“using namespace” in c++ headers

Question

In all our c++ courses, all the teachers always put using namespace std; right after the #includes in their .h files. This seems to me

Answer 1

Like all things in programming, pragmatism should win over dogmatism, IMO.

So long as you make the decision project-wide ("Our project uses STL extensively, and we don't want to have to prepend everything with std::."), I don't see the problem with it. The only thing you're risking is name collisions, after all, and with the ubiquity of STL it's unlikely to be a problem.

On the other hand, if it was a decision by one developer in a single (non-private) header-file, I can see how it would generate confusion among the team and should be avoided.