undefined identifier GWL_USERDATA

[Jim Gadrow]

Ok, I'm trying to create a windows application and I am experiencing an error when storing and retrieving a pointer from a window long.

I receive the 'Error: undefined identifier GWL_USERDATA' message when compiling unless I add:

extern (Windows) int GWL_USERDATA;

The program compiles correctly. However, when I attempt to restore the object from the long (pointer) my application terminates. I checked and the value of GWL_USERDATA is equal to 0 (the default int value). Thus, the program is NOT storing the pointer in the correct location. I think 0 actually corresponds to the GWL_EXSTYLE does it not?

Here's a modified version of winsamp.d that illustrates the error:

/* Compile with:
 *	dmd winsamp gdi32.lib winsamp.def
 */

import std.c.windows.windows;
import std.c.stdio;

const int IDC_BTNCLICK = 101;
const int IDC_BTNDONTCLICK = 102;

class control
{
	void Paint () {}
}

extern (Windows)
{
	uint GetWindowLongA (HWND hWnd, int nIndex);
	uint SetWindowLongA (HWND hWnd, int nIndex, LONG dwNewLong);
	int GWL_USERDATA;
}

T WinGetLong (T) (HWND hWnd, int which = GWL_USERDATA)
{
	return cast (T) GetWindowLongA (hWnd, which);
}

void WinSetLong (T) (HWND hWnd, T value, int which = GWL_USERDATA)
{
	SetWindowLongA (hWnd, which, cast (long) value);
}

extern(Windows)
int WindowProc(HWND hWnd, uint uMsg, WPARAM wParam, LPARAM lParam)
{
	switch (uMsg)
	{
		control pCtrl = cast (control) WinGetLong!(control*) (hWnd);
		
		case WM_CREATE:
			control Ctrl = new control ();
			WinSetLong!(control*) (hWnd, &Ctrl);
			break;
		
		
	    case WM_COMMAND:
	    {
		switch (LOWORD(wParam))
		{
		    case IDC_BTNCLICK:
			if (HIWORD(wParam) == BN_CLICKED)
				MessageBoxA(hWnd, "Hello, world!", "Greeting",
					MB_OK | MB_ICONINFORMATION);
			break;
		    case IDC_BTNDONTCLICK:
			if (HIWORD(wParam) == BN_CLICKED)
			{
			    MessageBoxA(hWnd, "You've been warned...", "Prepare to GP fault",
				    MB_OK | MB_ICONEXCLAMATION);
			    *(cast(int*) null) = 666;
			}
			break;
		}
		break;
	    }

	    case WM_PAINT:
	    {
		pCtrl.Paint ();
		static char[] text = "D Does Windows";
		PAINTSTRUCT ps;
		HDC dc = BeginPaint(hWnd, &ps);		
		RECT r;
		GetClientRect(hWnd, &r);
		HFONT font = CreateFontA(80, 0, 0, 0, FW_EXTRABOLD, FALSE, FALSE,
			FALSE, ANSI_CHARSET, OUT_DEFAULT_PRECIS, CLIP_DEFAULT_PRECIS,
			DEFAULT_QUALITY, DEFAULT_PITCH | FF_DONTCARE, "Arial");
		HGDIOBJ old = SelectObject(dc, cast(HGDIOBJ) font);
		SetTextAlign(dc, TA_CENTER | TA_BASELINE);
		TextOutA(dc, r.right / 2, r.bottom / 2, text.ptr, text.length);
		SelectObject(dc, old);
		EndPaint(hWnd, &ps);
		break;
	    }
	    case WM_DESTROY:
		PostQuitMessage(0);
		break;

	    default:
		break;
	}
	return DefWindowProcA(hWnd, uMsg, wParam, lParam);
}

int doit()
{
	HINSTANCE hInst = GetModuleHandleA(null);
	WNDCLASS wc;
	wc.lpszClassName = "DWndClass";
	wc.style = CS_OWNDC | CS_HREDRAW | CS_VREDRAW;
	wc.lpfnWndProc = &WindowProc;
	wc.hInstance = hInst;
	wc.hIcon = LoadIconA(cast(HINSTANCE) null, IDI_APPLICATION);
	wc.hCursor = LoadCursorA(cast(HINSTANCE) null, IDC_CROSS);
	wc.hbrBackground = cast(HBRUSH) (COLOR_WINDOW + 1);
	wc.lpszMenuName = null;
	wc.cbClsExtra = wc.cbWndExtra = 0;
	auto a = RegisterClassA(&wc);
	assert(a);
	
	HWND hWnd, btnClick, btnDontClick;
	hWnd = CreateWindowA("DWndClass", "Just a window", WS_THICKFRAME |
		WS_MAXIMIZEBOX | WS_MINIMIZEBOX | WS_SYSMENU | WS_VISIBLE,
		CW_USEDEFAULT, CW_USEDEFAULT, 400, 300, HWND_DESKTOP,
		cast(HMENU) null, hInst, null);
	assert(hWnd);
	
	btnClick = CreateWindowA("BUTTON", "Click Me", WS_CHILD | WS_VISIBLE,
		0, 0, 100, 25, hWnd, cast(HMENU) IDC_BTNCLICK, hInst, null);

	btnDontClick = CreateWindowA("BUTTON", "DON'T CLICK!", WS_CHILD | WS_VISIBLE,
		110, 0, 100, 25, hWnd, cast(HMENU) IDC_BTNDONTCLICK, hInst, null);

	MSG msg;
	while (GetMessageA(&msg, cast(HWND) null, 0, 0))
	{
		TranslateMessage(&msg);
		DispatchMessageA(&msg);
	}
	
	return 1;
}

/**********************************************************/

/* Note the similarity of this code to the console D startup
 * code in \dmd\src\phobos\dmain2.d
 * You'll also need a .def file with at least the following in it:
 *	EXETYPE NT
 *	SUBSYSTEM WINDOWS
 */

extern (C) void gc_init();
extern (C) void gc_term();
extern (C) void _minit();
extern (C) void _moduleCtor();
extern (C) void _moduleUnitTests();

extern (Windows)
int WinMain(HINSTANCE hInstance,
	HINSTANCE hPrevInstance,
	LPSTR lpCmdLine,
	int nCmdShow)
{
    int result;

    gc_init();			// initialize garbage collector
    _minit();			// initialize module constructor table

    try
    {
	_moduleCtor();		// call module constructors
	_moduleUnitTests();	// run unit tests (optional)

	result = doit();	// insert user code here
    }

    catch (Object o)		// catch any uncaught exceptions
    {
	MessageBoxA(null, cast(char *)o.toString(), "Error",
		    MB_OK | MB_ICONEXCLAMATION);
	result = 0;		// failed
    }

    gc_term();			// run finalizers; terminate garbage collector
    return result;
}