akbiggs akbiggs - 6 months ago 29
C++ Question

Why is "using namespace std" in C++ considered bad practice?

I've been told by others on numerous occasions that my teacher's advice of exercising

using namespace std
in code was wrong. Hence, we should use

Why is
using namespace std
considered bad practice? Is it really that inefficient or risk declaring ambiguous variables (variables that share the same name as a function in
namespace)? Or, does this impact performance?


This is not related to performance at all. But consider this: you are using two libraries called Foo and Bar:

using namespace foo;
using namespace bar;

Everything works fine, you can call Blah() from Foo and Quux() from Bar without problems. But one day you upgrade to a new version of Foo 2.0, which now offers a function called Quux(). Now you've got a conflict: Both Foo 2.0 and Bar import Quux() into your global namespace. This is going to take some effort to fix, especially if the function parameters happen to match.

If you had used foo::Blah() and bar::Quux(), then the introduction of foo::Quux() would have been a non-event.