Question

Suppose I have the following defined in a header file:

namespace MyNamespace
{
   Class global_c;
}

Then I do this in a source file:

namespace MyNamespace
{
   void MyClass::Function( )
   {
       ::global_c.DoSomething( );
   }
}

global_c turns out as undefined by the compiler, if I do just global_c.DoSomething( ); however it compiles fine, if I add ‘using namespace MyNamespace;’ to the top of the file it also works fine.

Since global_c lives in the same namespace as ‘MyClass’ why can’t it be resolved just because ‘::’ is added to the front of it?

Answer 1

Because you are explicitly telling the compiler to use the global namespace by prepending the variable with ::. As global_c does not exist in the global namespace it throws an error.

The compiler is just doing what you told it to do. Think of :: as Global::.