c++ - Linux 3.0 : Executing child process with piped stdin/stdout

在Linux 3.0/C++下:

我想要一个执行以下操作的函数:

string f(string s)
{
    string r = system("foo < s");
    return r;
}

显然上述方法不起作用，但是您可以理解。我有一个字符串s，我希望将其作为应用程序“foo”的子进程执行的标准输入传递，然后将其标准输出记录到字符串r中，然后将其返回。

我应该使用linux syscall或posix函数的什么组合？

最佳答案

eerpini提供的代码无法正常工作。请注意，例如，之后使用在父级中关闭的管端。看着

close(wpipefd[1]);

以及随后对该封闭描述符的写入。这只是换位，但它表明此代码从未使用过。以下是我测试过的版本。不幸的是，我更改了代码样式，因此这不被接受为对eerpini代码的编辑。

唯一的结构更改是，我仅重定向子级中的I/O(请注意dup2调用仅在子级路径中。)这非常重要，因为否则父级的I/O会困惑。感谢eerpini提出的最初答案，我在开发此答案时使用了它。

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

#define PIPE_READ 0
#define PIPE_WRITE 1

int createChild(const char* szCommand, char* const aArguments[], char* const aEnvironment[], const char* szMessage) {
  int aStdinPipe[2];
  int aStdoutPipe[2];
  int nChild;
  char nChar;
  int nResult;

  if (pipe(aStdinPipe) < 0) {
    perror("allocating pipe for child input redirect");
    return -1;
  }
  if (pipe(aStdoutPipe) < 0) {
    close(aStdinPipe[PIPE_READ]);
    close(aStdinPipe[PIPE_WRITE]);
    perror("allocating pipe for child output redirect");
    return -1;
  }

  nChild = fork();
  if (0 == nChild) {
    // child continues here

    // redirect stdin
    if (dup2(aStdinPipe[PIPE_READ], STDIN_FILENO) == -1) {
      exit(errno);
    }

    // redirect stdout
    if (dup2(aStdoutPipe[PIPE_WRITE], STDOUT_FILENO) == -1) {
      exit(errno);
    }

    // redirect stderr
    if (dup2(aStdoutPipe[PIPE_WRITE], STDERR_FILENO) == -1) {
      exit(errno);
    }

    // all these are for use by parent only
    close(aStdinPipe[PIPE_READ]);
    close(aStdinPipe[PIPE_WRITE]);
    close(aStdoutPipe[PIPE_READ]);
    close(aStdoutPipe[PIPE_WRITE]);

    // run child process image
    // replace this with any exec* function find easier to use ("man exec")
    nResult = execve(szCommand, aArguments, aEnvironment);

    // if we get here at all, an error occurred, but we are in the child
    // process, so just exit
    exit(nResult);
  } else if (nChild > 0) {
    // parent continues here

    // close unused file descriptors, these are for child only
    close(aStdinPipe[PIPE_READ]);
    close(aStdoutPipe[PIPE_WRITE]);

    // Include error check here
    if (NULL != szMessage) {
      write(aStdinPipe[PIPE_WRITE], szMessage, strlen(szMessage));
    }

    // Just a char by char read here, you can change it accordingly
    while (read(aStdoutPipe[PIPE_READ], &nChar, 1) == 1) {
      write(STDOUT_FILENO, &nChar, 1);
    }

    // done with these in this example program, you would normally keep these
    // open of course as long as you want to talk to the child
    close(aStdinPipe[PIPE_WRITE]);
    close(aStdoutPipe[PIPE_READ]);
  } else {
    // failed to create child
    close(aStdinPipe[PIPE_READ]);
    close(aStdinPipe[PIPE_WRITE]);
    close(aStdoutPipe[PIPE_READ]);
    close(aStdoutPipe[PIPE_WRITE]);
  }
  return nChild;
}