inline function in c

inline function definitions need to be visible wherever the function is invoked. You can define the function in a .c file if you only want to use it within that .c file, otherwise you need to define it in a .h file so that the definition can be #included wherever it is needed.

Yes. It can get messy though here is a good read: http://www.greenend.org.uk/rjk/2003/03/inline.html