c++dllloadlibrarygetprocaddress

GetProcAddress function in C++

Hello guys: I've loaded my DLL in my project but whenever I use the GetProcAddress function. it returns NULL! what should I do? I use this function ( double GetNumber(double x) ) in "MYDLL.dll"

Here is a code which I used:

typedef double (*LPGETNUMBER)(double Nbr);
HINSTANCE hDLL = NULL;
LPGETNUMBER lpGetNumber;
hDLL = LoadLibrary(L"MYDLL.DLL");
lpGetNumber = (LPGETNUMBER)GetProcAddress((HMODULE)hDLL, "GetNumber");
Solution

  • Checking return codes and calling GetLastError() will set you free. You should be checking return codes twice here. You are actually checking return codes zero times.

    hDLL = LoadLibrary(L"MYDLL.DLL");

    Check hDLL. Is it NULL? If so, call GetLastError() to find out why. It may be as simple as "File Not Found".

    lpGetNumber = (LPGETNUMBER)GetProcAddress((HMODULE)hDLL, "GetNumber");

    If lpGetNumber is NULL, call GetLastError(). It will tell you why the proc address could not be found. There are a few likely scenarios:

    1. There is no exported function named GetNumber
    2. There is an exported function named GetNumber, but it is not marked extern "c", resulting in name mangling.
    3. hDLL isn't a valid library handle.

    If it turns out to be #1 above, you need to export the functions by decorating the declaration with __declspec(dllexport) like this:

    MyFile.h

    __declspec(dllexport) int GetNumber();

    If it turns out to be #2 above, you need to do this:

    extern "C"
{
  __declspec(dllexport) int GetNumber();
};