How is a scope resolution operator '::' used specifically?

Question

Scope resolution operator in classes

Answer 1

When you are defining a class method outside the class, you have to resolve the scope so that the compiler knows the method of which class you are defining, e.g.

class A {
public:
void test(); // method declaration
};

void A::test() { std::cout << "Hello, David Chongo!"; }

For whatever reason, you might want to create a non-const static variable in your class:

class B {
public:
static int c;
/* static int c = 39; */ // error!
};
int B::c = 39; // valid

You may have also noticed that the scope resolution operator is also used to resolve namespaces, such as the standard namespace.

std::cout
std::cin
std::string

Just some trivia: You can also define your own namespaces, and use scope resolution operator in a similar fashion.

namespace Fermi {
int test = 39;
}

std::cout << Fermi::test;