Structure in header won't declare.

This is a discussion on Structure in header won't declare. within the C++ Programming forums, part of the General Programming Boards category; I'm trying to create a game for my own entertainement, and for some reason, it gives me an error. I'm ...

  1. #1
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    Structure in header won't declare.

    I'm trying to create a game for my own entertainement, and for some reason, it gives me an error.

    I'm posting the entire thing so far.

    Main.cpp
    Code:
    //Inculde the main header file
    #include "main.h"
    //Incude the global variable allocation header
    #include "globalvar.h"
    
    //Game initialization function. Gets the game ready to run.
    int functMainStartGame()
    {
        global.exitgame = false;
    }
    
    //Step function, for the main program. All main program code executed here.
    int functMainStep()
    {
        //while(global.exitgame == false)
        //{
        ////put code for game here.
        //}
        
    }
    
    //Game ending function. Ends classes, closes rendering system, ect.
    int functMainEndGame()
    {
    }
    
    int main()
          {
          functMainStartGame();
          functMainStep();
          functMainEndGame();
          return 0;
          }
    main.h
    Code:
    //todo: Add header files to declare here.
    
    //create global variable container.
    
    struct globalStruct
    {
          int exitgame;
          int *entities[0];
          int numbofentities;
    };
    extern globalStruct global;//declare it


    And globalvar.h
    Code:
    globalStruct global;
    EDIT: Oh, entites.cpp too.
    Code:
    #include "globalvar.h"
    
    class entMain
    {
          public:
                int myx;
                int myy;
                float xspeed;
                float yspeed;
          entMain(int x, int y)
          {
          global.instances[global.numbofentities] = &this;
          global.numbofentities += 1;
          }
          ~entMain()
          {
          }
          int entRepeatMe()
          {
          }
    };
    http://img170.imageshack.us/img170/9614/whatdk4.png

    I'm,using Dev C++ v4.9.9.2.

    Please note I am just beginning at C++, so it may have been something simple.

    Thanks

    -CornJer

  2. #2
    Frequently Quite Prolix dwks's Avatar
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    It helps to post the exact error and the line on which it occured; however, I can guess from your title what the error is.

    What's this supposed to do? Is it just a template?
    Code:
    int *entities[0];
    Are you getting a linker error to the effect that you have two variables of the same name?
    dwk

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  4. #4
    Frequently Quite Prolix dwks's Avatar
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    Well, entries.cpp includes globalvar.h but not main.h; it tries to declare a globalStruct without knowing what a globalStruct is. You need to have the definition of the structure in entries.cpp.

    [edit]
    Think about it; after the preprocessor does its job, entries.cpp looks like this:
    Code:
    // What's a globalStruct?
    globalStruct global; // was #include "globalvar.h"
    
    class entMain
    {
          public:
    You were very thourough in your question, by the way. I'm impressed.
    [/edit]
    Last edited by dwks; 10-21-2006 at 10:28 PM.
    dwk

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    Thanks!

    But now it gives me this error as well:

    http://img135.imageshack.us/img135/1672/error2rk2.png

  6. #6
    Frequently Quite Prolix dwks's Avatar
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    globalStruct doesn't appear to have an instances member; perhaps you meant entities?
    dwk

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  7. #7
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    Code:
          global.instances[global.numbofentities] = &this;
    That line... first: global has no member named instances. The closest thing is probably entities. Second, (the error) is that you are saying "&this" - take the address of 'this'. (I cannot imagine what the answer would be, can you?) The variable 'this' is a pointer to the class who's member is being called, and is (in this case) of type entMain *.
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    Yeah, sorry, meant entities.

    So if the keyword "this" doesn't point to an instance of class's address, what does?

  9. #9
    Frequently Quite Prolix dwks's Avatar
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    It does point to the instance of a class; but it's a pointer already. &this will give you **class_type.
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
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    Odd. If thats so, why does it give me this error?

    Code:
    global.entities[global.numbofentities] = this;
    http://img100.imageshack.us/img100/760/error3ti9.png

    Sorry to keep pestering you.

  11. #11
    Frequently Quite Prolix dwks's Avatar
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    You're trying to assign a class to an
    Code:
    int *entities[0];
    Not good. Declare it like so:
    Code:
    entMain *entities[whatever];
    You may need a forward declaration before the structure:
    Code:
    class entMain;
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
    "Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
    "The only real mistake is the one from which we learn nothing." -- John Powell


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    Excellent! It runs perfectly now!

    Thanks a bundle!

  13. #13
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    As a note, making an array of pointers to objects is not very good practice, for 2 reasons:

    1. No way to automatically deallocate the objects,
    2. No way to automatically allocate/deallocate the array.

    I'd say you should consider a boost:tr_vector<> for this job. It will automatically call destructors for your objects as they're removed, and it will automatically call destructors when your program ends.
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  14. #14
    and the hat of int overfl Salem's Avatar
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    You do know you can copy and paste errors from dev-c++, you don't have to keep posting images.
    Just select the "Compile Log" tab and you can just select the text.
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