Thread: What's "best practice" between 'using namespace std' and 'std::count/std::cin'

Never put a "using namespace" directive in a header file, in the global namespace. That's the best practice. I prefer not to use "using namespace" at all, but that's more a matter of personal preference.

It's not considered a good practice to be `using namespace` because of how C++ does overload resolution and you may get unintentional results if you're using a function that's defined in more than one namespace.

Instead, it's typically accepted to enumerate your `using`s so you'd type:

Code:

using std::vector;
using std::string;
using std::cout;
/* ... */

To this end, anyone reading your code can now know _exactly_ what functions you're importing from the namespace.

Edit:

The worst was when I was trying to read some code and they did this:

Code:

using namespace folly;
using namespace std;
using namespace proxygen;

Good luck looking up where each function comes from!

I don't think there is really a best practice about this. The only hard rule was written in this thread here.

Never put a "using namespace" directive in a header file, in the global namespace. That's the best practice.

Like stated earlier it can be a personal preference, and the rules of name lookup can force your hand. Programs will also look like crap if you convince yourself that one shortcut is better than another shortcut.

I don't really mind using namespace statements, but the only stance I can advocate for is doing what you have to do to get name resolution to work. You'll get into an internet argument if you care about this too much.

Yeah, never do it in a header file in global namespace, it can mess things up, but otherwise... I'd stick to using it as locally as I could, but as long as you know it won't screw you - you're probably fine.

using namespace std; always seemed like an easy cop-out for existing programs which suddenly had to deal with namespace aware compilers.

An easy one-line fix, and your programs still compiled.

But new code should take a much more refined approach to namespaces, especially when you have multiple namespaces in use at the same time.

Sure, having to write
std::cout << "hello world" << std::endl;
is a PITA, but no one is ever going to be in any doubt as to what you meant.

using std::cout; might be a comfortable half-way point if you use a lot of one particular aspect of a particular namespace.

Another thing that can sway a new coder one way or the other is
text books and colleges. Some of Deitel's older C++ books used to teach std::
prefix throughout. Their newer versions all teach using namespace std; as the
"standard", as they say. Not a major thing - but it can prevent some students new
to the language learning about other ways to include namespace objects into their
programs.

I think Salem was talking about from a programmers "too much to type" sort
of way, being having to put the std:: prefix before every namespace object etc.