Why I have to write std::cout and not also std::<<

Question

Why do I have to write std::cout and not also std::<< in a line of code like this:

#include 

int main() {
           


        

Answer 1

In std::cout << "Hello, world!"; //calls std:::operator <<

This is achieved with Argument-dependent name lookup (ADL, aka Koenig Lookup)

Although we have only one std qualifier but there are two things that comes up from std namespace

• cout
• <<

Without ADL, (Koenig Lookup)

std::cout std:: << "Hello World" ;//this won't compile

In order to compile it, we need to use it more uglier form

std::operator<<(std::cout, "Hello, world!");

So to avoid such ugly syntax we must appreciate Koenig Lookup :)