父子进程之间管道通信问题

[曳尾之鱼]

看不懂这个程序输出的结果,求解释：

源代码：
esperantor@ubuntu:~/source$ cat noname_pipe_example.c
#include	<unistd.h>
#include	<stdio.h>
#include	<stdlib.h>

int main(int argc,char **argv)
{
	pid_t	pid;
	int		temp;
	int 	pipedes[2];
	char	s[13] = "test message!";
	char	d[13];

	if ((pipe(pipedes))== -1)
	{
		perror("pipe");
		exit(EXIT_FAILURE);
	}

	if ((pid=fork()) == -1)
	{
		perror("fork");
		exit(EXIT_FAILURE);
	}
	else if(pid==0)
	{
		printf("now ,write data to pipe\n");
		if ((write(pipedes[1],s,13)) == -1)
				{
					perror("write");
					exit(EXIT_FAILURE);
				}
				else
				{
					printf("the written data is :%s\n",s);
					exit(EXIT_SUCCESS);
				}
	}
	else if (pid >0)
	{
		sleep(2);
		printf("now,read data from pipe\n");
		
		if ((read(pipedes[0],d,13))==-1)
		{
			perror("read");
			exit(EXIT_FAILURE);
		}
		printf("the data from pipe is :%s\n",d);
	}
	return 0;
}



结果：
esperantor@ubuntu:~/source$ gcc -o noname_pipe_example noname_pipe_example.c
esperantor@ubuntu:~/source$ ./noname_pipe_example
now ,write data to pipe
the written data is :test message!
now,read data from pipe
the data from pipe is :test message!test message!

怎么会输出2个输入字符串(test message!)呢？

[guoxuqu]

我修改了一下，现在已经正常了,修改地方我有标出

#include    <unistd.h>
#include    <stdio.h>
#include    <stdlib.h>

int main(int argc,char **argv)
{
    pid_t    pid;
    int        temp;
    int     pipedes[2];
    char    s[14] = "test message!";//这里数组长度应该为14，包括字符串结速符
    char    d[13];

    if ((pipe(pipedes))== -1)
    {
        perror("pipe");
        exit(EXIT_FAILURE);
    }

    if ((pid=fork()) == -1)
    {
        perror("fork");
        exit(EXIT_FAILURE);
    }
    else if(pid==0)
    {
        printf("now ,write data to pipe\n");
        if ((write(pipedes[1],s,14)) == -1)//这里长度13改为14
                {
                    perror("write");
                    exit(EXIT_FAILURE);
                }
                else
                {
                    printf("the written data is :%s\n",s);
                    exit(EXIT_SUCCESS);
                }
    }
    else if (pid >0)
    {
        sleep(2);
        printf("now,read data from pipe\n");
        
        if ((read(pipedes[0],d,14))==-1)//这里长度13改为14
        {
            perror("read");
            exit(EXIT_FAILURE);
        }
        printf("the data from pipe is :%s\n",d);
    }
    return 0;
}

[guoxuqu]

因为字符串包括空结束符'\0'的长度是14，原来子进程往管道写入时没有写入空结束符，父进程从管道中读时也没有读到字符串,而printf打印字符串时是碰到空结束符才结束。

[guoxuqu]

在栈里面s数组是存放在d数组后面，所以会打印出两个2个输入字符串(test message!)

[曳尾之鱼]

[Quote=引用 1 楼 guoxuqu 的回复:]

我修改了一下，现在已经正常了,修改地方我有标出
C/C++ code
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

int main(int argc,char **argv)
{
pid_t pid;
int temp;
int pipedes[2……
[/Quote]

嗯
有道理

调试了下，是正确的

谢谢啊