exporting c++ dll to c# winform

Question

I have these in my c++ header file

#ifndef S2dll_H
#define S2dll_H

#ifdef S2dll_EXPORTS
#define S2dll_API __declspec(dllexport)

#else
    #pragma message("automatic link to S2dll.LIB")
    #pragma comment(lib, "S2dll.lib")
#define S2dll_API __declspec(dllimport)
#endif

class is declared like this

class S2dll_API Sample
{
//members here
}

a cpp file containing function definitions, constructors

void * __stdcall CreateS() //constructor
{
    return new SDLL;
}


void __stdcall DestroyS(void * objPtr) //destructor
{
   s* sObj = (s *) objPtr;
    if (sobj)
        delete sObj;
}

exporting/exposing this function

void __stdcall setvaluesDLL(void *ptr, int x, int y,int s, int p)
    {


        Sample *dll =  (Sample *) ptr;

        if (dll)
        {
            dll->setposition(c); //functions in the cpp file
            dll->setlocation(x,y);
            dll->setsize(s);
        }

    }

a .def file

LIBRARY BS2dll

EXPORTS
CreateS
DestroyS
setvaluesDLL

so I am trying to access it in my c# win form

made this to expose it

static internal  class dllcall
{
[DllImport(@"adrress\S2dll.dll", CallingConvention = CallingConvention.StdCall)]
    public static extern void setvaluesDLL(IntPtr ptr,int x, int y, int s, int p);
}

calling it in my winform

private void Assign_Click(object sender, EventArgs e)
{
dllcall.setvaluesDLL(ptr, x, y, s, p);//all values are int
 }

I get this error: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.

been searching google and staring at this code for hours and every time I manage to solve a problem, a new one comes out whenever I call setvaluesDLL(//parameters)

EDITED: IntPtr ptr is my main problem here and I have absolutely no idea how to use nor initialize it

Answer 1

You have to initialize first setvaluesDLL parameter value with CreateS() result. This method should be imported from the dll too. The same as DestroyS - to release memory properly