Is it wrong to use C++ 'using' keyword in a header file?

Question

I\'ve been told it\'s bad to have \"using namespace ns123\" in a header file, but I can\'t remember what the reason given was. Is it in fact a bad thing to do, and why?

Answer 1

It will often give you strange and mysterious compilation errors, for one thing, where you can spend hours trying to figure out the root of the problem.