Windows API wont quit - c++

Question

For some reason after I close this window my program wont exit and goes into an infinite loop. The solution to this problem seems to be changing GetMessage(&message, handel, 0, 0) to GetMessage(&message, NULL, 0, 0). However I don't understand why this is. Can somebody please explain. Also I don't see why I call UpdateWindow(handel) since the window will show without it.
#include <iostream>
#include <Windows.h>
using namespace std;
LRESULT CALLBACK EventHandler(HWND, UINT, WPARAM, LPARAM);
int WINAPI WinMain(HINSTANCE inst, HINSTANCE prev, PSTR args, int cmd)
{
MSG message;
HWND handel;
WNDCLASS win_class;
win_class.style = CS_HREDRAW | CS_VREDRAW;
win_class.cbClsExtra = 0;
win_class.cbWndExtra = 0;
win_class.lpszClassName = "Window";
win_class.hInstance = inst;
win_class.hbrBackground = GetSysColorBrush(COLOR_3DDKSHADOW);
win_class.lpszMenuName = NULL;
win_class.lpfnWndProc = EventHandler;
win_class.hCursor = LoadCursor(NULL, IDC_ARROW);
win_class.hIcon = LoadIcon(NULL, IDI_APPLICATION);
RegisterClass(&win_class);
handel = CreateWindow(win_class.lpszClassName, "Window", WS_OVERLAPPEDWINDOW | WS_VISIBLE, 100, 100, 350, 250, NULL, NULL, inst, NULL);
ShowWindow(handel, cmd);
UpdateWindow(handel);
//Loop does not end.
while(GetMessage(&message, handel, 0, 0))
{
cout << "LOOP" << endl;
DispatchMessage(&message);
}
return WM_QUIT;
}
LRESULT CALLBACK EventHandler(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
static long long count = 0;
count++;
cout << "CALL #" << count << endl;
if(msg == WM_DESTROY)
{
PostQuitMessage(0);
return 0;
}
return DefWindowProc(hwnd, msg, wParam, lParam);
}

Answer 1

WM_QUIT is not sent to any window, just placed in the thread's message queue with no HWND, that's why it doesn't match your filter.

Answer 2

Take a look at GetMessage and PostQuitMessage in MSDN
If the parameter hWnd of GetMessage function is NULL, GetMessage retrieves messages for any window that belongs to the current thread, and any messages on the current thread's message queue whose hwnd value is NULL.
The PostQuitMessage function posts a WM_QUIT message to the thread's message queue, not to the current window.

Answer 3

Here's a good opportunity to exercise your "search-the-MSDN-documentation" abilities:
First, let's look up the documentation for WM_QUIT:
Indicates a request to terminate an application, and is generated when
the application calls the PostQuitMessage function. This message
causes the GetMessage function to return zero.
...
The WM_QUIT message is not associated with a window and therefore will
never be received through a window's window procedure. It is retrieved
only by the GetMessage or PeekMessage functions.
Then, let's look up the documentation for GetMessage():
Retrieves a message from the calling thread's message queue. The
function dispatches incoming sent messages until a posted message is
available for retrieval.
...
hWnd [in, optional] Type: HWND
A handle to the window whose messages are to be retrieved. The window
must belong to the current thread.
If hWnd is NULL, GetMessage retrieves messages for any window that
belongs to the current thread, and any messages on the current
thread's message queue whose hwnd value is NULL (see the MSG
structure). Therefore if hWnd is NULL, both window messages and thread
messages are processed.
Therefore, you want to use NULL as the window handle for GetMessage(), not handel, since WM_QUIT is not associated with any window.
There's plenty more information about how Windows programs typically handle messages also from MSDN.
As the side note, the message for window close events is WM_CLOSE, which in turn causes your window to be destroyed by default. WM_DESTROY means your window is already on it's way to being destroyed. So if you want to intercept the close event (say to ask your user to save any changes), you would handle the WM_CLOSE event.
Also, as shown in the GetMessage() documentation, you should actually have your GetMessage() loop look like this:
BOOL bRet;
while( (bRet = GetMessage( &msg, hWnd, 0, 0 )) != 0)
{
if (bRet == -1)
{
// handle the error and possibly exit
}
else
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
Because GetMessage() can actually return 1, 0, or -1 (despite it returning a BOOL).