cross-referencing #includes
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Thread: cross-referencing #includes

  1. #1
    Join Date
    Jul 2003
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    Durham, England
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    cross-referencing #includes

    This may sound a n00b question, but say I have two files, a.h and b.h. a.h contains a class, a, and b.h contains a class,b. class a has a member of type b, and vice versa for b. How would i arrange the include statements so that it compiles correctly?? thankyou.

  2. #2
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    Include both

  3. #3
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    You can't do this directly. One solution is to use a third header file called defs.h which has forward declarations for the classes. However that presupposes that you are using pointers to classes.

    It *can* also be an indication that your design is bad. In any case, I would look at the design again and ask myself, why I would need to do this.
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  4. #4
    Join Date
    Jan 2004
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    29
    Put a forward declaration in each file, eg

    In a.h
    class b; // forward declaration
    //note do NOT #include "b.h"

    class a
    {
    ...
    b m_b;
    };
    ------------------------------
    In b.h
    #include "a.h"

    class b
    {
    ...
    a m_a;
    };
    -------------------------------
    In the classes, stick to using pointers, otherwise you may find you run into problems, depending on what you're trying to do with the other class.

    You may need to do the forward declaration the other way around, depending on which file your compiler looks at first.

    This may be a sign of bad design, but is frequently inevitable. For example you have to do this to implement the 'visitor pattern' - a famous OO design solution.
    Last edited by JonnoA; February 6th, 2004 at 03:11 PM.

  5. #5
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    KY, USA
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    18,652
    Take a look at the following FAQ...
    Ciao, Andreas

    "Software is like sex, it's better when it's free." - Linus Torvalds


    Article(s): Allocators (STL) Function Objects (STL)

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