how to write log file in C++

I'll see the C answer given earlier and raise a C++ answer for the same thing:

#include <fstream>

void write_text_to_log_file( const std::string &text )
{
    std::ofstream log_file(
        "log_file.txt", std::ios_base::out | std::ios_base::app );
    log_file << text << std::end;
}

It'll do the same thing with the bonus that if the file fails to open for whatever reason it won't crash in a steaming heap of undefined behaviour.

Cheers,

Ash

PS the important bits of logging for when you write your own are:

- flush after every message - std::endl does that

- close the file after every message - the fstream destructor does that