Question

如何将第二个execlp("sort","sort,",(char *)0)输出到显示屏？

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dirent.h>
#include <sys/types.h>
#include <sys/stat.h>
#include "errno.h"

int main()
{
    int parprocID = getppid();//parent process id
    int c1Toc2[2];
    int c2Toc1[2];                            
    pipe(c1Toc2);//pipe 1, to child 2
    pipe(c2Toc1);//pipe 2, to child 1

    int cpid = 0;//child 1 pid
    int cpid2 = 0;//child 2 pid

    int child1,child2;//Child variable

    printf("Parent Process id is: %d.\n\n", parprocID);//parent pid introduction.

    child1 = fork();//creation of child 1
    if(child1 == 0)
    {
        cpid = getpid();
        printf("Child 1 created by process: %d has an id of %d.\n\n", parprocID, getpid());

        dup2(c1Toc2[1], STDOUT_FILENO);//redirect from stdout to pipe

        execlp("ls", "ls","-al","/bin", (char *)0);             

        exit(0);
    }
    else
    {
        child2=fork();  //creation of child 2   
        if(child2 == 0)
        {
            cpid2 = getpid();
            printf("Child 2 created by process: %d has an id of %d.\n", parprocID, getpid());

            dup2(c1Toc2[0], STDIN_FILENO);

            execlp("sort", "sort", (char *)0);
            exit(0);    
            close(c1Toc2[0]);
            close(c1Toc2[1]);   
        }
    }

    sleep(3);
    printf("PARENT: PROCESS waiting on children to complete\n");

    wait(NULL);
    wait(NULL);

    printf("Final print statement before exit\n");
    exit(0);
}

子级1具有execlps系统调用，因此子级1执行ls程序。 dup2将输出重定向到管道。我认为孩子2 execlp对ls进行排序，但代码只是挂起，我不确定我是否做得对，我期待孩子2显示孩子1重定向的内容。接下来会发生什么，或者我哪里出错？

Answer 1

父进程和子进程2（sort）也打开了管道的写入结束，因此sort正在等待其stdin上的更多输入：close(c1Toc2[1]);之前sleep(3);和execlp("sort", "sort", (char *)0);之前{{1}}必须添加{1}}。

如何使用execlp（）？

1 个答案: