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Include loops

Started by Taile Nov 17, 2001 at 5:52 PM 2 replies 350+ views

Original Post

Nov 17, 2001 at 5:52 PM

I am writing an upgradable encapsulation of everything. Don''t ask why. I guess I am a bit obsessive, or maybe I have a complex. Who knows? Well, anyway, I have one class called clsUniverse in clsUniverse.h and .cpp. Another class called clsObject is in clsObject.h and .cpp. clsObject can be stripped down to this: class clsObject { public: friend clsUniverse; //I hope this is legal - tell me private: bool exists; clsUniverse* the_universe; //the one that it "exists" in } clsUniverse can be stripped down to this: class clsUniverse { public: void Create (clsObject& an_object); // an_object.the_universe = this; } the clsObject.h file needs to include clsUniverse.h, but clsUniverse.h needs to include clsObject.h. That would mean they would keep including each other infinitely. How do I overcome this problem? I could do something like this: clsUniverse.h- #include "clsObject.h" clsObject.h- #ifndef _CLSUNIVERSE_H_ #include "clsUniverse.h" #endif Is there any other solution?

S1CA

169

S1CA

Nov 17, 2001 at 6:40 PM

#pragma once

Although the method of defining a variable to mark inclusion of the header file is the most common (and compiler independent).

BTW a small aside if you are using the #define method, don''t put any underscore at the front of the symbol you''re using. Symbols which begin with underscores followed by a capital letter are reserved by both the C and C++ standards for compiler and SDK use. If you use names with underscores, don''t complain if you ever get a namespace conflict.

--
Simon O''''Connor
Creative Asylum Ltd
www.creative-asylum.com

Oluseyi

526

Oluseyi

Nov 17, 2001 at 6:42 PM

Forward declarations.

In clsObject.h (btw are you a VB programmer?):

class clsUniverse; // this is a forward declaration

class clsObject
{
  ...
};

And then in clsUniverse.h:

class clsObject;
class clsUniverse
{
  ...
};

The downside to forward declarations is that you cannot reference any properties (data members) or operations (methods) of the class. The name is essnetially declareed as a placeholder.

Fruny

203

Fruny

Nov 17, 2001 at 9:37 PM

So long as it is only a complex, you are doing fine. The day it becomes a quaternion, seek medical advice.

Each of your header file should be structured that way :

  
#ifndef HEADER_FILE_H
#define HEADER_FILE_H

.
.
.

#endif /* HEADER_FILE_H */

Since your whole header file is bracketed by the #ifndef/#endif statements, any #include statement beyond the first will only add whitespaces to the file being processed.

Or, as Oluseyi said, if you only need to declare pointers/references/arguments, you can use a forward declaration.

The problem with #pragma is that they are compiler-specific.

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