Need help with plug-ins

This is a discussion on Need help with plug-ins within the Windows Programming forums, part of the Platform Specific Boards category; I am designing a plug-in interface for a program. I can get the driver program to load the plug-in but ...

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    Need help with plug-ins

    I am designing a plug-in interface for a program. I can get the driver program to load the plug-in but when I try to access a function the function pointer value is NULL. I've gotten this to work using extern "C" but that will not do for this application because polymorphism will be used extensively. I know it is possible to do plug-ins with a C++ interface but I don't know how and thus far the internet has been less than useful.

    I've also tried to access the functions via their mangled names but that didn't work either.

    I am using Microsoft Visual C++ 6.0 and am using the LoadLibrary fuction to load a plug-in and GetProcAddress to get the pointers of functions.

    Thanks

  2. #2
    and the hat of wrongness Salem's Avatar
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    How do you call GetProcAddress?

    C++ names are mangled when you compile them, to help resolve parameter overloading. You need to be looking for the mangled name (I think).

    Moved to windows board.
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    Quote Originally Posted by Salem
    How do you call GetProcAddress?

    C++ names are mangled when you compile them, to help resolve parameter overloading. You need to be looking for the mangled name (I think).

    Moved to windows board.
    well, it depends on the interface of the function. For a function with no parameters i use
    int (*func)(void) = (int(*)(void))GetProcAddress(hm,"FunctionName");
    where hm is the handle to the plug-in.

    I have tried using the mangled names. I'm not sure if I used them correctly. I just ran dumpbin on the dll with the /export option and copied and pasted the name.

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    You probably didn't use the correct mangled name. What is the prototype of the function you are trying to call?

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    the function is: int TestPlugin::Type()

    dumpbin tells me the name is ?Type@TestPlugin@@EAEHXZ

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    What compiler are you using? Are you exporting the function?

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    Quote Originally Posted by bithub
    What compiler are you using? Are you exporting the function?
    I'm using Microsoft Visual Studio 6.0 and yes, I am exporting the function. If I wasn't I don't think dumpbin would list it as an exported function.

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    Ok, you can't just export a function that is part of a class, then call it. You should export the entire class. This way you can create class objects, and call the function that way. Visual Studio will create a .lib file when you compile the dll class. Just have your application link to that .lib file, and then you include the dll header file. Once you've done that, you can create the class, and call its functions.

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    I don't think linking to the lib file will be possible. It needs to support future plug-ins. But I will look into exporting the entire class. Thanks

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    I see what you are trying to do now. Read the following article:
    http://www.codeguru.com/Cpp/W-P/win32/article.php/c1443

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    Wonderful, that looks to be exactly what I need. I'll give it a try tomorrow and let you know how it goes.

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