popen() writes output of command executed to cout - c++

Question

I am writing an application that needs to open another process and get its output. Everywhere I've read online says I have to use popen and read from the file.
But I can't read from it. The output of the command gets outputted into the console window of the calling application. Below is the code I am using. I added some prints to debug.
#include <string>
#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <array>
int main()
{
// some command that fails to execute properly.
std::string command("ls afskfksakfafkas");
std::array<char, 128> buffer;
std::string result;
std::cout << "Opening reading pipe" << std::endl;
FILE* pipe = popen(command.c_str(), "r");
if (!pipe)
{
std::cerr << "Couldn't start command." << std::endl;
return 0;
}
while (fgets(buffer.data(), 128, pipe) != NULL) {
std::cout << "Reading..." << std::endl;
result += buffer.data();
}
auto returnCode = pclose(pipe);
std::cout << result << std::endl;
std::cout << returnCode << std::endl;
return 0;
}
Reading is never actually printed to my cout and result is an empty string. I clearly see the output of the command in my terminal. If the command exits gracefully the behaviour is as expected. But I only capture the output for error cases.

Answer 1

Popen doesn't capture stderr only stdout. Redirecting stderr to stdout fixes the issue.
#include <string>
#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <array>
int main()
{
std::string command("ls afskfksakfafkas 2>&1");
std::array<char, 128> buffer;
std::string result;
std::cout << "Opening reading pipe" << std::endl;
FILE* pipe = popen(command.c_str(), "r");
if (!pipe)
{
std::cerr << "Couldn't start command." << std::endl;
return 0;
}
while (fgets(buffer.data(), 128, pipe) != NULL) {
std::cout << "Reading..." << std::endl;
result += buffer.data();
}
auto returnCode = pclose(pipe);
std::cout << result << std::endl;
std::cout << returnCode << std::endl;
return 0;
}

Answer 2

You have to add "2>&1" at the end of command string
command.append(" 2>&1");
there is a full example https://www.jeremymorgan.com/tutorials/c-programming/how-to-capture-the-output-of-a-linux-command-in-c/