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.
#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(), static_cast<int>(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.
2024 Edit:
With newer versions of gnu g++ such as the one in Ubuntu 24.04, the code above results in an error because the std::unique_ptr
deleter is ignoring the return value from pclose()
.
error: ignoring attributes on template argument ‘int (*)(FILE*)’ [-Werror=ignored-attributes]
Had to modify the code to wrap pclose()
. Used a lambda for the wrapper. Now looks like this:
std::unique_ptr<FILE, void(*)(FILE*)> pipe(popen(cmd.c_str(), "r"),
[](FILE * f) -> void
{
// wrapper to ignore the return value from pclose() is needed with newer versions of gnu g++
std::ignore = pclose(f);
});