Preprocessor directive #ifndef for C/C++ code

Question

In eclipse, whenever I create a new C++ class, or C header file, I get the following type of structure. Say I create header file example.h, I get this:

Answer 1

Consider this

File foo.c:

#include foo.h
#include bar.h

File bar.h

#include <iostream>
#include foo.h

Now, when we compile foo.c, we have foo.h in there twice! We definitely don't want this, because all the functions will throw compile errors the second time around.

To prevent this, we put the INCLUDE GUARD at the top. That way, if it's already been included, we define a preprocessor variable to tell us not to include it again.

It's very common (often mandated), and very frustrating if someone doesn't put one in there. You should be able to simply expect that each .h file has a header guard when you included. Of course, you know what they say when you assume things ("makes an ass of u and me") but that should be something you're expecting to see.