C++: Namespaces -- How to use in header and source files correctly?

Question

Consider a pair of two source files: an interface declaration file (*.h or *.hpp) and its implementation file (*.cpp).

Let the *.h file be like the following:

namespace MyNamespace {   class MyClass {   public:     int foo();   }; } 

I have seen two different practices for using namespaces in source files:

*.cpp showing practice #1:

#include "MyClass.h" using namespace MyNamespace;  int MyClass::foo() { ... } 

*.cpp showing practice #2:

#include "MyClass.h" namespace MyNamespace {    int MyClass::foo() { ... }  } 

My question: Are there any differences between these two practices and is one considered better than the other?

Answer 1

From a code readability standpoint, it is probably better in my opinion to use the #2 method for this reason:

You can be using multiple namespaces at a time, and any object or function written below that line can belong to any of those namespaces (barring naming conflicts). Wrapping the whole file in a namespace block is more explicit, and allows you to declare new functions and variables that belong to that namespace within the .cpp file as well