“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

You need to be careful when including headers inside of headers. In large projects, it can create a very tangled dependency chain that triggers larger/longer rebuilds than were actually necessary. Check out this article and its follow-up to learn more about the importance of good physical structure in C++ projects.

You should only include headers inside a header when absolutely needed (whenever the full definition of a class is needed), and use forward declaration wherever you can (when the class is required is a pointer or a reference).

As for namespaces, I tend to use the explicit namespace scoping in my header files, and only put a using namespace in my cpp files.