c ++：subprocess输出到stdin [英] c++: subprocess output to stdin

问题描述

假设我想从我的程序中调用子进程，并且我想将该子进程的输出读入我的程序。

Suppose I want to call a subprocess from within my program, and I want to read the output from that subprocess into my program.

这里是一个简单的方法这样做：

Here is a trivial way to do that:

//somefile.cpp
system("sub_process arg1 arg2 -o file.out");
           //call the subprocess and have it write to file
FILE *f = std::fopen("file.out", "r");
//.... and so on

我们都知道i / o操作计算速度慢。为了加快速度，我想跳过写到文件然后从文件读取步骤，而是将这个子进程的输出直接重定向到 stdin / strong>（或其他流）

We all know that i/o operations are computationally slow. To speed this up, I would like to skip the write-to-file-then-read-from-file step, and instead redirect the output of this sub-process directly into stdin (or some other stream)

我该如何做？如何跳过i / o操作？

How would I do this? How do I skip the i/o operation?

注意：许多程序在运行时向stdout输出一些诊断信息，并将一个干净的输出写入stdout （例如：stdout：step1 ... done，step2 ... done，step3..done-o file-out：幻数是：47.28），所以忽略-o参数，输出将自动重定向到stdout不一定有帮助...

Note: many programs spit out some diagnostic stuff into stdout while they run, and write a clean version of the output to stdout (ex: stdout: "step1...done, step2...done, step3..done" -o file-out: "The magic number is: 47.28"), so ignoring the "-o " argument and trusting that output will be automatically re-directed to stdout isn't necessarily helpful...

感谢所有提前。

推荐答案

使用 popen 跳过文件，通过内存缓冲区获取命令的输出。

Using popen skips the file, and gets you command's output through an in-memory buffer.

#include <iomanip>
#include <iostream>
using namespace std;
const int MAX_BUFFER = 255;
int main() {
    string stdout;
    char buffer[MAX_BUFFER];
    FILE *stream = popen("command", "r");
    while ( fgets(buffer, MAX_BUFFER, stream) != NULL )
    stdout.append(buffer);
    pclose(stream);
    cout << endl << "output: " << endl << stdout << endl;
}

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