C / C++ / MFC

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//a normal function I call from the main application:
extern "C" __declspec(dllexport) void funcA(const unsigned long long a, const unsigned long long b);
//following function should be the callback, triggering an assigned function in the main application
extern "C"
{
    typedef void(__stdcall* callback_t)(unsigned int halfbeast);

    __declspec(dllexport) void public_func_taking_callback(callback_t evHnd)
    {
        evHnd(333);//value just for testing
    }
}


void funcA(
    const unsigned long long a,
    const unsigned long long b)
{
    //some code here... do things with a and b
   if(a>10)                       //trigger the event in the main application
       callback_t(public_func_taking_callback);   
}

typedef void (__stdcall *eventCallback)(unsigned int miau);
typedef void (__stdcall *setCallback)(eventCallback evHnd);
void __stdcall CallB(unsigned int);

//---------------------------------------------------------------------------
void __fastcall TForm1::Button1Click(TObject *Sender)
{
signed int retval;
unsigned int i;
char txt[7];
unsigned long long a,index;
UnicodeString USt;
HINSTANCE dllHandle=NULL;

//Obtain a handle to the DLL
dllHandle = LoadLibrary(L"test.dll");
if (!dllHandle){
    ShowMessage("Could not load test.dll");
    Form1->Close();
    }
else{    //Lib was loaded, try to get data
    void (__stdcall* funcA)(const unsigned long long a, const unsigned long long b);  
    funcA=(void(__stdcall*)(const unsigned long long a, const unsigned long long b))GetProcAddress(dllHandle,"funcA");

    // DLL function pointer
    setCallback values=(setCallback)GetProcAddress(dllHandle, "public_func_taking_callback");
    if(values != NULL){
        values(&CallB);
        }

    if(!funcA){
        Memo1->Text="No handle to function found.";
        }
    else{
        funcA(1,1);
        funcA(100,100);
        }
    FreeLibrary(dllHandle);
    }

}
//---------------------------------------------------------------------------
void __stdcall CallB(unsigned int halfbeast){
ShowMessage("triggered");
}
//---------------------------------------------------------------------------