管道是半双工的（一端只能读不能写，一端只能写不能读），但是可以通过创建两个管道来实现一个全双工（两端都可以读写）通信。
示例代码：
#include <stdio.h>
#include <unistd.h>
#include <strings.h>
#include <string.h>
#include <stdlib.h>
int main()
{
char* strc = "from parent's message";
char* strp = "from child's message";
char bufc[30];
char bufp[30];
bzero(bufc, sizeof(bufc));
bzero(bufp, sizeof(bufp));
pid_t pid;
int fd1[2];
int fd2[2];
pipe(fd1);
pipe(fd2);
pid = fork();
if(0 == pid)//child read
{
close(fd1[1]);
close(fd2[0]);
write(fd2[1], strp, strlen(strp)+1);
printf("child write work finish\n");
read(fd1[0], bufc, sizeof(bufc));
printf("child recv message:%s\n", bufc);
printf("child work finish\n");
close(fd1[0]);
close(fd2[1]);
exit(0);
}
else//parent write
{
close(fd1[0]);
close(fd2[1]);
write(fd1[1], strc, strlen(strc)+1);
printf("parent write work finish\n");
read(fd2[0], bufp, sizeof(bufp));
printf("parent recv message:%s\n", bufp);
printf("parent work finish\n");
close(fd1[1]);
close(fd2[0]);
wait(NULL);//
exit(0);
}
}