Enable the writing of ANSI escape codes on a file?

Question

I am struggling with a problem. I searched all around the web and StackOverflow website and found similar questions, but none of them provided me the answer I am searching.

I am on a Linux system (Ubuntu) and basically want to know how to write an ANSI escape code in an output file. For example, if I want to write a red string on the terminal I do:

cout << "\033[31m" << "Red string";

and it works. But if I want to write it on a .rtf file for example:

#include <iostream>
#include <fstream>
using namespace std;

ofstream os( "this_file.rtf" );
os << "\033[31m" << "Red string";
os.close();

it doesn't work and output in the file something like:

#[31mRed string

is there a way to enable the writing of an ANSI escape code on an output file like that one? Thanks.