Getting a "multiple definition of <classname>" error.

This is a discussion on Getting a "multiple definition of <classname>" error. within the C++ Programming forums, part of the General Programming Boards category; I have a file that includes another class and when I try to make an object of that class I ...

  1. #1
    Ethernal Noob
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    Getting a "multiple definition of <classname>" error.

    I have a file that includes another class and when I try to make an object of that class I get the error "multiple definition of..." and the name of that class. Why am I getting these errors. I have header guards and there is only one instance of the class, so why do I get multiple definition errors.

  2. #2
    Kiss the monkey. CodeMonkey's Avatar
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    Who knows. Let's see the code.
    "If you tell the truth, you don't have to remember anything"
    -Mark Twain

  3. #3
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    Code:
    #ifndef SCENES_H_INCLUDED
    #define SCENES_H_INCLUDED
    
    #include <GL/glew.h>
    #include <GL/CTargaImage.h>
    #include "TerragenFile.h"
    
    namespace Box
    {
        void setupBoxScene();
        void renderBox();
    }
    
    
    namespace Terrain
    {
        TerragenFile ter;
        bool setupTerrain();
        void renderTerrain();
    }
    
    #endif // SCENES_H_INCLUDED
    Code:
    #include "scenes.h"
    void Terrain::renderTerrain()
    {
    
    }
    
    bool Terrain::setupTerrain()
    {
        return true;
    }
    I haven't even implemented it and it gives me this. Plus the error points to some file called "locale_facets.tcc"

  4. #4
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    I solved it by moving the instantiation of the class into the cpp file. I need to brush up a little on the namespace a little, I was using it on instinct and examples.

  5. #5
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by indigo0086 View Post
    I solved it by moving the instantiation of the class into the cpp file. I need to brush up a little on the namespace a little, I was using it on instinct and examples.
    The only things you should EVER put in a header file are DECLARATIONS. You can declare a class, but don't instantiate it. As you have discovered

    So, question: why did you do it that way in the first place? Do you want the "ter" object to be accessible from multiple source files? Then you should declare it as "extern." And some (one, and only one) source file should define it as a real variable.

  6. #6
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    I thought namespace had "classlike" functioality, have a namespace have a 'member' so to speak. Now I get why it can't be that way. I was just green with namespaces. I'll use extern.

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