Should I use #include in headers?

Question

Is it necessary to #include some file, if inside a header (*.h), types defined in this file are used?

For instance, if I use GLib and wish to use the

Answer 1

Usually, library developers protect their includes from multiple including with the #ifndef /#define / #endif "trick" so you don't have to do it.

Of course, you should check... but anyways the compiler will tell you at some point ;-) It is anyhow a good practice to check for multiple inclusions since it slows down the compilation cycle.