Should '#include' and 'using' statements be repeated in both header and implementation files (C++)?

Question

I\'m fairly new to C++, but my understanding is that a #include statement will essentially just dump the contents of the #included file into the location of that statement. This

Answer 1

It's considered bad form to have a using statement in a header file at all, unless you are intentionally duplicating a symbol into a different namespace. It's ok to use in a cpp file.

Each typedef should exist only once in your codebase. That should be in a header file if it needs to be used in multiple cpp/h files. Duplicating them will cause you much grief.

A header file should have all the #include statements that it needs, and no others. If only pointers to a class are mentioned then use a forward declaration rather than including the header. Any other includes that are required only inside the cpp file should go there. Repeating the includes from the header is ok, but not required. It's just a style choice.