Variables in header files

This is a discussion on Variables in header files within the C++ Programming forums, part of the General Programming Boards category; My project consists of two source files and one header file. DX.cpp Code: #include "stdafx.h" //... case WM_LBUTTONDOWN: i+=0.1; break; ...

  1. #1
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    Variables in header files

    My project consists of two source files and one header file.

    DX.cpp
    Code:
    #include "stdafx.h"
    //...
    case WM_LBUTTONDOWN:
                         i+=0.1;
                         break;
    //...
    graphics.cpp
    Code:
    #include "stdafx.h"
    //...
    D3DXMatrixRotationX(&matRotateX, i);
    //...
    stdafx.h
    Code:
    //...
    float i;
    //...
    The problem is that i need stdafx.h to be included in each of my source files, but that redefines i. Where should I put variables which I need in every souce file?

  2. #2
    Code Goddess Prelude's Avatar
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    >Where should I put variables which I need in every souce file?
    You can put the declarations for a variable in your header, but the definition should be placed in the implementation file:
    Code:
    //...
    extern float i;
    //...
    Code:
    #include "stdafx.h"
    //...
    float i;
    //...
    D3DXMatrixRotationX(&matRotateX, i);
    //...
    Of course, using a global name like i is flirting with disaster because it's such a common identifier. Also, stdafx.h is a well known header in Microsoft compilers, so it's unwise to reuse it.
    My best code is written with the delete key.

  3. #3
    and the hat of wrongness Salem's Avatar
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    > float i;
    // put this in a header file
    extern float i;

    // put this in ONE source file
    float i;

    That is, if you insist on using global variables.

    Meh - beaten by the alphabet again
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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  4. #4
    Reverse Engineer maxorator's Avatar
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    I am wondering, what makes "stdafx.h" so popular header file name?
    "The Internet treats censorship as damage and routes around it." - John Gilmore

  5. #5
    and the hat of wrongness Salem's Avatar
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    > what makes "stdafx.h" so popular header file name?
    It's the name of the file which VC++ uses to implement "precompiled headers".

    You put all the commonly used header files your project needs into stdafx.h
    You then #include "stdafx.h" as the first include in all your source files.

    Supposedly, it speeds up builds.
    I do know one thing though, it is the single biggest PITA as almost every single noob has a question about it at some point.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  6. #6
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    Thanks guys, I can always rely on you. Now help me out with debugging

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