写入子进程的文件描述符 [英] Writing to child process file descriptor

问题描述

我有一个节目样本，这既需要从标准和非标准的文件描述符（3或4），如下图所示。

I have a program "Sample" which takes input both from stdin and a non-standard file descriptor (3 or 4) as shown below

int pfds[2];
pipe(pfds);    
printf("%s","\nEnter input for stdin");
read(0, pO, 5);    
printf("\nEnter input for fds 3");
read(pfds[0], pX, 5);

printf("\nOutput stout");
write(1, pO, strlen(pO));    
printf("\nOutput fd 4");
write(pfds[1], pX, strlen(pX));

现在我有另一个程序操作员，它使用execv在子进程中执行上述程序（样本）。现在，我想是通过经营者。

Now i have another program "Operator" which executes the above program(Sample) in a child process using execv. Now what i want is to send input to "Sample" through the "Operator" .

推荐答案

分叉子进程后，但之前调用的execve ，你必须调用 dup2（2）子进程标准输入描述重定向到管道的读端。下面是一个简单的一块code的没有太多的错误检查：

After forking the child process, but before calling execve, you'll have to call dup2(2) to redirect the child process' stdin descriptor to the read end of your pipe. Here is a simple piece of code without much error checking:

pipe(pfds_1); /* first pair of pipe descriptors */
pipe(pfds_2); /* second pair of pipe descriptors */

switch (fork()) {
  case 0: /* child */
    /* close write ends of both pipes */
    close(pfds_1[1]);
    close(pfds_2[1]);

    /* redirect stdin to read end of first pipe, 4 to read end of second pipe */
    dup2(pfds_1[0], 0);
    dup2(pfds_2[0], 4);

    /* the original read ends of the pipes are not needed anymore */
    close(pfds_1[0]);
    close(pfds_2[0]);

    execve(...);
    break;

  case -1:
    /* could not fork child */
    break;

  default: /* parent */
    /* close read ends of both pipes */
    close(pfds_1[0]);
    close(pfds_2[0]);

    /* write to first pipe (delivers to stdin in the child) */
    write(pfds_1[1], ...);
    /* write to second pipe (delivers to 4 in the child) */
    write(pfds_2[1], ...);
    break;
}

这你写从父进程第一管方式都将通过描述符传递到子进程 0 （标准输入），以及一切你从第二个管写将交付给描述符 4 以及

This way everything you write to the first pipe from the parent process will be delivered to the child process via descriptor 0 (stdin), and everything you write from the second pipe will be delivered to descriptor 4 as well.

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