Why is GetMessage exiting my program without sending any message? - c++

Question

here is my problem. I'm trying to create a windowless program that still uses trayIcon and Hooks, so I need to use messages (or not?) but when I use them, I don't know how to free my memory when I kill my process. Even classes's destructors aren't called. Here is a test main:
int WINAPI WinMain(HINSTANCE hInst, HINSTANCE hPrev, LPSTR pCmdLine, int nCmdShow)
{
MSG msg;
OutputDebugStringW(L"Start.\n");
while (GetMessageW(&msg, NULL, NULL, NULL) > 0)
{
OutputDebugStringW(L"one.\n");
TranslateMessage(&msg);
OutputDebugStringW(L"two.\n");
DispatchMessage(&msg);
OutputDebugStringW(L"three.\n");
}
OutputDebugStringW(L"end.\n");
return 0;
}
As I saw in the doc, the GetMessage() call should return 0 or less to exit, but when I run it, and then shut it down, I get only the "Start." log, and I don't understand why. And if there is no way to get through this loop, then how can i call my destructors? I do have a window for my trayIcon that doesn't receive any message, maybe i should pass it as parameter to GetMessage()?
PS: my project uses trayIcons and Hooks, and when I run it with the same debug prints, it display once the 4 first strings, but nothing at shutdown, not even the "end." string.
EDIT: my (terrible) trayIcon creation:
LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
OutputDebugStringW(L"Message!\n");
switch (uMsg)
{
case WM_DESTROY:
OutputDebugStringW(L"Close message received\n");
PostQuitMessage(0);
return 0;
case WM_PAINT:
{
PAINTSTRUCT ps;
HDC hdc = BeginPaint(hwnd, &ps);
FillRect(hdc, &ps.rcPaint, (HBRUSH)(COLOR_WINDOW + 1));
EndPaint(hwnd, &ps);
}
case WM_RBUTTONUP:
{
OutputDebugStringW(L"Trying to open Context menu\n");
POINT const pt = { LOWORD(wParam), HIWORD(wParam) };
break;
}
return 0;
}
return DefWindowProc(hwnd, uMsg, wParam, lParam);
}
bool CreateNotifyIcon(HINSTANCE& hInstance)
{
NOTIFYICONDATA notif = {};
static const wchar_t class_name[] = L"ExtendClass";
WNDCLASSEX wx = {};
wx.cbSize = sizeof(WNDCLASSEX);
wx.lpfnWndProc = WindowProc;
wx.hInstance = hInstance;
wx.lpszClassName = class_name;
RegisterClassEx(&wx);
HWND win = CreateWindowEx(0, class_name, L"Windows Extend", WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, NULL, NULL, hInstance, NULL);
if (win == NULL)
OutputDebugStringW(L"failed to create window\n");
ZeroMemory(&notif, sizeof(NOTIFYICONDATA));
notif.cbSize = sizeof(NOTIFYICONDATA);
notif.uFlags = NIF_ICON | NIF_MESSAGE | NIF_TIP;
// Need to find a non-busy uID
notif.uID = 44421;
notif.hWnd = win;
StringCchCopy(notif.szTip, ARRAYSIZE(notif.szTip), L"Access Windows Extend options.");
StringCchCopy(notif.szInfo, ARRAYSIZE(notif.szInfo), L"Access Windows Extend options.");
StringCchCopy(notif.szInfoTitle, ARRAYSIZE(notif.szInfoTitle), L"Windows Extend");
notif.hIcon = (HICON)LoadImage(NULL, L"./Luma.ico", IMAGE_ICON, 0, 0, LR_LOADFROMFILE | LR_DEFAULTSIZE);
if (!Shell_NotifyIcon(NIM_ADD, &notif))
{
OutputDebugStringW(L"failed to create notifIcon\n");
return false;
}
return true;
}

Answer 1

GetMessage() does not return until it receives a window/thread message, or has a message to synthesis. In the code you have shown, you are not creating any windows, not posting any thread messages to yourself, and not creating any hooks that require a message loop, so there is nothing for GetMessage() to do. It is blocked indefinitely. That is why you are only seeing your start message and nothing else happens until you forcibly kill the program.
Since you intend to display a system tray icon, you need a window for it, even if just a hidden window, in order to receive notifications about user interaction with the icon. Your GetMessage() loop will handle messages for all windows created in the same thread as the loop, since you are setting the hWnd parameter to NULL instead of a specific window. Once you create your tray icon window, the loop will receive messages for it just fine. You can then provide your tray icon with a popup menu that contains an item that will exit your message loop when clicked, thus allowing you to exit from WinMain() gracefully, invoke destructors, etc.

Answer 2

GetMessage returns -1 if an error occurs. So you should do while != 0 generally. But if you are not seeing "end", then your application is probably crashing.
https://msdn.microsoft.com/en-us/library/windows/desktop/ms644936(v=vs.85).aspx