Thread: Namespace std

Is it better to use

Code:

using namespace std;

or

Code:

using std::cout;
using std::cin;
//ect.

or maybe

Code:

std::cout << "What should I use?\n";
std::cin >> the.answer;

Which of the following is considered 'better coding'?

or should I possibly learn to use 'printf'?

thanks in advance

I recommend the second example.

Kuphryn

It all depends on how usefull you will find naming something "cout". The trade-offs are.

using namespace std;

I can't use vector, less, set, swap, greater, max, min, or count as names for anything.

using std::cout;

you can use any name except cout, however you cannot cut-and-paste a block of code that contains an unqualified cout. This sort of using is generally fine anywhere except headers, if your headers need any using's you should strongly consider wrapping them in your own namespace (feel free to polute the hell out of your own namespace, typedef int i; if you want)

std::cout << "x = " << std::setw(5) << std::precision(4) << x << std::end;

is ugly, but always safe.

It depends on what you're doing. The only time I ever "use" an entire namespace ("using namespace std") is for quick testing programs, because I don't think it's a good idea. As you probably guessed from experience with cout, it allows you to call all the standard functions (and access objects) without qualifying them. This is bad if, for example, you want to create a function called "abs" but didn't realize that there's already a standard one by that name.

I usually use the second method as well, because I know enough that if I'm "using" a std object not to create my own with the same name. I prefer to use the third method if I'm not going to be using a lot of something, i.e. just one or two calls to cout, but that's because I'm paranoid.

Although it can't hurt to know, printf is rarely (if ever) used (in my own experience, anyway). Streams are usually more convenient and more powerful.