How do I execute a command and get the output of the command within C++ using POSIX?

Question

I am looking for a way to get the output of a command when it is run from within a C++ program. I have looked at using the system() function, but that will just execute a command. Here's an example of what I'm looking for:

std::string result = system("./some_command"); 

I need to run an arbitrary command and get its output. I've looked at boost.org, but I have not found anything that will give me what I need.

Answer 1

#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::unique_ptr<FILE, decltype(&pclose)> pipe(popen(cmd, "r"), pclose);     if (!pipe) {         throw std::runtime_error("popen() failed!");     }     while (fgets(buffer.data(), buffer.size(), pipe.get()) != nullptr) {         result += buffer.data();     }     return result; } 

Pre-C++11 version:

#include <iostream> #include <stdexcept> #include <stdio.h> #include <string>  std::string exec(const char* cmd) {     char buffer[128];     std::string result = "";     FILE* pipe = popen(cmd, "r");     if (!pipe) throw std::runtime_error("popen() failed!");     try {         while (fgets(buffer, sizeof buffer, pipe) != NULL) {             result += buffer;         }     } catch (...) {         pclose(pipe);         throw;     }     pclose(pipe);     return result; } 

Replace popen and pclose with _popen and _pclose for Windows.

Answer 2

Getting both stdout and stderr (and also writing to stdin, not shown here) is easy peasy with my pstreams header, which defines iostream classes that work like popen:

#include <pstream.h> #include <string> #include <iostream>  int main() {   // run a process and create a streambuf that reads its stdout and stderr   redi::ipstream proc("./some_command", redi::pstreams::pstdout | redi::pstreams::pstderr);   std::string line;   // read child's stdout   while (std::getline(proc.out(), line))     std::cout << "stdout: " << line << '\n';   # if reading stdout stopped at EOF then reset the state:   if (proc.eof() && proc.fail())     proc.clear();   // read child's stderr   while (std::getline(proc.err(), line))     std::cout << "stderr: " << line << '\n'; }