include files

[madshov]

Hi,
I would like to hear opinions of the best way to include files (classes) within each other, without getting previously defined errors. Anyone have good tips for doing this?

[IanWright]

Hi,
I would like to hear opinions of the best way to include files (classes) within each other, without getting previously defined errors. Anyone have good tips for doing this?

Everything I have read suggests using defines like:

[CODE=cpp]#ifndef MyClass
#define MyClass

class MyClass
{

}
#endif MyClass[/CODE]

That way you ensure it only ever gets included just once

[weaknessforcats]

Yes and no.

When you #ifndef MyClass, you are banking on MyClass being a unique name. If it's not and is already defined from some other include, then this header won't be included at all.

You need to #ifndef a unique symbol.

The most commonly used thing is a variation on the include file name. Since all headers included in a single build have to have unique names, you can use the header file name. I usually see things like:

[code=cpp]
//MyClass.h

#ifndef _MYCLASSH_
#define _MYCLASSH_

//etc...

#endif
[/code]

The underscores are meant to separate your symbols from the user application symbols.

If you are packaging each class in its own header file and .cpp file, then you have a reasonable convention.