Windows Programming, window not opening, no build errors - c++

Question

I don't have much experience with windows programming, but can't specifically see what's wrong with this code, yet the window doesn't open. Although sometimes, not always, it will be open in task manager, so my guess is that it is registering the class and creating the window, but the problem is with the ShowWindow() function. But, I'm not positive.
To my understanding the flow of the program is:
Window is created with the registered class.
The window is shown.
Continuously looks for messages that are processed in the window Proc.
I feel like I've done all these things, so is my understanding wrong, or is my code missing something?
Thanks.
Source Code:
#include <Windows.h>
LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
if (uMsg == WM_DESTROY)
{
PostQuitMessage(0);
return 0;
}
DefWindowProc(hwnd, uMsg, wParam, lParam);
}
int WINAPI wWinMain(HINSTANCE hinstance, HINSTANCE hPrevInstance, LPWSTR lpCmdLine, int nCmdShow)
{
//Variable for message loop.
MSG msg;
//Setting up the window class.
WNDCLASSEX windowClass;
windowClass.cbSize = sizeof(windowClass);
windowClass.style = CS_HREDRAW | CS_VREDRAW | CS_PARENTDC;
windowClass.lpfnWndProc = WindowProc;
windowClass.hInstance = hinstance;
windowClass.hbrBackground = (HBRUSH)COLOR_WINDOW;
windowClass.lpszClassName = "WindowClass";
RegisterClassEx(&windowClass);
HWND windowHandle = CreateWindowEx(WS_EX_OVERLAPPEDWINDOW, "WindowClass", "My Program", WS_OVERLAPPEDWINDOW, 500, 200, 800, 500, NULL, NULL, hinstance, 0);
if (!windowHandle)
return FALSE;
ShowWindow(windowHandle, nCmdShow);
// Start the message loop.
while (GetMessage(&msg, NULL, 0, 0) != 0)
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
// Return the exit code to the system.
return msg.wParam;
}

Answer 1

Your window procedure is invoking DefWindowProc but not actually returning the result, and you have undefined behavior because of that. The return value is important, and it can control how the OS handles successive messages to your window. For example, it's important to return the correct value in response to the WM_CREATE message.
Change your window procedure to:
LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
if (uMsg == WM_DESTROY)
{
PostQuitMessage(0);
return 0;
}
return DefWindowProc(hwnd, uMsg, wParam, lParam);
}
Also, as Mark Ransom identified in the comments section, you should zero-initialize your WNDCLASSEX structure to ensure that you don't get garbage on any members that you didn't explicitly initialize.