Linux函数学习 fork

1、Linux fork 函数

pid_t fork(void);

pid_t ：对于子进程，返回0

pid_t ：对于父进程进程，返回子进程进程号

int pipe(int pipefd[2]);

pipefd[0] 为读取管道

pipefd[1] 为写入管道

返回值：-1失败 0 成功

2、函数实例

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <stdlib.h>
#include <string.h>


int main (int argc, char ** argv){

	int pipefd[2];
	int ret = 0;
	pid_t cpid;
	char buf;

	if(argc != 2) {
		printf("Usage pipe <command> \n");
		_exit(EXIT_SUCCESS);
	} else {
		printf("argv[1] = %s \n", argv[1]);
	}

	ret =  pipe(pipefd);

	if(ret == -1){
		perror("fork error \n");
	} else {
		printf("create pipe success !\n");
	}

	cpid = fork();	
	if (cpid == -1) {
		perror("fork error \n");
	}

	printf("pid1 = %d \n", getpid());
	
	if (cpid == 0) {	
		/*子进程从管道读取 */
		printf("child pid2 = %d cpid = %d \n", getpid(), cpid);
		/* 关闭不使用的写管道 */
		close(pipefd[1]);
	
		/*子进程读取管道数据，并输出打印*/
		while (read(pipefd[0], &buf, 1) > 0){
			write(STDOUT_FILENO, &buf, 1);
		}
		write(STDOUT_FILENO, "\n", 1);

		/*关闭管道*/
	    close(pipefd[0]);
		printf("child pid2 = %d cpid = %d \n", getpid(), cpid);
	   _exit(EXIT_SUCCESS);
   } else {
	   printf("parent pid3 = %d cpid = %d \n", getpid(), cpid);

	   /* 关闭不使用的读管道 */
	   close(pipefd[0]);

	   /* 父进程写arg[1]到管道 */
	   write(pipefd[1], argv[1], strlen(argv[1]));
	   close(pipefd[1]);
	
	   /*等待子进程*/
	   wait(NULL);
	   printf("parent pid3 = %d \n", getpid());
	   exit(EXIT_SUCCESS);
   }
	return 0;
}