Question

So I have a DLL that I made with C++ and I am using it in C#. The problem is that I use a function pointer in C++, so I made a delegate. The hole program works but after it finishes I got a message box stating that the value of ESP was not saved for the function.

My code:
C++ The DLL

typedef void (*FUNCTION_TYPE)(bool);
extern "C"
{
    DLL void prim(int a, FUNCTION_TYPE myF)
    {
        if(a < 2)
        {
            myF(false);
            return;
        }

        for (int i = 2; i < a; i++)
        {
            if (a % i == 0)
            {
                myF(false);
                return;
            }
        }

        myF(true);
    }
};

My C# code (calling the dll):

delegate void SOME_FUNCTION(bool isFine);

        [DllImport("DLLs")]
        private static extern void prim(int n, SOME_FUNCTION afisare);

        static void afisare(bool isFine)
        {
            if (isFine == true)
                Console.WriteLine("Da, e prim");
            else
                Console.WriteLine("Nu, nu e prim");
        }

        static void Main(string[] args)
        {
            SOME_FUNCTION myAfis = afisare;
            prim(17, myAfis);
        }

Answer 1

You have a calling convention mismatch. The C++ function pointer type uses cdecl. The managed code assumes stdcall. Fix it like this:

[UnmanagedFunctionPointer(CallingConvention.Cdecl)]
delegate void SOME_FUNCTION(bool isFine);

Alternatively you could change the calling convention in the C++ code to stdcall:

typedef void (__stdcall *FUNCTION_TYPE)(bool);

But make sure you do only one of these and not both!