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Consider the following line of code:
::CGContextRef cgContext = cocoa::createCgBitmapContext( surface );
How come there's no namespace specified before :: ? Does that mean it's using the same namespace as the class you're in?
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All C++ standard library types and functions are declared in the std namespace or namespaces nested inside std thus it is widely used in most of the programs.
class can exists without namespace. class without namespace cannot be accessed in other namespace. Yes, namespace is used to just grouping and it is not mandatory.
Namespaces are basically just to organize your code. using namespace std; is used to inform the compiler to look for the io functions in this standard library. If it is not used, the compilation will flag an error that cin/cout is undefined. It is compiler dependent.
To put it as an advice: Do not use "using namespace" (std or other) at file scope in header files. It is OK to use it in implementation files.
:: 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
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