Creating class - linker problems

This is a discussion on Creating class - linker problems within the C++ Programming forums, part of the General Programming Boards category; Should this work? Code: /* .h */ class cPlayer //declaration { public: float x, y, z; cPlayer(); //constructor }; cPlayer::cPlayer(); ...

  1. #1
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    Creating class - linker problems

    Should this work?

    Code:
    /* .h */
    
    class cPlayer	 		//declaration
    {
    	public:
    		float x, y, z;
    
    		cPlayer(); 	//constructor
    
    };
    
    cPlayer::cPlayer(); 		//construct
    
    void do_something(cPlayer);
    
    /* .cpp */
    
    cPlayer player; 		//instance
    
    player.x=10;			//assignment
    
    main()
    {
    	do_something(player)	//pass
    }
    
    /* other.cpp - includes same .h */
    
    
    void do_something(cPlayer &player)
    {
    	player->y=20;		//use by reference
    
    }
    Last edited by alanb; 09-03-2009 at 07:26 AM. Reason: Change call to pass instance

  2. #2
    Guest Sebastiani's Avatar
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    The linker can't find the constructor because you've only declared, but not defined, it.

    Also, main returns an int.

    EDIT:

    One more thing. Your declaration for do_something doesn't match it's definition, either.
    Last edited by Sebastiani; 09-03-2009 at 07:31 AM.

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    Quote Originally Posted by Sebastiani View Post
    The linker can't find the constructor because you've only declared, but not defined, it.
    I tried duplicating the declaration just after it and removed the constructor and gave the floats a value. The compiler says - 'cPlayer' : 'class' type redefinition.
    Also, main returns an int.
    I was paraphrasing, sorry.
    One more thing. Your declaration for do_something doesn't match it's definition, either.
    Should the declaration indicate a pointer to cPlayer rather than to a type cPlayer?

  4. #4
    Guest Sebastiani's Avatar
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    >> I tried duplicating the declaration just after it and removed the constructor and gave the floats a value. The compiler says - 'cPlayer' : 'class' type redefinition.

    You don't need to duplicate or remove anything - simply define a body for the constructor *somewhere*.

    >> Should the declaration indicate a pointer to cPlayer rather than to a type cPlayer?

    The declaration indicates that the parameter is to be a temporary (eg: copy of the value passed in), whereas the definition specifies a reference. You need to pick one and stick with it (probably the latter, since you seem to need to make changes to the object).

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    Quote Originally Posted by Sebastiani View Post
    The declaration indicates that the parameter is to be a temporary (eg: copy of the value passed in), whereas the definition specifies a reference. You need to pick one and stick with it (probably the latter, since you seem to need to make changes to the object).
    void do_something(cPlayer &player); //declaration

  6. #6
    Guest Sebastiani's Avatar
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    That's it.

    I'm assuming you fixed the undefined reference to the constructor, as well, then?

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    I began by removing it until I could compile cleanly, then I took the assignments collecting in the main .cpp and put them back into a constructor and all seems well.

  8. #8
    Registered User hk_mp5kpdw's Avatar
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    Code:
    /* .cpp */
    
    cPlayer player; 		//instance
    
    player.x=10;			//assignment
    
    main()
    {
    	do_something(player)	//pass
    }
    Does that assignment work for you? It shouldn't... or is this more "paraphrasing"?
    "Owners of dogs will have noticed that, if you provide them with food and water and shelter and affection, they will think you are god. Whereas owners of cats are compelled to realize that, if you provide them with food and water and shelter and affection, they draw the conclusion that they are gods."
    -Christopher Hitchens

  9. #9
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    No, I wasn't, and I've moved that line (and others like it) to a constructor within the declaration, and I removed the instance names in the process. I can now access the members in that way from within the functions that the class is passed to by reference.

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