Best practice for including from include files

Question

I was wondering if there is some pro and contra having include statements directly in the include files as opposed to have them in the source file.

Personally I like to

Answer 1

A header file is supposed to be treated like an API. Let us say you are writing a library for a client, you will provide them a header file for including in their code, and a compiled binary library for linking.

In such scenario, adding a '#include' directive in your header file will create a lot of problems for your client as well as you, because now you will have to provide unnecessary header files just to get stuff compiling. Forward declaring as much as possible enables cleaner API. It also enables your client to implement their own functions over your header if they want.

If you are sure that your header is never going to be used outside your current project, then either way is not a problem. Compilation time is also not a problem if you are using include guards, which you should have been using anyway.