what is stdoutread in c++

#include <iostream>
#include <cstdio>
#include <cstring>

int main() {
    FILE* pipe = popen("ls", "r");
    if (!pipe) return 1;
    char buffer[128];
    std::string result = "";
    while (!feof(pipe)) {
        if (fgets(buffer, 128, pipe) != NULL)
            result += buffer;
    }
    pclose(pipe);
    std::cout << result.c_str();
    return 0;
}