Do you prefer explicit namespaces or 'using' in C++?

Question

When using C++ namespaces, do you prefer to explicitly name them, like this:

std::cout << \"Hello, world!\\n\";

Or do you prefer

Answer 1

I only use explicit namespaces when there's some ambiguity. It is more readable, but the extra typing is too tedious, and you have to assume other developers have a baseline level of familiarity with standard libraries.

The only other times I spell out a namespace are when I'm only using it once or twice, like adding in a quick debug statement, or if I'm using some non-standard library.

I typically declare the namespace at file scope, but if you're mixing namespaces it might make sense to put the declaration closer to the point where it's used, in function scope.

Answer 2

I tend to explicitly import the names that I need at the top of the .cpp file, so...

using std::cout; using std::endl;

etc...

That way I have control over the names that I use and it's easy to see where they come from and the code isn't cluttered at the point of use.

In the rare cases where I am using two names from different namespaces I fully qualify them at the point of use.

I always use fully qualified names in headers and hardly ever use 'using namespace x' anywhere...