Unit tests for C++ criterion

I’m trying to make unit tests with criterion for my C++ code but I can’t figure out how to test a function that only print and do not return anything. Here’s what I tried:

//the function to test

#include <iostream>
#include <fstream>

void my_cat(int ac, char **av)
{
    if (ac <= 1)
        std::cout << "my_cat: Usage: ./my_cat file [...]" << std::endl;
    for (unsigned i = 1; i < ac; i += 1) {
        std::ifstream file (av[i]);
        if (file.fail()) {
            std::cout << "my_cat: ";
            std::cout << av[i];
            std::cout << ": No such file or directory" << std::endl;
        }
        else if (file.is_open()) {
            std::cout << file.rdbuf() << std::endl;
        }
        file.close();
    }
}

//the test
#include  <criterion/criterion.h>
#include  <criterion/redirect.h>

void my_cat(int ac, char **av);

Test(mycat, my_cat)
{
    char *av[] = {"./my_cat", "text.txt"};
    my_cat(2, av);
}

But now that I’m here I don’t know what to use to check if the print is correct.

>Solution :

With gtest, I think this can help you

testing::internal::CaptureStdout();
std::cout << "My test";
std::string output = testing::internal::GetCapturedStdout();

refer from : How to capture stdout/stderr with googletest?