Linux网络编程 -- socketpair的使用

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Ai_Yang 2022-03-16 10:41:12 博主文章分类：Nginx

socketpair的使用

Linux实现了一个源自BSD的socketpair调用，可以实现在同一个文件描述符中进行读写的功能。

该系统调用能创建一对已连接的UNIX族socket。

在Linux中，完全可以把这一对socket当成pipe返回的文件描述符一样使用，唯一的区别就是这一对文件描述符中的任何一个都可读和可写，函数原型如下：

<code class="hljs vala has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <sys/types.h></span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <sys/socket.h></span>

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> socketpair(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> domain, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> type, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> protocol, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> sv[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>]);</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

socketpair()函数建立一对匿名的已经连接的套接字，其特性由协议族d、类型type、协议protocol决定，建立的两个套接字描述符会放在sv[0]和sv[1]中。

socketpair函数参数说明：

第1个参数domain，表示协议族，只能为AF_LOCAL或者AF_UNIX。

第2个参数type，表示协议，可以是SOCK_STREAM或者SOCK_DGRAM。用SOCK_STREAM建立的套接字对是管道流，与一般的管道相区别的是，套接字对建立的通道是双向的，即每一端都可以进行读写。

第3个参数protocol，表示类型，只能为0。

第4个参数sv[2]是接收代表两个套接口的整数数组。每一个文件描述符代表一个套接口，并且与另一个并没有区别。

函数返回值：

如果函数成功，将会返回0值。否则将会返回-1表明创建失败，并且errno来表明特定的错误号。

以下给出个简单的例子，通过socketpair实现父子间进程通信：

<code class="hljs ocaml has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*socketpair1.c*/</span>
#<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">include</span> <sys/types.h>
#<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">include</span> <sys/socket.h>
#<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">include</span> <stdlib.h>
#<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">include</span> <stdio.h>

<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">int</span> main ()
{
    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">int</span> fd[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>];
    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">int</span> r = socketpair(AF_UNIX, SOCK_STREAM, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>, fd);
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (r < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>){
        perror( <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"socketpair()"</span> );
        exit(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>);
    }

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (fork()){ <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 父进程 */</span>
        <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">int</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">val</span> = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
        close(fd[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>]);
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span> (<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>){
            sleep(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>);
            ++<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">val</span>;
            printf(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"发送数据: %d\n"</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">val</span>);
            write(fd[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>], &<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">val</span>, sizeof(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">val</span>));
            read(fd[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>], &<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">val</span>, sizeof(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">val</span>));
            printf(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"接收数据: %d\n"</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">val</span>);
        }
    }<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span>{  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*子进程*/</span>
        <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">int</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">val</span>;
        close(fd[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>]);
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>){
            read(fd[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>], &<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">val</span>, sizeof(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">val</span>));
            ++<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">val</span>;
            write(fd[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>], &<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">val</span>, sizeof(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">val</span>));
        }
    }
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li></ul>

执行结果：

<code class="hljs ruby has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">yu<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">@ubuntu</span><span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:~/Linux/</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">217</span>/pro_pool/socketpair<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">$ </span>vi socketpair1.c
yu<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">@ubuntu</span><span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:~/Linux/</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">217</span>/pro_pool/socketpair<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">$ </span>gcc -o socketpair1 socketpair1.c
yu<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">@ubuntu</span><span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:~/Linux/</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">217</span>/pro_pool/socketpair<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">$ </span>./socketpair1
发送数据<span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>
接收数据<span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>
发送数据<span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>
接收数据<span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>
发送数据<span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>
接收数据<span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">6</span>
...</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>

分析程序：一开始由socketpair创建一个套接字对，父进程关闭fd[1]，子进程关闭fd[0]，父进程sleep(1)让子进程先执行，子进程read(fd[1], &val, sizeof(val))阻塞，然后父进程write(fd[0]..)发送数据，子进程接收数据处理后再发送给父进程数据write(fd[1]..)，父进程读取数据，打印输出。（注意:socketpair产生的套接字对实现全双工通信）

sendmsg, recvmsg , send函数的使用

sendmsg, recvmsg , send三个函数的头文件：

<code class="hljs vala has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <sys/types.h>  </span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <sys/socket.h></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li></ul>

sendmsg函数

定义函数

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> sendmsg(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> s, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> strcut msghdr *msg, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">unsigned</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> flags);</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

函数说明：sendmsg()用来将数据由指定的socket传给对方主机.

参数s：为已建立好连线的socket, 如果利用UDP协议则不需经过连线操作.

参数msg：指向欲连线的数据结构内容, 参数flags 一般默认为0, 详细描述请参考send().

返回值：成功返回发送的字节数，出错返回-1

recvmsg函数

定义函数

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> recvmsg(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> s, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> msghdr *msg, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">unsigned</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> flags);</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

函数说明：recvmsg()用来接收远程主机经指定的socket 传来的数据.

参数s 为已建立好连线的socket, 如果利用UDP 协议则不需经过连线操作.

参数msg 指向欲连线的数据结构内容,

参数flags 一般设0, 详细描述请参考send().

返回值：成功则返回接收到的字符数, 失败则返回-1, 错误原因存于errno 中.

send函数

定义函数：int send(int s, const void * msg, int len, unsigned int falgs);

函数说明：send()用来将数据由指定的socket 传给对方主机.

参数s 为已建立好连接的socket.

参数msg 指向欲连线的数据内容.

参数len 则为数据长度.

参数flags 一般设0, 其他数值定义如下：

MSG_OOB 传送的数据以out-of-band 送出.

MSG_DONTROUTE 取消路由表查询

MSG_DONTWAIT 设置为不可阻断运作

MSG_NOSIGNAL 此动作不愿被SIGPIPE 信号中断.

返回值：成功则返回实际传送出去的字符数, 失败返回-1. 错误原因存于errno.

结构msghdr定义如下：

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> msghdr
{
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> *msg_name; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//发送或接收数据的地址</span>
    socklen_t msg_namelen; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//地址长度</span>
    strcut iovec * msg_iov; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//要发送或接受数据</span>
    size_t msg_iovlen; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//容器数据长度</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> * msg_control; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//附属数据</span>
    size_t msg_controllen; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//附属数据长度</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> msg_flags; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//接收消息的标志</span>
};</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>

返回值：成功则返回实际传送出去的字符数, 失败返回-1, 错误原因存于errno

错误代码：

<code class="hljs livecodeserver has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>、EBADF 参数s 非合法的<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">socket</span> 处理代码.
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>、EFAULT 参数中有一指针指向无法存取的内存空间
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>、ENOTSOCK 参数s 为一文件描述词, 非<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">socket</span>.
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>、EINTR 被信号所中断.
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>、EAGAIN 此操作会令进程阻断, 但参数s 的<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">socket</span> 为不可阻断.
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">6</span>、ENOBUFS 系统的缓冲内存不足
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">7</span>、ENOMEM 核心内存不足 EINVAL 传给系统调用的参数不正确.</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>

附属数据msg_control结构

控制信息头部本身由下面的C结构定义：

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> cmsghdr {
    socklen_t cmsg_len;
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>       cmsg_level;
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>       cmsg_type;
<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* u_char     cmsg_data[]; */</span>
};</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul>

其成员描述如下：

<code class="hljs bash has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">成员             描述
cmsg_len        附属数据的字节计数，这包含结构头的尺寸。这个值是由CMSG_LEN()宏计算的。
cmsg_level      这个值表明了原始的协议级别(例如，SOL_SOCKET)。
cmsg_<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">type</span>       这个值表明了控制信息类型(例如，SCM_RIGHTS)。
cmsg_data       这个成员并不实际存在，用来指明实际的额外附属数据所在的位置。</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

用sendmsg来传递数据程序实例

<code class="hljs cpp has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*sendmsg.c*/</span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <stdio.h></span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <stdlib.h></span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <unistd.h></span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <errno.h></span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <string.h></span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <sys/types.h></span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <sys/socket.h></span>

<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> main(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> argc,<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> *argv[])
{
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> ret;     <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 返回值 */</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> sock[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>];    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 套接字对 */</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> msghdr msg;
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> iovec iov[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>];
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> send_buf[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span>] = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"it is a test"</span>;
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> msghdr msgr;
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> iovec iovr[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>];
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> recv_buf[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span>];

    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 创建套接字对 */</span>
    ret = socketpair(AF_LOCAL,SOCK_STREAM,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>,sock);
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(ret == -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>){
        <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"socketpair err\n"</span>);
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;   
    }

    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* sock[1]发送数据到本地主机  */</span>
    bzero(&msg, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">sizeof</span>(msg));
    msg.msg_name = NULL;        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* void*类型 NULL本地地址*/</span>
    msg.msg_namelen = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
    iov[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>].iov_base = send_buf;
    iov[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>].iov_len = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">sizeof</span>(send_buf);
    msg.msg_iov = iov;<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//要发送或接受数据设为iov</span>
    msg.msg_iovlen = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//1个元素</span>

    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"开始发送数据：\n"</span>);
    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"发送的数据为: %s\n"</span>, send_buf);
    ret = sendmsg(sock[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>], &msg, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> );
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(ret == -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> ){
        <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"sendmsg err\n"</span>);
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;
    }
    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"发送成功！\n"</span>);

    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 通过sock[0]接收发送过来的数据 */</span>
    bzero(&msg, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">sizeof</span>(msg));
    msgr.msg_name = NULL;   
    msgr.msg_namelen = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
    iovr[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>].iov_base = &recv_buf;
    iovr[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>].iov_len = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">sizeof</span>(recv_buf);
    msgr.msg_iov = iovr;
    msgr.msg_iovlen = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;
    ret = recvmsg(sock[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>], &msgr, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>);
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(ret == -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> ){
        <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"recvmsg err\n"</span>);
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;
    }
    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"接收成功!\n"</span>);
    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"收到数据为: %s\n"</span>, recv_buf);

    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 关闭sockets */</span>
    close(sock[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>]);
    close(sock[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>]);

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li></ul>

执行程序结果：

<code class="hljs ruby has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">yu<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">@ubuntu</span><span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:~/Linux/</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">217</span>/pro_pool/socketpair<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">$ </span>gcc -o sendmsg sendmsg.c
yu<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">@ubuntu</span><span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:~/Linux/</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">217</span>/pro_pool/socketpair<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">$ </span>./sendmsg
开始发送数据：
发送的数据为<span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:</span> it is a test
发送成功！
接收成功!
收到数据为<span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">:</span> it is a test</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>

程序分析：由套接字sock[1]发数据到本地主机，由套接字sock[0]接收发送过来的数据。