Win32 Inconsistent CreateWindowEx Call - c++

Question

I'm trying to wrap my head around the Win32 API, and when creating the window I get inconsistent results. The call to CreateWindowEx will fail and the result from GetLastError() yields the ERROR_NOT_ENOUGH_MEMORY error code. But sometimes the application successfully creates the window and runs fine. This has left me rather confused.
// Standard Includes
#include <windows.h>
#include <iostream>
#ifndef UNICODE
#define UNICODE
#endif
#ifndef _UNICODE
#define _UNICODE
#endif
#define UNUSED_PARAM(x) (void)(x)
const char szWindowClass[] = "Program";
const char szTitle[] = "Program Desc";
LRESULT CALLBACK WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
int CALLBACK WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
LPSTR lpCmdLine, int nCmdShow) {
UNUSED_PARAM(hPrevInstance);
UNUSED_PARAM(lpCmdLine);
WNDCLASSEX wcex;
HWND hWnd;
wcex.cbSize = sizeof(WNDCLASSEX);
wcex.style = CS_HREDRAW | CS_VREDRAW;
wcex.lpfnWndProc = WndProc;
wcex.cbClsExtra = 0;
wcex.hInstance = hInstance;
wcex.hIcon = LoadIcon(hInstance, IDI_APPLICATION);
wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
wcex.lpszMenuName = NULL;
wcex.lpszClassName = szWindowClass;
wcex.hIconSm = LoadIcon(wcex.hInstance, IDI_APPLICATION);
if(!RegisterClassEx(&wcex)) {
MessageBox(NULL, "Call to RegisterClassEx failed!", szWindowClass, MB_ICONEXCLAMATION | MB_OK);
return 1;
}
hWnd = CreateWindowEx( WS_EX_CLIENTEDGE, // dwExStyle
szWindowClass, // lpClassName
szTitle, // lpWindowName
WS_OVERLAPPEDWINDOW, // dwStyle
CW_USEDEFAULT, CW_USEDEFAULT, // x, y
240, 120, // width, height
NULL, NULL, // hWndParent, hMenu
hInstance, NULL); // hInstance, lpParam
std::cout << GetLastError();
if(hWnd == NULL) {
MessageBox(NULL, "Call to CreateWindow failed!", szWindowClass, MB_ICONEXCLAMATION | MB_OK);
return 1;
}
ShowWindow(hWnd, nCmdShow);
UpdateWindow(hWnd);
// Main message loop
MSG msg;
while (GetMessage(&msg, NULL, 0, 0)) {
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return (int) msg.wParam;
}
LRESULT CALLBACK WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam) {
switch(uMsg) {
case WM_CLOSE:
DestroyWindow(hWnd);
break;
case WM_DESTROY:
PostQuitMessage(0);
break;
default:
return DefWindowProc(hWnd, uMsg, wParam, lParam);
}
return 0;
}

Answer 1

You're not initializing WNDCLASSEX.cbWndExtra which defines how many extra bytes of storage your window class needs.
You should add:
wcex.cbWndExtra = 0;
Before your call to RegisterClassEx. Alternatively you could start with this:
WNDCLASSEX wcex = { sizeof(wcex) };
Which will initialize the cbSize member to the size of the structure and all other members to 0 (or NULL) for you.