Thread: API basics

I understand that there is:

Code:

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)

which is the main function for the window.

Then there is:

Code:

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)

which does the main processing for the window and that the WinMain function calls this function in the "DispatchMessage(&Msg);" call but how do I create a variable in the main function so that it can be accessed in the WndProc function?

In WinMain() use the window handle and post your self a message using PostMessage(), then process the message in WndProc(). The following code shows the basic structure.

Code:

#define WM_MY_MESSAGE1 WM_USER +1
#define WM_MY_MESSAGE2 WM_USER +2
#define WM_MY_MESSAGE3 WM_USER +3
struct My_Struct_A
{
     int a;     int b;     int c;
};

int APIENTRY WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    ...
     ...
     hWnd = CreateWindow(...); 
     ...
     ...
     char strHello[] = "hello";
     PostMessage( hWnd, WM_MY_MESSAGE1 ,0, (LPARAM )strHello );

     int iValue = 12345; 
     PostMessage( hWnd, WM_MY_MESSAGE2 ,0, (LPARAM )iValue );

     struct My_Struct_A *pMySA = (struct My_Struct_A *) malloc(sizeof(struct My_Struct_A));
     ...
     pMySA->a = 1234;
     ...
     PostMessage( hWnd, WM_MY_MESSAGE2 ,0, (LPARAM )pMySA );

     // Main message loop:
     while (GetMessage(&msg, NULL, 0, 0)) 
     {
          if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg)) 
          {
               TranslateMessage(&msg);
               DispatchMessage(&msg);
          }
     }

     return msg.wParam;
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
     ...
     ...
     int iNumber;
     char *strText;
     struct My_Struct_A *pMySA;

     switch (message) 
     {
          case WM_MY_MESSAGE1:
               strText = (char*) lParam;
               break;

          case WM_MY_MESSAGE2:
               iNumber = (int) lParam;
               break;

          case WM_MY_MESSAGE3:
               pMySA = (struct My_Struct_A *) lParam;
               break;
               ...
               ...
               ...
               ...

          default:
               return DefWindowProc(hWnd, message, wParam, lParam);
   }
   return 0;
}

Thanks heaps Scarlet7. That did the trick. Why are structures used? I have done some c programming but have done mostly c++ and java. Why don't u use classes?