Problem with stacked "#include"s

[Kaisky]

Hi!
I have a really small problem but no idea how to solve it.

So i have three classes "Polygon", "Surface" and "Edge".
All three of those classes need

#include "mathematics.h" 

in their header file because their declarations use a 4th class defined there.

Now "Polygon" itself also needs "Surface" and "Edge" in its header file, because it uses those.
But as soon as I double-include "mathematics.h" I get a ton of errors, starting with "redefinition".

My only solution would be to put all classes in one file, but then I would always include more than I need and the code would get messy.

How do I solve this smartly?

[Naughty Albatross]

> As soon as I double-include "mathematics.h" I get a ton of errors
Why did you double-include "mathematics.h" in a source file? Am I wrong?

[Kaisky]

To clarify:
in "Polygon.h" i need this:

#include "Edge.h"
#include "Surface.h" 

and in "Surface.h" i need:

#include "mathematics.h" 

and in "Edge.h" i need it as well:

#include "mathematics.h" 

That doesnt compile for me using Visual studios 2015. If i take out either

#include "Surface.h" 

or

#include "Edge.h" 

it works, but i need both classes.

[Naughty Albatross]

Firstly, you need to add some guard macros.

#ifndef MATHEMATICS_H
#define MATHEMATICS_H

// The rest of code in mathematics.h

#endif 

[Kaisky]

Thank you, now it works.

If I get the code fragmet right, it just does a ifclause for the compiler that skips the code if its already defined?

[Naughty Albatross]

Yes :)

[Naughty Albatross]

Glad it helped :)

[Kaisky]

thanks! <3