Re: CreateWindowEx returns 0, but GetLastError reveals no error

From:

"John Carson" <jcarson_n_o_sp_am_@netspace.net.au>

Newsgroups:

microsoft.public.vc.language

Date:

Tue, 30 Jan 2007 14:33:03 +1100

Message-ID:

<#q0Rk9BRHHA.3412@TK2MSFTNGP02.phx.gbl>

<The.Relinator@gmail.com> wrote in message
news:1170126272.154789.317430@a34g2000cwb.googlegroups.com...

I am new to c++, and I am trying to get my first win32 gui application
to work correctly, however I am experiancing some difficulties. When
creating a window the handle gets passed 0, however when calling
GetLastError, I get the response : 0. The ShowWindow function however
returns ERROR_INVALID_WINDOW_HANDLE. I am stumped as to why this
would happen. Any help would be greatly appreciated. An excerpt is
shown below, and thank you.

WNDCLASSEX wcex;
wcex.cbClsExtra = 0;
wcex.cbSize = sizeof(WNDCLASSEX);
wcex.cbWndExtra = 0;
wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
wcex.hCursor = (HCURSOR)LoadImage(NULL, MAKEINTRESOURCE(OCR_NORMAL),
IMAGE_CURSOR, 0, 0, LR_MONOCHROME | LR_DEFAULTSIZE | LR_SHARED) ;
wcex.hIcon = (HICON)LoadImage(NULL, MAKEINTRESOURCE(OIC_SAMPLE),
IMAGE_ICON, 32, 32, LR_DEFAULTCOLOR | LR_DEFAULTSIZE);
wcex.hIconSm = NULL;
wcex.hInstance = hInstance;
wcex.lpfnWndProc = (WNDPROC)WndProc;
wcex.lpszClassName = L"TestClass";
wcex.lpszMenuName = NULL;
wcex.style = CS_GLOBALCLASS | CS_HREDRAW | CS_VREDRAW;

RegisterClassEx(&wcex);
gHInstance = hInstance;
RECT rect = { 0, 0, 800, 600 };
AdjustWindowRectEx(&rect, WS_OVERLAPPEDWINDOW, FALSE, CS_GLOBALCLASS |
CS_HREDRAW | S_VREDRAW);
gHwnd = CreateWindowEx(WS_EX_LEFT, L"TestClass", L"Test",
WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT, rect.right -
rect.left, rect.bottom - rect.top, HWND_DESKTOP, NULL, hInstance,
NULL);
ShowWindow(gHwnd, nShowCmd);

Aside from the use of various undefined identifiers (which I presume are
defined in your complete code), there is nothing wrong with the code that
you have supplied.

CreateWindowEx does not return until several calls have been made to the
window procedure. Accordingly, the most common reason for CreateWindowEx to
fail is because of a defective window procedure. Try this "vanilla" window
procedure and see if the window is displayed correctly.

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

--
John Carson