </code><code class="cpp color1 bold">int</code> <code class="cpp plain">ret; </code>
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<code class="cpp spaces"> </code><code class="cpp color1 bold">int</code> <code class="cpp plain">i; </code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">static</code> <code class="cpp color1 bold">char</code> <code class="cpp plain">recv_buf; </code>
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<code class="cpp spaces"> </code><code class="cpp color1 bold">int</code> <code class="cpp plain">len; </code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">struct</code> <code class="cpp plain">sockaddr_un clt_addr; </code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">struct</code> <code class="cpp plain">sockaddr_un srv_addr; </code>
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<code class="cpp spaces"> </code><code class="cpp plain">listen_fd=socket(PF_UNIX,SOCK_STREAM,0); </code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code><code class="cpp plain">(listen_fd<0) </code>
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<code class="cpp spaces"> </code><code class="cpp plain">{ </code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">perror</code><code class="cpp plain">(</code><code class="cpp string">"cannot create communication socket"</code><code class="cpp plain">); </code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">return</code> <code class="cpp plain">1; </code>
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<code class="cpp spaces"> </code><code class="cpp plain">} </code>
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<code class="cpp spaces"> </code><code class="cpp comments">//set server addr_param </code>
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<code class="cpp spaces"> </code><code class="cpp plain">srv_addr.sun_family=AF_UNIX; </code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">strncpy</code><code class="cpp plain">(srv_addr.sun_path,UNIX_DOMAIN,</code><code class="cpp keyword bold">sizeof</code><code class="cpp plain">(srv_addr.sun_path)-1); </code>
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<code class="cpp spaces"> </code><code class="cpp plain">unlink(UNIX_DOMAIN); </code>
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<code class="cpp spaces"> </code><code class="cpp comments">//bind sockfd & addr </code>
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<code class="cpp spaces"> </code><code class="cpp plain">ret=bind(listen_fd,(</code><code class="cpp keyword bold">struct</code> <code class="cpp plain">sockaddr*)&srv_addr,</code><code class="cpp keyword bold">sizeof</code><code class="cpp plain">(srv_addr)); </code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code><code class="cpp plain">(ret==-1) </code>
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<code class="cpp spaces"> </code><code class="cpp plain">{ </code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">perror</code><code class="cpp plain">(</code><code class="cpp string">"cannot bind server socket"</code><code class="cpp plain">); </code>
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<code class="cpp spaces"> </code><code class="cpp plain">close(listen_fd); </code>
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<code class="cpp spaces"> </code><code class="cpp plain">unlink(UNIX_DOMAIN); </code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">return</code> <code class="cpp plain">1; </code>
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<code class="cpp spaces"> </code><code class="cpp plain">} </code>
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<code class="cpp spaces"> </code><code class="cpp comments">//listen sockfd </code>
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<code class="cpp spaces"> </code><code class="cpp plain">ret=listen(listen_fd,1); </code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code><code class="cpp plain">(ret==-1) </code>
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<code class="cpp spaces"> </code><code class="cpp plain">{ </code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">perror</code><code class="cpp plain">(</code><code class="cpp string">"cannot listen the client connect request"</code><code class="cpp plain">); </code>
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<code class="cpp spaces"> </code><code class="cpp plain">close(listen_fd); </code>
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<code class="cpp spaces"> </code><code class="cpp plain">unlink(UNIX_DOMAIN); </code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">return</code> <code class="cpp plain">1; </code>
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<code class="cpp spaces"> </code><code class="cpp plain">} </code>
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<code class="cpp spaces"> </code><code class="cpp comments">//have connect request use accept </code>
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<code class="cpp spaces"> </code><code class="cpp plain">len=</code><code class="cpp keyword bold">sizeof</code><code class="cpp plain">(clt_addr); </code>
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<code class="cpp spaces"> </code><code class="cpp plain">com_fd=accept(listen_fd,(</code><code class="cpp keyword bold">struct</code> <code class="cpp plain">sockaddr*)&clt_addr,&len); </code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code><code class="cpp plain">(com_fd<0) </code>
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<code class="cpp spaces"> </code><code class="cpp plain">{ </code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">perror</code><code class="cpp plain">(</code><code class="cpp string">"cannot accept client connect request"</code><code class="cpp plain">); </code>
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<code class="cpp spaces"> </code><code class="cpp plain">close(listen_fd); </code>
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<code class="cpp spaces"> </code><code class="cpp plain">unlink(UNIX_DOMAIN); </code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">return</code> <code class="cpp plain">1; </code>
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<code class="cpp spaces"> </code><code class="cpp plain">} </code>
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<code class="cpp spaces"> </code><code class="cpp comments">//read and printf sent client info </code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">printf</code><code class="cpp plain">(</code><code class="cpp string">"/n=====info=====/n"</code><code class="cpp plain">); </code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">for</code><code class="cpp plain">(i=0;i<4;i++) </code>
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<code class="cpp spaces"> </code><code class="cpp plain">{ </code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">memset</code><code class="cpp plain">(recv_buf,0,1024); </code>
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<code class="cpp spaces"> </code><code class="cpp color1 bold">int</code> <code class="cpp plain">num=read(com_fd,recv_buf,</code><code class="cpp keyword bold">sizeof</code><code class="cpp plain">(recv_buf)); </code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">printf</code><code class="cpp plain">(</code><code class="cpp string">"Message from client (%d)) :%s/n"</code><code class="cpp plain">,num,recv_buf); </code>
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<code class="cpp spaces"> </code><code class="cpp plain">} </code>
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<code class="cpp spaces"> </code><code class="cpp plain">close(com_fd); </code>
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<code class="cpp spaces"> </code><code class="cpp plain">close(listen_fd); </code>
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<code class="cpp spaces"> </code><code class="cpp plain">unlink(UNIX_DOMAIN); </code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">return</code> <code class="cpp plain">0; </code>
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<code class="cpp plain">}</code>
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<code class="cpp comments">//c_unix.c</code>
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<code class="cpp preprocessor">#include <stdio.h></code>
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<code class="cpp preprocessor">#include <sys/types.h></code>
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<code class="cpp preprocessor">#include <sys/socket.h></code>
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<code class="cpp preprocessor">#include <sys/un.h></code>
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<code class="cpp preprocessor">#define UNIX_DOMAIN "/tmp/UNIX.domain"</code>
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<code class="cpp color1 bold">int</code> <code class="cpp plain">main(</code><code class="cpp keyword bold">void</code><code class="cpp plain">)</code>
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<div class="line number8 index7 alt1">
<code class="cpp plain">{</code>
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<code class="cpp spaces"> </code><code class="cpp color1 bold">int</code> <code class="cpp plain">connect_fd;</code>
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<code class="cpp spaces"> </code><code class="cpp color1 bold">int</code> <code class="cpp plain">ret;</code>
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<code class="cpp spaces"> </code><code class="cpp color1 bold">char</code> <code class="cpp plain">snd_buf;</code>
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<code class="cpp spaces"> </code><code class="cpp color1 bold">int</code> <code class="cpp plain">i;</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">static</code> <code class="cpp keyword bold">struct</code> <code class="cpp plain">sockaddr_un srv_addr;</code>
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<code class="cpp comments">//creat unix socket</code>
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<code class="cpp spaces"> </code><code class="cpp plain">connect_fd=socket(PF_UNIX,SOCK_STREAM,0);</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">if</code><code class="cpp plain">(connect_fd<0)</code>
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<code class="cpp spaces"> </code><code class="cpp plain">{</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">perror</code><code class="cpp plain">(</code><code class="cpp string">"cannot create communication socket"</code><code class="cpp plain">);</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">return</code> <code class="cpp plain">1;</code>
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<code class="cpp spaces"> </code><code class="cpp plain">} </code>
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<code class="cpp spaces"> </code><code class="cpp plain">srv_addr.sun_family=AF_UNIX;</code>
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<code class="cpp spaces"> </code><code class="cpp plain">ret=connect(connect_fd,(</code><code class="cpp keyword bold">struct</code> <code class="cpp plain">sockaddr*)&srv_addr,</code><code class="cpp keyword bold">sizeof</code><code class="cpp plain">(srv_addr));</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">perror</code><code class="cpp plain">(</code><code class="cpp string">"cannot connect to the server"</code><code class="cpp plain">);</code>
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<code class="cpp spaces"> </code><code class="cpp plain">close(connect_fd);</code>
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<code class="cpp spaces"> </code><code class="cpp keyword bold">return</code> <code class="cpp plain">1;</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">memset</code><code class="cpp plain">(snd_buf,0,1024);</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">strcpy</code><code class="cpp plain">(snd_buf,</code><code class="cpp string">"message from client"</code><code class="cpp plain">);</code>
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<code class="cpp comments">//send info server</code>
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<code class="cpp spaces"> </code><code class="cpp plain">write(connect_fd,snd_buf,</code><code class="cpp keyword bold">sizeof</code><code class="cpp plain">(snd_buf));</code>
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<code class="cpp spaces"> </code><code class="cpp plain">close(connect_fd);</code>
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<p>
使用套接字除了可以实现网络间不同主机间的通信外，还可以实现同一主机的不同进程间的通信，且建立的通信是双向的通信。socket进程通信与网络通信使用的是统一套接口，只是地址结构与某些参数不同。</p>
<p>
<span><strong>一、创建socket流程</strong></span></p>
<p>
<strong>（1）创建socket，类型为AF_LOCAL或AF_UNIX，表示用于进程通信：</strong></p>
<p>
创建套接字需要使用 socket 系统调用，其原型如下：</p>
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<code class="cpp color1 bold">int</code> <code class="cpp plain">socket(</code><code class="cpp color1 bold">int</code> <code class="cpp plain">domain, </code><code class="cpp color1 bold">int</code> <code class="cpp plain">type, </code><code class="cpp color1 bold">int</code> <code class="cpp plain">protocol);</code>
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其中，domain 参数指定协议族，对于本地套接字来说，其值须被置为 AF_UNIX 枚举值；type 参数指定套接字类型，protocol 参数指定具体协议；type 参数可被设置为 SOCK_STREAM（流式套接字）或 SOCK_DGRAM（数据报式套接字），protocol 字段应被设置为 0；其返回值为生成的套接字描述符。</p>
<p>
对于本地套接字来说，流式套接字（SOCK_STREAM）是一个有顺序的、可靠的双向字节流，相当于在本地进程之间建立起一条数据通道；数据报式套接字（SOCK_DGRAM）相当于单纯的发送消息，在进程通信过程中，理论上可能会有信息丢失、复制或者不按先后次序到达的情况，但由于其在本地通信，不通过外界网络，这些情况出现的概率很小。</p>
<p>
<span><strong>二、命名socket。</strong></span></p>
<p>
SOCK_STREAM 式本地套接字的通信双方均需要具有本地地址，其中服务器端的本地地址需要明确指定，指定方法是使用 struct sockaddr_un 类型的变量。</p>
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<code class="cpp keyword bold">struct</code> <code class="cpp plain">sockaddr_un {</code>
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<code class="cpp spaces"> </code><code class="cpp plain">sa_family_t sun_family; </code><code class="cpp comments">/* AF_UNIX */</code>
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<code class="cpp spaces"> </code><code class="cpp color1 bold">char</code> <code class="cpp plain">sun_path; </code><code class="cpp comments">/* 路径名 */</code>
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<p>
这里面有一个很关键的东西，socket进程通信命名方式有两种。一是普通的命名，socket会根据此命名创建一个同名的socket文件，客户端连接的时候通过读取该socket文件连接到socket服务端。这种方式的弊端是服务端必须对socket文件的路径具备写权限，客户端必须知道socket文件路径，且必须对该路径有读权限。</p>
<p>
另外一种命名方式是抽象命名空间，这种方式不需要创建socket文件，只需要命名一个全局名字，即可让客户端根据此名字进行连接。后者的实现过程与前者的差别是，后者在对地址结构成员sun_path数组赋值的时候，必须把第一个字节置0，即sun_path = 0，下面用代码说明：</p>
<p>
第一种方式：</p>
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<code class="cpp comments">//name the server socket </code>
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<code class="cpp spaces"> </code><code class="cpp plain">server_addr.sun_family = AF_UNIX;</code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">strcpy</code><code class="cpp plain">(server_addr.sun_path,</code><code class="cpp string">"/tmp/UNIX.domain"</code><code class="cpp plain">);</code>
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<code class="cpp spaces"> </code><code class="cpp plain">server_len = </code><code class="cpp keyword bold">sizeof</code><code class="cpp plain">(</code><code class="cpp keyword bold">struct</code> <code class="cpp plain">sockaddr_un);</code>
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<code class="cpp spaces"> </code><code class="cpp plain">client_len = server_len;</code>
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<p>
第二种方式：</p>
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<code class="cpp preprocessor">#define SERVER_NAME @socket_server</code>
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<code class="cpp spaces"> </code><code class="cpp plain">server_addr.sun_family = AF_UNIX; </code>
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<code class="cpp spaces"> </code><code class="cpp functions bold">strcpy</code><code class="cpp plain">(server_addr.sun_path, SERVER_NAME); </code>
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<code class="cpp spaces"> </code><code class="cpp plain">server_addr.sun_path=0; </code>
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<code class="cpp spaces"> </code><code class="cpp plain">server_len = </code><code class="cpp functions bold">strlen</code><code class="cpp plain">(SERVER_NAME) + offsetof(</code><code class="cpp keyword bold">struct</code> <code class="cpp plain">sockaddr_un, sun_path);</code>
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其中，offsetof函数在#include <stddef.h>头文件中定义。因第二种方式的首字节置0，我们可以在命名字符串SERVER_NAME前添加一个占位字符串，例如:</p>
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<code class="cpp preprocessor">#define SERVER_NAME @socket_server</code>
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前面的@符号就表示占位符，不算为实际名称。</p>
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提示：客户端连接服务器的时候，必须与服务端的命名方式相同，即如果服务端是普通命名方式，客户端的地址也必须是普通命名方式；如果服务端是抽象命名方式，客户端的地址也必须是抽象命名方式。</p>
<p>
<span><strong>三、绑定</strong></span></p>
<p>
SOCK_STREAM 式本地套接字的通信双方均需要具有本地地址，其中服务器端的本地地址需要明确指定，指定方法是使用 struct sockaddr_un 类型的变量，将相应字段赋值，再将其绑定在创建的服务器套接字上，绑定要使用 bind 系统调用，其原形如下：</p>
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<code class="cpp color1 bold">int</code> <code class="cpp plain">bind(</code><code class="cpp color1 bold">int</code> <code class="cpp plain">socket, </code><code class="cpp keyword bold">const</code> <code class="cpp keyword bold">struct</code> <code class="cpp plain">sockaddr *address, </code><code class="cpp color1 bold">size_t</code> <code class="cpp plain">address_len);</code>
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其中 socket表示服务器端的套接字描述符，address 表示需要绑定的本地地址，是一个 struct sockaddr_un 类型的变量，address_len 表示该本地地址的字节长度。实现服务器端地址指定功能的代码如下（假设服务器端已经通过上文所述的 socket 系统调用创建了套接字，server_sockfd 为其套接字描述符）：</p>
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<code class="cpp keyword bold">struct</code> <code class="cpp plain">sockaddr_un server_address;</code>
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<code class="cpp plain">server_address.sun_family = AF_UNIX;</code>
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<code class="cpp functions bold">strcpy</code><code class="cpp plain">(server_address.sun_path, </code><code class="cpp string">"Server Socket"</code><code class="cpp plain">);</code>
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<code class="cpp plain">bind(server_sockfd, (</code><code class="cpp keyword bold">struct</code> <code class="cpp plain">sockaddr*)&server_address, </code><code class="cpp keyword bold">sizeof</code><code class="cpp plain">(server_address));</code>
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客户端的本地地址不用显式指定，只需能连接到服务器端即可，因此，客户端的 struct sockaddr_un 类型变量需要根据服务器的设置情况来设置，代码如下（假设客户端已经通过上文所述的 socket 系统调用创建了套接字，client_sockfd 为其套接字描述符）：</p>
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<span><strong>四、监听</strong></span></p>
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服务器端套接字创建完毕并赋予本地地址值（名称，本例中为Server Socket）后，需要进行监听，等待客户端连接并处理请求，监听使用 listen 系统调用，接受客户端连接使用accept系统调用，它们的原形如下：</p>
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<code class="cpp color1 bold">int</code> <code class="cpp plain">listen(</code><code class="cpp color1 bold">int</code> <code class="cpp plain">socket, </code><code class="cpp color1 bold">int</code> <code class="cpp plain">backlog);</code>
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<code class="cpp color1 bold">int</code> <code class="cpp plain">accept(</code><code class="cpp color1 bold">int</code> <code class="cpp plain">socket, </code><code class="cpp keyword bold">struct</code> <code class="cpp plain">sockaddr *address, </code><code class="cpp color1 bold">size_t</code> <code class="cpp plain">*address_len);</code>
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其中 socket 表示服务器端的套接字描述符；backlog 表示排队连接队列的长度（若有多个客户端同时连接，则需要进行排队）；address 表示当前连接客户端的本地地址，该参数为输出参数，是客户端传递过来的关于自身的信息；address_len 表示当前连接客户端本地地址的字节长度，这个参数既是输入参数，又是输出参数。实现监听、接受和处理的代码如下：</p>
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<code class="cpp spaces"> </code><code class="cpp plain">server_client_sockfd = accept(server_sockfd, (</code><code class="cpp keyword bold">struct</code> <code class="cpp plain">sockaddr*)＆server_client_address, &server_client_length);</code>
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这里使用死循环的原因是服务器是一个不断提供服务的实体，它需要不间断的进行监听、接受并处理连接，本例中，每个连接只能进行串行处理，即一个连接处理完后，才能进行后续连接的处理。如果想要多个连接并发处理，则需要创建线程，将每个连接交给相应的线程并发处理。</p>
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客户端套接字创建完毕并赋予本地地址值后，需要连接到服务器端进行通信，让服务器端为其提供处理服务。对于 SOCK_STREAM 类型的流式套接字，需要客户端与服务器之间进行连接方可使用。连接要使用 connect 系统调用，其原形为</p>
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<code class="cpp color1 bold">int</code> <code class="cpp plain">connect(</code><code class="cpp color1 bold">int</code> <code class="cpp plain">socket, </code><code class="cpp keyword bold">const</code> <code class="cpp keyword bold">struct</code> <code class="cpp plain">sockaddr *address, </code><code class="cpp color1 bold">size_t</code> <code class="cpp plain">address_len);</code>
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其中socket为客户端的套接字描述符，address表示当前客户端的本地地址，是一个 struct sockaddr_un 类型的变量，address_len 表示本地地址的字节长度。实现连接的代码如下：</p>
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<code class="cpp plain">connect(client_sockfd, (</code><code class="cpp keyword bold">struct</code> <code class="cpp plain">sockaddr*)&client_address, </code><code class="cpp keyword bold">sizeof</code><code class="cpp plain">(client_address));</code>
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无论客户端还是服务器，都要和对方进行数据上的交互，这种交互也正是我们进程通信的主题。一个进程扮演客户端的角色，另外一个进程扮演服务器的角色，两个进程之间相互发送接收数据，这就是基于本地套接字的进程通信。发送和接收数据要使用 write 和 read 系统调用，它们的原形为：</p>
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<code class="cpp color1 bold">int</code> <code class="cpp plain">read(</code><code class="cpp color1 bold">int</code> <code class="cpp plain">socket, </code><code class="cpp color1 bold">char</code> <code class="cpp plain">*buffer, </code><code class="cpp color1 bold">size_t</code> <code class="cpp plain">len);</code>
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<code class="cpp color1 bold">int</code> <code class="cpp plain">write(</code><code class="cpp color1 bold">int</code> <code class="cpp plain">socket, </code><code class="cpp color1 bold">char</code> <code class="cpp plain">*buffer, </code><code class="cpp color1 bold">size_t</code> <code class="cpp plain">len);</code>
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其中 socket 为套接字描述符；len 为需要发送或需要接收的数据长度；对于 read 系统调用，buffer 是用来存放接收数据的缓冲区，即接收来的数据存入其中，是一个输出参数；对于 write 系统调用，buffer 用来存放需要发送出去的数据，即 buffer 内的数据被发送出去，是一个输入参数；返回值为已经发送或接收的数据长度。例如客户端要发送一个 "Hello" 字符串给服务器，则代码如下：</p>
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<code class="cpp plain">write(client_sockfd, buffer, </code><code class="cpp functions bold">strlen</code><code class="cpp plain">(buffer));</code>
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交互完成后，需要将连接断开以节省资源，使用close系统调用，其原形为：</p>
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<code class="cpp color1 bold">int</code> <code class="cpp plain">close(</code><code class="cpp color1 bold">int</code> <code class="cpp plain">socket);</code>
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不多说了，直接使用，大家一定都会，呵呵！</p>
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上面所述的每个系统调用都有 -1 返回值，在调用不成功时，它们均会返回 -1，这个特性可以使得我们用 if - else 或异常处理语句来处理错误，为我们提供了很大的方便。</p>
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SOCK_DGRAM 数据报式本地套接字的应用场合很少，因为流式套接字在本地的连接时间可以忽略，所以效率并没有提高，而且发送接收都需要携带对方的本地地址，因此很少甚至几乎不使用。</p>
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与本地套接字相对应的是网络套接字，可以用于在网络上传送数据，换言之，可实现不同机器上的进程通信过程。在 TCP/IP 协议中，IP 地址的首字节为 127 即代表本地，因此本地套接字通信可以使用 IP 地址为 127.x.x.x 的网络套接字来实现。</p>
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<span><strong>总结</strong></span></p>
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以上就是本文关于Linux进程间通信方式之socket使用实例的全部内容，希望对大家有所帮助。感谢朋友们对本站的支持。</p>
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原文链接：http://blog.csdn.net/shanzhizi/article/details/16882087</p>
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