Scope Resolution Operator: :: 

You can tell the compiler to use the global identifier rather than the local identifier by prefixing the identifier with ::, the scope resolution operator.

:: identifier
class-name :: identifier
namespace :: identifier

Remarks

The identifier can be a variable or a function.

If you have nested local scopes, the scope resolution operator does not provide access to identifiers in the next outermost scope. It provides access to only the global identifiers.

Example

This example has two variables named amount. The first is global and contains the value 123. The second is local to the main function. The scope resolution operator tells the compiler to use the global amount instead of the local one.

// expre_ScopeResolutionOperator.cpp
// compile with: /EHsc
// Demonstrate scope resolution operator
#include <iostream>

using namespace std;

int amount = 123;   // A global variable

int main() {
   int amount = 456;   // A local variable
   cout  << ::amount << endl   // Print the global variable
         << amount << endl;    // Print the local variable
}

See Also

Reference

C++ Operators
Operator Precedence and Associativity
Namespaces (C++)
Names and Qualified Names