c++ - redirect output of an function printing to console to string

Question

lets say we have a function which prints text to the console and in which we do not have control over the source but we are able to call it. For example

void foo() {
    std::cout<<"hello world"<<std::endl; 
    print_to_console(); // this could be printed from anything
}

is it possible to redirect the output of the above function to a string without changing the function itself?

I'm not looking for a way to do this via terminal

Answer 1

Yes. That can be done. Here is a little demo:

#include <sstream>
#include <iostream>

void print_to_console() {
    std::cout << "Hello from print_to_console()" << std::endl;
}

void foo(){
  std::cout<<"hello world"<<std::endl; 
  print_to_console(); // this could be printed from anything
}
int main()
{
    std::stringstream ss;

    //change the underlying buffer and save the old buffer
    auto old_buf = std::cout.rdbuf(ss.rdbuf()); 

    foo(); //all the std::cout goes to ss

    std::cout.rdbuf(old_buf); //reset

    std::cout << "<redirected-output>
" 
              << ss.str() 
              << "</redirected-output>" << std::endl;
}

Output:

<redirected-output>
hello world
Hello from print_to_console()
</redirected-output>

See Online Demo.