Class files including other classes

This is a discussion on Class files including other classes within the C++ Programming forums, part of the General Programming Boards category; Hiya, got a bit of a problem with some of my classes. Each class has its own files (such as ...

  1. #1
    Registered User combatdave's Avatar
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    Class files including other classes

    Hiya, got a bit of a problem with some of my classes. Each class has its own files (such as MyClass.cpp and MyClass.h), and all is going swimmingly.

    My code is designed such that there is a class, AppClass, which contains all instances of the other classes - AgentClass and ItemClass. Inside my AgentClass, i need a function to which i can pass my instance of AppClass, as each AgentClass object will need to search for nearby Agents or Items. Below is exactly which files include which other files.


    (ObjectClass is the base class on which all objects inside the game (be it items or agents) are built upon.)


    Main.cpp:
    Code:
    #include "ObjectClass.h"
    #include "AgentClass.h"
    #include "ItemClass.h"
    #include "AppClass.h"

    AppClass.h:
    Code:
    #include "ObjectClass.h"
    #include "AgentClass.h"
    #include "ItemClass.h"
    AgentClass.h:
    Code:
    #include "ObjectClass.h"
    ItemClass.h:
    Code:
    #include "ObjectClass.h"
    Now, inside my AgentClass i have tried including AppClass.h in order to let me use an AppClass instance as a parameter for a function. The problem is, including AppClass throws up a stupid amount of errors, none of which even hint at how to remedy the problem.

    Any ideas? even ideas of what to google would be appreciated - i have tried already but its quite a hard problem to phrase in such a way that google understands.

    Cheers for your time.
    ( )

  2. #2
    Code Goddess Prelude's Avatar
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    >Any ideas?
    Are you using inclusion guards? Do you have global data? There are a lot of things that can go wrong with this, though inclusion guards and namespaces can clear up most of them.
    My best code is written with the delete key.

  3. #3
    Registered User combatdave's Avatar
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    im going to guess no to inclusion guards, not entirely sure what they are...

    i do have a small amount of global data, but that is held inside the main.cpp file, and nowhere else

    cheers for the speedy reply
    ( )

  4. #4
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    >> inside my AgentClass i have tried including AppClass.h
    If you meant AgentClass.h there, you will likely need to use forward declarations instead of including the AppClass header directly. Since AppClass.h already includes AgentClass.h, you cannot have AgentClass.h include AppClass.h, it becomes a circular include.

    When you only need to include a header because a type is used as a function parameter, or as a pointer or reference member in the class, you should use a forward declaration instead of including the entire header. This is true in general, and required when you have circular includes.

  5. #5
    Code Goddess Prelude's Avatar
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    >im going to guess no to inclusion guards, not entirely sure what they are...
    Inclusion guards are just a preprocessor trick that makes sure the contents of a header are only included once, regardless of how deeply you nest them. It's a good idea for every header you make:
    Code:
    #ifndef SOMEUNIQUENAME
    #define SOMEUNIQUENAME
    
    // Your header stuff here
    
    #endif
    My best code is written with the delete key.

  6. #6
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    Generally people use the name of the file as part of the SOMEUNIQUENAME part. So you might use APPCLASS_H for your AppClass.h file.

  7. #7
    Registered User combatdave's Avatar
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    ah yes, i am already using inclusion guards.

    il give the forward declaration gubbins a go shortly. if i understand correctly, its as simple as putting "class AppClass;" in?

    cheers.
    ( )

  8. #8
    Registered User
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    >> its as simple as putting "class AppClass;" in?
    Yes, and of course removing the #include "AppClass.h". You will need to #include "AppClass.h" in the cpp file, though, which you probably should have been doing anyway.

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