An answer to this question on Stack Overflow.

Question

For example, if I use the following:

cout << "hello world";

Is there any way to know the size of what's being printed to stdout?

Answer

You can use std::stringstream for this:

#include <sstream>
#include <iostream>
int main(){
  std::stringstream ss;
  int a = 3;
  ss<<"Hello, world! "<<a<<std::endl;
  std::cout<<"Size was: "<<ss.str().size()<<std::endl;
  std::cout<<ss.str()<<std::endl;
}

The above returns 16: 14 character for "Hello, world!", 1 character for the contents of the variable a, and one character from std::endl.