I am writing a C# application which uses Interop services to access functions in a native C++ DLL. I am already using about 10 different functions which are working.
Now I am not sure how to handle passing a callback as a parameter so that the DLL can call my code.
Here is the function prototype of the DLL:
typedef void (WINAPI * lpfnFunc)(const char *arg1, const char *arg2)
And the function that allows me to pass the above type:
int WINAPI SetFunc(lpfnFunc f)
Here is my C# code for the delegate and function definitions:
public delegate void Func(string arg1, string arg2);
public static void MyFunc(string arg1, string arg2)
Here is my C# code for the SetFunc Interop function:
[DllImport("lib.dll", CharSet = CharSet.Ansi)]
public static extern int SetFunc(Func lpfn);
And finally here is the code where I call the SetFunc function and pass it my callback:
SetFunc(new Func(MyFunc));
Unfortunately my function is not being called when it should be. The return value of the SetFunc function is returning the error code for a Success, so either it's not calling my function or it's not working because my code is wrong.
This works for me:
Calc.h (Calc.dll, C++):
extern "C" __declspec(dllexport) double Calc(double x, double y, double __stdcall p(double, double));
Calc.cpp (Calc.dll, C++):
#include "calc.h"
__declspec(dllimport) double Calc(double x, double y, double __stdcall p(double, double))
{
double s = p(x*x, y*y);
return x * y + s;
}
Program.cs (Sample.exe, C#):
class Program
{
delegate double MyCallback(double x, double y);
[DllImport("Calc.dll", CallingConvention = CallingConvention.Cdecl)]
static extern double Calc(double x, double y, [MarshalAs(UnmanagedType.FunctionPtr)]MyCallback func);
static void Main(string[] args)
{
double z = Calc(1, 2, (x, y) => 45);
}
}