How do I prevent a Win32 application from running in the background after the main window is closed?

Question

I'm a beginner to the Win32 API, but I am intermediately experienced with C++. For learning purposes, I created, according to references, tutorials, and examples, a very simple Win32 application.

The problem is, after the main window is closed, its process still runs in the background. How can I prevent this? In my WndProc function, I do have a WM_DESTROY case with DestroyWindow, but it doesn't seem to be doing the trick. The code is below:

#include <cstdio>
#include <cstdlib>

#ifdef UNICODE
#include <tchar.h>
#endif

#include <Windows.h>

HINSTANCE hinst;
HWND hwnd;

LRESULT CALLBACK WndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);

#ifdef UNICODE
int WINAPI _tWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPTSTR lpCmdLine, int nCmdShow)
#else
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
#endif
{
    MSG msg;
    WNDCLASSEX mainclass;
    BOOL bRet;
    UNREFERENCED_PARAMETER(lpCmdLine);

    mainclass.cbSize =          sizeof(WNDCLASSEX);
    mainclass.style =           CS_VREDRAW | CS_HREDRAW;
    mainclass.lpfnWndProc =     (WNDPROC) WndProc;
    mainclass.cbClsExtra =      NULL;
    mainclass.cbWndExtra =      NULL;
    mainclass.hInstance =       hInstance;
    mainclass.hIcon =           NULL;
    mainclass.hCursor =         LoadCursor(NULL, IDC_ARROW);
    mainclass.hbrBackground =   (HBRUSH) COLOR_WINDOW;
    mainclass.lpszMenuName =    NULL;
    mainclass.lpszClassName =   TEXT("MainWindowClass");
    mainclass.hIconSm =         NULL;

    if (!RegisterClassEx(&mainclass))
        return FALSE;

    hinst = hInstance;

    hwnd = CreateWindowEx(
        WS_EX_WINDOWEDGE,
        TEXT("MainWindowClass"),
        TEXT("Test Window"),
        WS_CAPTION | WS_VISIBLE | WS_SIZEBOX | WS_SYSMENU | WS_MINIMIZEBOX | WS_MAXIMIZEBOX,
        CW_USEDEFAULT,
        CW_USEDEFAULT,
        CW_USEDEFAULT,
        CW_USEDEFAULT,
        NULL,
        NULL,
        hinst,
        NULL);

    ShowWindow(hwnd, nCmdShow);
    UpdateWindow(hwnd);

    while ((bRet = GetMessage(&msg, NULL, 0, 0)) != 0)
    {
        if (bRet != -1)
        {
            TranslateMessage(&msg);
            DispatchMessage(&msg);
        }
    }
    return (int) msg.wParam;
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    PAINTSTRUCT ps;
    switch(uMsg)
    {
    case WM_DESTROY:
        DestroyWindow(hwnd);
        break;
    case WM_PAINT:
        BeginPaint(hwnd, &ps);
        EndPaint(hwnd, &ps);
        break;
    default:
        return DefWindowProc(hwnd, uMsg, wParam, lParam);
    }
    return 0;
}

Answer 1

Don't call DestroyWindow(). The message is telling you that your window has already been destroyed. Call PostQuitMessage(0) to quit the application.