The Scope Resolution Operator consists of two colons :: and is used to specify which named context area, an identifier (variable, etc) is being referred to.

The named context area might be a function, class, struct, namespace.

For instance a class may have a number of members contained within its body code block, which can be referred to using the scope resolution operator, like so:

className :: member ;

If the className is omitted, it is assumed that the program's Global scope is being referred to, like so:

:: member ;

This example creates a global function, a namespace and a class all with unique returned values:

#include <iostream>
using namespace std;

int getValue(){
	return 21 ;
}

namespace mySpace {
	int getValue(){
		return 42 ;
	}
};

class myClass {
	public:
		static int getValue(){
			return 17 ;
		}
};

int main() {

	cout << "Global using :: to refer to getValue() = " << ::getValue() << endl ;
	cout << "Global no scope resolution, getValue() = " << getValue() << endl << endl ;

	cout << "Namespace referring to getValue() = " << mySpace::getValue() << endl << endl ;

	cout << "Now instantiating a myClass object" << endl ;

	myClass* ptr = new myClass() ;
	myClass myObject ;

	cout << "Class using -> to refer to getValue() = " << ptr->getValue() << endl ;
	cout << "Class using . member access to refer to getValue() = " << myObject.getValue() << endl ;
	cout << "Class using :: to refer to getValue() = " << myClass::getValue() << endl ;

	return 0;
}

Compile & Run: