重定向输入与输出 http://dev.rdxx.com/C/2005-9/13/202809468.shtml

矫情吗；* 2022-08-24 00:46 181阅读 0赞

大多数的IDE环境都具备这样一种功能，加载编译器编译好程序并执行，执行结果显示于IDE环境中的结果信息窗口，那么它是如何捕获程序运行结果的呢？其实简单地用dup/dup2重定位输出并通过管道获取该输出就可以达到这种效果。

#include <stdio.h>#include <unistd.h>#include <string.h>#include <errno.h>#include <sys/types.h>intmain(int argc, char **argv)
    {
       
        int fd[2];
        pid_t childpid;
    
        if (pipe(fd) == -1)
        {
       
            printf("%s: %d -- Create pipe error: %s/n", __FILE__, __LINE__, strerror(errno));
            exit(errno);
        }
    
        childpid = fork();
    
        if (childpid == -1)
        {
       
            printf("%s: %d -- fork error: %s/n", __FILE__, __LINE__, strerror(errno));
            exit(errno);
        }
    
        if (childpid == 0)
        {
       
            close(fd[0]);
    
            if (dup2(fd[1], STDOUT_FILENO) == -1)
            {
       
                printf("%s: %d -- dup2 error: %s/n", __FILE__, __LINE__, strerror(errno));
                exit(errno);
            }
    
            if (execlp("ls", "ls", "/", NULL) == -1)
            {
       
                printf("%s: %d -- execlp error: %s/n", __FILE__, __LINE__, strerror(errno));
                exit(errno);
            }
    
            exit(0);
        }
        else    {        char buff[4096];
    
            close(fd[1]);
            memset(buff, sizeof(buff), 0);
    
            printf("read %d bytes/n", read(fd[0], buff, sizeof(buff)));
            printf("output: %s/n", buff);
    
            exit(0);
        }
    }

以下代码则相反，重定向输入：

#include <stdio.h>#include <unistd.h>#include <string.h>#include <errno.h>#include <sys/types.h>#include <sys/wait.h>intmain(int argc, char **argv)
    {
       
        int fd[2];
        pid_t childpid;
    
        if (pipe(fd) == -1)
        {
       
            printf("%s: %d -- Create pipe error: %s/n", __FILE__, __LINE__, strerror(errno));
            exit(errno);
        }
    
        childpid = fork();
    
        if (childpid == -1)
        {
       
            printf("%s: %d -- fork error: %s/n", __FILE__, __LINE__, strerror(errno));
            exit(errno);
        }
    
        if (childpid == 0)
        {
       
            close(fd[1]);
            if (dup2(fd[0], STDIN_FILENO) == -1)
            {
       
                printf("%s: %d -- dup2 error: %s/n", __FILE__, __LINE__, strerror(errno));
                exit(errno);
            }
    
            if (execlp("xargs", "xargs", "ls", NULL) == -1)
            {
       
                printf("%s: %d -- execlp error: %s/n", __FILE__, __LINE__, strerror(errno));
                exit(errno);
            }
    
            exit(0);
        }
        else    {        int status;
    
            close(fd[0]);
            write(fd[1], "/", 1);
    
            printf("waitpid result: %d/n", waitpid(childpid, &status, WNOHANG));
            printf("status value: %d/n", status);
    
            if (WIFEXITED(status))
                printf("child process was terminated normally by calling exit or _exit/n");
            else if (WEXITSTATUS(status))
                printf("returns the exit status of the child by exit or _exit/n");
            else if (WIFSIGNALED(status))
                printf("child process was terminated by a signal/n");
            else if (WTERMSIG(status))
                printf("returns the number of the signal that caused the child process to terminate/n");
            else if (WCOREDUMP(status))
                printf("child produced a core dump/n");
            else if (WIFSTOPPED(status))
                printf("child process was stopped by delivery of a signal/n");
            else if (WSTOPSIG(status))

printf("retuns the number of the signal which caused the child to stop/n");
    else if (WIFCONTINUED(status))
    printf("child process was resumed by delivery of SIGCONT/n");
    exit(0);
    }
    }