How to define function pointer

This is a discussion on How to define function pointer within the C Programming forums, part of the General Programming Boards category; Look: I write codes in file DLL(name dll1.dll), Code: extern "C" _declspec(dllexport) int __stdcall ret() { return 100; } and ...

  1. #1
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    How to define function pointer

    Look:
    I write codes in file DLL(name dll1.dll),
    Code:
    extern "C" _declspec(dllexport) int __stdcall ret()
    {
            return 100;
    }
    and then I want to use this function:
    Code:
    typedef int (__stdcall FUN)();
            FUN *fun=NULL;
    
            HMODULE hmod=LoadLibrary("dll1.dll");
            if(NULL==hmod)
            {
                    printf("error load\n");
                    return -1;
            }
            fun=(FUN*)GetProcAddress(hmod,"ret");
            if(NULL==fun)
            {
                    printf("error GetProcAddress:%d\n",GetLastError());
                    return -1;
            }
    but error number of function GetProcAddress is 127,
    I want to know How to correct?

  2. #2
    and the hat of wrongness Salem's Avatar
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    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  3. #3
    Registered User whiteflags's Avatar
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    GetProcAddress Function (Windows)
    Return Value

    If the function succeeds, the return value is the address of the exported function or variable.
    return 100; is meaningless anyway.

  4. #4
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    Quote Originally Posted by leetow2003 View Post
    but error number of function GetProcAddress is 127,
    I want to know How to correct?
    System Error Codes (0-499) (Windows)
    Quote Originally Posted by MSDN
    ERROR_PROC_NOT_FOUND
    127 (0x7F)
    The specified procedure could not be found.
    Use the right export name. (hint: dumpbin /exports)

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    You might also want to check that you are loading the right library. The names "dll1.dll" and "dlll.dll" look a lot alike in code (one reason why some style guides actively discourage using names containing the letter l and the digit 1). If you are loading a wrong dll, it will probably not export the function you want to call.
    Right 98% of the time, and don't care about the other 3%.

  6. #6
    and the Hat of Guessing tabstop's Avatar
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    While we're talking about error messages, OP should look at FormatMessage Function (Windows)

  7. #7
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    Quote Originally Posted by leetow2003 View Post
    Look:
    I write codes in file DLL(name dll1.dll),
    Code:
    extern "C" _declspec(dllexport) int __stdcall ret()
    {
            return 100;
    }
    and then I want to use this function:
    Code:
    typedef int (__stdcall FUN)();
            FUN *fun=NULL;
    
            HMODULE hmod=LoadLibrary("dll1.dll");
            if(NULL==hmod)
            {
                    printf("error load\n");
                    return -1;
            }
            fun=(FUN*)GetProcAddress(hmod,"ret");
            if(NULL==fun)
            {
                    printf("error GetProcAddress:%d\n",GetLastError());
                    return -1;
            }
    but error number of function GetProcAddress is 127,
    I want to know How to correct?
    First read this... Dynamic-Link Libraries (Windows) ... yes, ALL of it.

    Now create a proper DLL entry point with DLLMain().
    Export your functions using DLLEXPORT tags.
    Write an include file (.h) for the DLL's functions using DLLIMPORT tags.
    Compile the DLL as a separate project.

    Include the DLL's .h file in your main code.
    Call LoadLibrary() and check it's return value to be sure it loaded.
    Use your functions just like they were local in your .c file.

    You do not need GetProcAddress() to use functions in Windows DLLs.
    Last edited by CommonTater; 08-19-2011 at 08:12 AM.

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