Linker Errors

This is a discussion on Linker Errors within the C++ Programming forums, part of the General Programming Boards category; --> x already defined in y.obj I've just about had it with this problem. How the hell do I fix ...

  1. #1
    Registered User The Dog's Avatar
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    Linker Errors

    --> x already defined in y.obj

    I've just about had it with this problem. How the hell do I fix this?

    I have a main.h file with all function defs, globals, macros etc.

    Then I have many .cpp files which include main.h.

    I took this type of file layout from CDX's code, and problem is, their code links, mine doesn't.

    There's virtually no difference between their code, and mine, in terms of file layout.

    I'm using VS .NET

  2. #2
    and the hat of wrongness Salem's Avatar
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    > x already defined in y.obj
    Means x is defined in a header file, and not merely declared in a header file (given your descriptions of the project)

    Or x is truly defined in two places by mistake
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  3. #3
    Registered User major_small's Avatar
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    Re: Linker Errors

    Originally posted by The Dog
    Then I have many .cpp files which include main.h.
    did you try doing this:
    Code:
    #ifndef _MAIN_H
    #define _MAIN_H
    
    //main.h goes in here
    
    #endif //_MAIN_H
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  4. #4
    Registered User The Dog's Avatar
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    Even with include guards I get the errors.

    Let's say my main.h looks like this:
    Code:
    #include <windows.h>
    #include <stdio.h>
    #include <vector>
    
    using std::vector;
    
    //Define macros here
    #define PI  3.141592654
    //End Define macros
    
    //Globals here
    #ifdef MAIN_CPP
       #define DECLARE
    #else
       #define DECLARE extern
    #endif
    
    DECLARE int globalVariable;
    DECLARE char globalString;
    //End Globals
    
    //All function prototyes
    int WINAPI WinMain(...);
    LRESULT CALLBACK WndProc(...);
    
    int function();
    void function_2();
    //End Function Prototypes
    Now, in main.cpp, i'll have something like this:
    Code:
    #define MAIN_CPP
    #include "main.h"
    
    int WINAPI WinMain(...)
    {
    }
    
    LRESULT CALLBACK WndProc(...)
    {
    }
    Then I have about six other .cpp files which include main.h


    One other thing:
    If project A was originally built with VS 6, and project B is originally built with VS .NET, would there be any difference between the two projects if the VS 6 project was converted to a VS .NET project?

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