Templates from DLL or static library problem

This is a discussion on Templates from DLL or static library problem within the C++ Programming forums, part of the General Programming Boards category; Hi, I was trying to store a templated function in a DLL to use it in some other app, but ...

  1. #1
    Registered User mikahell's Avatar
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    Templates from DLL or static library problem

    Hi, I was trying to store a templated function in a DLL to use it in some other app, but after
    getting linker errors, I figured out that we can't put templates in DLL because the function
    doesn't compile itself in the DLL, some says it's only a pattern to tell how to create new
    functions, or so I heard...

    While I was googling, I saw that even if templates on DLLs don't work, it should be possible
    to achieve it with static libs files only, no DLL... So I made a test in a static library, but I still
    got linker error. I though that static libs would simply work as if it was hidden uncompiled code. So... is there any way to have externally used templates with libs?

    Code:
    //Lib project source
    template <class X>
    void TestFunc(X var)
    {
    	//Deal with var
    }
    
    //Test application
    #pragma comment(lib, "Test.lib")
    int main(void)
    {
    	TestFunc<int>(123);
    	return 0;
    }

  2. #2
    Algorithm Dissector iMalc's Avatar
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    In short, you can't go as far as you want to. The best option is to just leave the template implementation in header files, and include that in each project.

    You can abstract out the common parts between the different types and put that in a lib, and then have template functions make use of the lib.
    For example, this is much the same as if one were to implement say std::sort for a vector by implementing a template wrapper function that uses C's qsort.
    I believe there is an STL implemention out there that does that kind of thing and claims to reduce code bloat somewhat. Can't remember the details though.
    In general it wont be able to be optimised as well.

    You other option is to force it to compile a template instantiation for each type of interest, by actually using the functions for each type in the lib, and then I believe they can be exported. That wont then work for other types though, of course.
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  3. #3
    Registered User mikahell's Avatar
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    Ok, I get it. Then I will just leave them in header files with the code. Thanks for your help!

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