:: without a namespace
:: in ::CGContextRef means global namespace, which means CGContextRef is defined in the global namespace.
int x = 10;
namespace test
{
int x = 100;
void f()
{
std::cout << x << std::endl; //prints 100
std::cout << ::x << std::endl; //prints 10
}
}
See complete demo here : http://www.ideone.com/LM8uo
The :: refers to the global namespace.
:: without any namespace name before it means it refers Global Namespace.
::CGContextRef cgContext = cocoa::createCgBitmapContext( surface );
means refer to CGContextRef in the Global Namespace.