inline function declaration

This is a discussion on inline function declaration within the C++ Programming forums, part of the General Programming Boards category; Hi, just a quick question. I'm running MSVC, and in my code, I have a header called CGeom.h: Code: #ifndef ...

  1. #1
    Carnivore ('-'v) Hunter2's Avatar
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    Arrow inline function declaration

    Hi, just a quick question. I'm running MSVC, and in my code, I have a header called CGeom.h:
    Code:
    #ifndef (...)
    #define (...)
    
    inline float degreesToRadians(float degrees);
    
    #endif
    In CGeom.cpp, I have the function definition for degreesToRadians:
    Code:
    inline float degreesToRadians(float degrees)
    {
         //do something
         return (result);
    }
    When I compiled this with the debug settings, it worked fine; under Release build, I got a unresolved external symbol for degreesToRadians. The problem went away when I just merged the definition and prototype(?) together in the header, instead of having them separate.

    Can anybody tell me why this happens?
    Just Google It. √

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  2. #2
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    inline functions in C++ have internal linkage. You need to put the definition in the declaration in the .h file. A common way to do this is by putting all of your class declarations in the header and then at the end of the header putting #include "math.inl" and have all of your inline code in there. This isn't standard or anything but a lot of people do it. Hope this clears it up.
    "...the results are undefined, and we all know what "undefined" means: it means it works during development, it works during testing, and it blows up in your most important customers' faces." --Scott Meyers

  3. #3
    Carnivore ('-'v) Hunter2's Avatar
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    Thanks MrWizard, my confusion is no more
    Just Google It. √

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  4. #4
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    Originally posted by MrWizard
    inline functions in C++ have internal linkage.
    No,
    7.1.2 Function Specifiers,Footnote 79
    The inline keyword has no effect on the linkage of a function.
    So they have the linkage they'd if inline was not specified. Linkage is always defined, the three choices are internal, external, or no linkage. An inline function with no explicit linkage spec has external linkage.

  5. #5
    Carnivore ('-'v) Hunter2's Avatar
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    Oh, great. So what's the problem then?
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  6. #6
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    Well the new C++ standard says it has no effect. The old C++ standard says it has internal linkage. Guess which standard the old compilers go by.
    "...the results are undefined, and we all know what "undefined" means: it means it works during development, it works during testing, and it blows up in your most important customers' faces." --Scott Meyers

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