如何在C ++中执行命令并获取命令的返回码stdout和stderr [英] How to execute a command and get return code stdout and stderr of command in C++

问题描述

给出以下答案（第一个c ++ 11答案）：

Given the following answer (first c++11 answer):

How to execute a command and get output of command within C++ using POSIX?

以下是为您方便起见的实现：

Here is the implementation for your convinience:

#include <cstdio>
#include <iostream>
#include <memory>
#include <stdexcept>
#include <string>
#include <array>

std::string exec(const char* cmd) {
    std::array<char, 128> buffer;
    std::string result;
    std::shared_ptr<FILE> pipe(popen(cmd, "r"), pclose);
    if (!pipe) throw std::runtime_error("popen() failed!");
    while (!feof(pipe.get())) {
        if (fgets(buffer.data(), 128, pipe.get()) != nullptr)
            result += buffer.data();
    }
    return result;
}

执行命令非常有效（例如 std :: string res = exec（ ls）; ）并将stdout转换为字符串。

This works really nicely to execute a command (e.g. std::string res = exec("ls");) and get the stdout into a string.

但是它不能做什么获取命令返回码（通过/失败整数）或stderr。理想情况下，我希望获得所有这三个代码（返回码，stdout，stderr）。

But what it does not do is get the command return code (pass/fail integer) or the stderr. Ideally I would like a way to get all three (return code, stdout, stderr).

我会选择stdout和stderr。我在想我需要添加另一个管道，但是我真的看不到如何设置第一个管道以获取stdout，因此我无法考虑如何对其进行更改以同时获得这两个管道。

I would settle for stdout and stderr. I am thinking that I need to add another pipe, but I can't really see how the first pipe is setup to get stdout so I can't think how I would change it to get both.

任何人都知道如何执行此操作，或者可能有其他可行的方法？

Any one got any ideas how to do that, or alternative approaches that may work?

更新

请参阅我的完整示例此处，并带有输出：

See my complete example here witht the output:

Start
1 res: /home

2 res: stdout

stderr
3 res: 
End

您可以看到 3 res：不会以与 2 res：stdout 相同的方式打印stderr，但是stderr只是转储到屏幕上

You can see that 3 res: does not print stderr in the same way that 2 res: stdout does, but stderr is just dumped onto the screen on a seperate line by the process (and not my program).

外部库

我真的不想使用诸如Qt和boost之类的外部库-主要是因为我想要它的可移植性以及我所从事的许多项目ork on不要使用boost。但是，我将标记包含这些选项的解决方案，因为它们对于其他用户有效：）

I really don't want to use external libraries like Qt and boost - mostly because I want the portability of it and also many projects that I work on don't use boost. However I will mark up solutions that contain these options as they are valid for other users :)

使用注释/答案完成解决方案

感谢您的回答/评论，以下是修改后的解决方案（可运行）：

Thanks all for your answers / comments, here is the modified solution (and runable):

工作解决方案

推荐答案

从 popen 的手册页：

The pclose() function waits for the associated process to terminate  and returns the exit status of the command as returned by wait4(2).

因此，自己调用 pclose（）（而不是使用 std :: shared_ptr<> 的destructor-magic可以为您提供流程的返回代码（如果流程尚未终止，则返回代码）。 / p>

So, calling pclose() yourself (instead of using std::shared_ptr<>'s destructor-magic) will give you the return code of your process (or block if the process has not terminated).

std::string exec(const char* cmd) {
    std::array<char, 128> buffer;
    std::string result;

    auto pipe = popen(cmd, "r"); // get rid of shared_ptr

    if (!pipe) throw std::runtime_error("popen() failed!");

    while (!feof(pipe)) {
        if (fgets(buffer.data(), 128, pipe) != nullptr)
            result += buffer.data();
    }

    auto rc = pclose(pipe);

    if (rc == EXIT_SUCCESS) { // == 0

    } else if (rc == EXIT_FAILURE) {  // EXIT_FAILURE is not used by all programs, maybe needs some adaptation.

    }
    return result;
}

使用 popen（）获取stderr和stdout ，恐怕您需要通过将 2>& 1 从传递给popen（）的命令行中将stderr的输出重定向到stdout。 code>。

Getting stderr and stdout with popen(), I'm afraid you'd need to redirect the output of stderr to stdout from the command-line you're passing to popen() by adding 2>&1. This has the inconvinience that both streams are unpredictably mixed.

如果确实要为stderr和stdout拥有两个杰出的文件描述符，那么一种方法是分叉自己，并将新进程stdout / stderr复制到可从父进程访问的两个管道中。 （请参见 dup2（）和 pipe（））。我可以在这里详细介绍，但这是一种很繁琐的处理方式，必须格外小心。互联网上到处都是例子。

If you really want to have two distinguished file-descriptors for stderr and stdout, one way to do it is to do the forking yourself and to duplicate the new processes stdout/stderr to two pipes which are accessible from the parent process. (see dup2() and pipe()). I could go into more detail here, but this is quite a tedious way of doing things and much care must be taken. And the internet is full of examples.

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