C-不使用popen的管道

问题描述

我该如何转换呢?

FILE *f;
char in_buffer[80];
f=popen("command","r");
fgets(in_buffer,sizeof(in_buffer),f)

不使用popen()，而仅使用pipe()或其他指令?

without using popen(), but only pipe() or other instruction?

推荐答案

这是我的简单实现，带有注释，说明正在做的事情.

Here's my simple implementation, with comments explaining what's being done.

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

FILE *
my_popen (const char *cmd)
{
    int fd[2];
    int read_fd, write_fd;
    int pid;               

    /* First, create a pipe and a pair of file descriptors for its both ends */
    pipe(fd);
    read_fd = fd[0];
    write_fd = fd[1];

    /* Now fork in order to create process from we'll read from */
    pid = fork();
    if (pid == 0) {
        /* Child process */

        /* Close "read" endpoint - child will only use write end */
        close(read_fd);

        /* Now "bind" fd 1 (standard output) to our "write" end of pipe */
        dup2(write_fd,1);

        /* Close original descriptor we got from pipe() */
        close(write_fd);

        /* Execute command via shell - this will replace current process */
        execl("/bin/sh", "sh", "-c", cmd, NULL);

        /* Don't let compiler be angry with us */
        return NULL;
    } else {
        /* Parent */

        /* Close "write" end, not needed in this process */
        close(write_fd);

        /* Parent process is simpler - just create FILE* from file descriptor,
           for compatibility with popen() */
        return fdopen(read_fd, "r");
    }
}

int main ()
{
    FILE *p = my_popen ("ls -l");
    char buffer[1024];
    while (fgets(buffer, 1024, p)) {
        printf (" => %s", buffer);
    }
    fclose(p);
}

注意:

1. 第三代码仅支持popen的"r"模式.实施其他模式(即"w"模式)留给读者练习.
2. 此示例中使用的系统功能可能会失败-错误处理留给读者练习.
3. pclose的实现留给读者练习-参见close，waiptid和fclose.

1. Thir code supports only "r" mode of popen. Implementing other modes, namely "w" mode is left as an exercise for the reader.
2. System functions used in this example may fail - error handling is left as an exercise for the reader.
3. Implementation of pclose is left as an exercise for the reader - see close, waiptid, and fclose.

如果您要查看实际的影响，则可以查看 OSX ， GNU glibc 和 OpenSolaris ，等等.

If you want to look at real impementations, you can look into sources of OSX, GNU glibc and OpenSolaris, among others.

希望这会有所帮助！

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