I am trying to write a header file. The reason I do this is because I want to test a library of functions, this file should itself not contain a main(). (Just to give you an idea of what I am trying to achieve).

So i have three files:
(1) messaging2.c (a set of useful functions)
(2) messaging2.h
(3) testMessaging.c (which includes #include "messaging2.h" and contains some tests)

Function signatures are included. However when I try to complie (3) i get:

testMessaging2. .text: undefined reference to '_checkMessage'
testMessaging2. .text: undefined reference to '_createMessage'

However, both signatures are in the header file (and in the original program file off course).

I know this is hard to answer without code, but before pasting a lot of code I'd thought I'd try to see if there is a very common cause for this other wise I will post the code.