Thread: Making a (atom) class in a (struct) class makes big errors!

A while ago I tried to create some functions that would automaticly handle classes and their windows for me. But the program would crash when I called CreateWindow(), I found that the problem was dealing with the class. But how so I am unsure of. Now I tried to make another one like it from scratch. Again, the same problem. Does anyone know why the class isn't working with the window? Code below.

Code:

// Script by Yarin Licht.
// Made September, 2007.

#include <windows.h>
#include <commctrl.h>

struct POD {
   WNDCLASSEX wincl;
   int nWide, nHigh;
   // Got rid of a line
   char* pszMenu;
   HWND hwnd;
   MSG msg;
};

HANDLE NewApp(HINSTANCE hInst, char *pszClass, char *pszMenu, WNDPROC wndproc)
{
   POD *poda = new POD[1];
   poda[0].hwnd = NULL;
   ZeroMemory(&poda[0].wincl, sizeof(WNDCLASSEX));
   poda[0].wincl.hInstance = hInst;
   poda[0].wincl.lpszClassName = pszClass;
   poda[0].wincl.lpfnWndProc = wndproc;
   poda[0].wincl.style = CS_DBLCLKS;
   poda[0].wincl.cbSize = sizeof(WNDCLASSEX);
   poda[0].wincl.hIcon = LoadIcon(NULL, IDI_APPLICATION);
   poda[0].wincl.hIconSm = LoadIcon(NULL, IDI_APPLICATION);
   poda[0].wincl.hCursor = LoadCursor(NULL, IDC_ARROW);
   poda[0].wincl.lpszMenuName = pszMenu;
   poda[0].wincl.cbClsExtra = 0;
   poda[0].wincl.cbWndExtra = 0;
   poda[0].wincl.hbrBackground = (HBRUSH)COLOR_3DSHADOW;
   if(!RegisterClassEx(&poda[0].wincl)) return NULL;
   return (HANDLE)poda;
}

#define pod (((POD*)hPod)[0])

int MakeApp(HANDLE hPod, char *pszTitle, int nWide, int nHigh)
{
   int WINDOW_WIDTH = nWide, WINDOW_HEIGHT = nHigh;
   WINDOW_WIDTH += GetSystemMetrics(SM_CXFIXEDFRAME) * 2;
   WINDOW_HEIGHT += GetSystemMetrics(SM_CXFIXEDFRAME) + GetSystemMetrics(SM_CYCAPTION);
   if(pod.wincl.lpszMenuName) WINDOW_HEIGHT += GetSystemMetrics(SM_CYMENU);
   pod.hwnd = CreateWindowEx(WS_EX_CONTROLPARENT, pod.wincl.pszClassName, pszTitle,
                             WS_OVERLAPPEDWINDOW &~WS_THICKFRAME &~WS_MAXIMIZEBOX,
                             (GetSystemMetrics(SM_CXSCREEN)/2) - (WINDOW_WIDTH/2),
                             (GetSystemMetrics(SM_CYSCREEN)/2) - (WINDOW_HEIGHT/2),
                             WINDOW_WIDTH, WINDOW_HEIGHT, 0, 0, pod.wincl.hInstance, 0);
   if(!pod.hwnd) return FALSE;
   ShowWindow(pod.hwnd, SW_SHOWNORMAL);
   return TRUE;
}

WPARAM RunApp(HANDLE hPod)
{
   while(GetMessage(&pod.msg, NULL, 0, 0)) {
      TranslateMessage(&pod.msg);
      if(pod.msg.message == WM_DESTROY) break;
      DispatchMessage(&pod.msg);   }
   return pod.msg.wParam;
}

void FreeApp(HANDLE hPod)
{
   if(pod.hwnd) SendMessage(pod.hwnd, WM_DESTROY, 0, 0);
   UnregisterClass(pod.wincl.pszClassName, pod.wincl.hInstance);
   delete [ ](POD*)hPod;
   return;
}

// End of script file.

LRESULT CALLBACK WindowProcedure(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
   switch(message)
   {
      case WM_DESTROY:
      {
         PostQuitMessage(0);
         break;
      }
      default:
         return DefWindowProc(hwnd, message, wParam, lParam);
    }
    return TRUE;
}

int WINAPI WinMain(HINSTANCE hThis, HINSTANCE hPrevInst, LPSTR lpszArgs, int nShow)
{
   HANDLE hApp = NULL;
   hApp = NewApp(hThis, "TestClass", NULL, WindowProcedure);
   MakeApp(hApp, "Test App", 300, 300);
   RunApp(hApp);
   FreeApp(hApp);
   return TRUE;
}

// End of script file.

From first glance, I see that pod.pszClass is used without being initialized. (i.e. NewApp() does not allocate memory for pod.pszClass, but MakeApp() expects it to point to something valid.)

p.s. your macro "pod" is bound to cause some confusion with local var "pod" as well..

Not 100% but I think the WNDPROC has to be a 'static' method.

This relates to how the class stores links to methods (function pointers) without scope (ie uses WndProc rather than the correct this->WinProc or MyClass::WinProc). That is WIN32 does not support (.NET) delegates.