Using Call Back Function C# delegate dll in C++

Question

but i have a error how can't i fix it?

this is my c# Code

 public delegate void Callback_Calc(int nResult);
    [Guid("180726E3-7185-4224-BF27-3A7A60E5D1A7")]
    public interface ICal
    {
        int Add(int a, int b);
        void Add_Callback(int a,int b,IntPtr Callback_Result);
    }
    [Guid("9FF07EDD-8DEE-4CCA-9BDF-2C753F7717AC")]
    public class Calc : ICal
    {
        public int Add(int a, int b)
        {
            return (a + b);
        }
        public void Add_Callback(int a, int b, IntPtr Callback_Result)
        {
            int sum = a + b;
            Callback_Calc func = (Callback_Calc)Marshal.GetDelegateForFunctionPointer(Callback_Result, typeof(Callback_Calc));
            func(sum);
        }
    }

this is my C++ Code

 
extern "C" void __stdcall callback_func(int nResult);
void __fastcall TForm2::btn2Click(TObject *Sender)
{
 ICal *m_Calc;
    HRESULT hr = CoInitialize(NULL);
    hr =  CoCreateInstance(CLSID_Calc,NULL,CLSCTX_INPROC_SERVER,IID_ICal,reinterpret_cast<void**>(&m_Calc));
    if(FAILED(hr))
    {
     CoInitialize(NULL);
    }
    int a = m_Calc->Add(2,5);
    lbl1->Caption = a;
    m_Calc->Add_Callback(10,10,(_Callback_Calc *)callback_func);
 CoInitialize();
}
extern "C" void __stdcall callback_func(int nResult)
{
 int a = nResult;
    int b = nResult;
}

this is my C++ error Code

[C++ Error] ComputAddTest.cpp(55): E2034 Cannot convert '_Callback_Calc *' to 'long' [C++ Error] ComputAddTest.cpp(55): E2342 Type mismatch in parameter 'Callback_Result' (wanted 'long', got '_Callback_Calc *') [C++ Error] ComputAddTest.cpp(56): E2193 Too few parameters in call to '__stdcall CoInitialize(void *)'

thank you

Tanner H. · Accepted Answer · 2019-03-20 01:27:23Z

1

Your Add_Callback function requires a pointer to the function. So in the line:

m_Calc->Add_Callback(10,10,(_Callback_Calc *)callback_func);

you need to change the 3rd parameter to a pointer to callback_func.

answered Mar 20, 2019 at 1:27

Tanner H.

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