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:

#ifndef MyClass
#define MyClass
 
class MyClass
{
 
}
#endif MyClass

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:

//MyClass.h
 
#ifndef  _MYCLASSH_
#define _MYCLASSH_
 
//etc...
 
#endif
 

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.