socketpair - a slight generalization of pipes used for two-way stream communication.

以下内容来自：匠意雕码 http://my.oschina.net/zengsai/blog/12583

今天用了一个从没玩过的socket函数socketpair()，它的作用是在进程内创建一对sock连接。乍一看好像也没什么，但是配合fork()使用之后就是各种欢乐。如下。

#define STRING1 "message from parent"
#define STRING2 "messgae from child"

#include <sys/types.h>

#include <sys/socket.h>
#include <stdio.h>
#include <errno.h>

main()
{
int sockets[2], child;
char buf[1024];

/* Get the socket pair */
if (socketpair(AF_UNIX, SOCK_STREAM,
0, sockets) < 0) {
printf("error %d on socketpair\n", errno);
exit(1);
}

/* create child process */
if ((child = fork()) == -1) {
printf("fork error %d\n", errno);
exit(1);
}

if (child != 0) { /* this is the parent */
/* close child's end of socket */
close(sockets[0]);

/* read message from child */
if (read(sockets[1], buf, sizeof(buf)) < 0) {
printf("error %d reading socket\n", errno);
exit(1);
}
printf("-->%s\n", buf);

/* write message to child */
if (write(sockets[1],
STRING1, sizeof(STRING1)) < 0) {
printf("error %d writing socket\n", errno);
exit(1);
}

/* finished */
close(sockets[1]);

} else { /* the child */

/* close parent's end of socket */
close(sockets[1]);

/* send message to parent */
if (write(sockets[0], STRING2,
sizeof(STRING1)) < 0) {

printf("error %d writing socket\n", errno);
exit(1);
}

/* get message from parent */

if (read(sockets[0],
buf, sizeof(buf)) < 0) {
printf("error %d reading socket\n", errno);
exit(1);
}
printf("-->%s\n", buf);

/* finished */
close(sockets[0]);
}
}