SetWindowLongPtrA callback function

Question

I want to use the Windows API to get keyboard input from a window. From what I have heard, I can create a callback function that will be called when some events happen. I just don't know how.

ModuleManager::ModuleManager() {
    HWND getGameWindow = FindWindow(NULL, TEXT("GameName"));
    wndProc = (WNDPROC)SetWindowLongPtrA(getGameWindow, GWLP_WNDPROC, 0);
}

LRESULT CALLBACK ModuleManager::WndProc(const HWND hwnd, unsigned int message, uintptr_t wParam, long lparam) {
    if (message == WM_CHAR) {
        for (Module* m : modules) {
            if (m->getKeybinding() == wParam) {
                m->isActive = !m->isActive; // toggle
            }
        }
    }

    return CallWindowProcA(wndProc, hwnd, message, wParam, lparam);
}

Here is my current code. I want to set a callback on WndProc function.

This is not how you subclass a control. See [Subclassing Controls](https://learn.microsoft.com/en-us/windows/win32/controls/subclassing-overview). — IInspectable, Mar 06 '22 at 18:43
If you have resolved your issue please [mark](https://meta.stackexchange.com/a/5235) it as accepted — Junjie Zhu - MSFT, Mar 11 '22 at 09:09

score 0 · Accepted Answer · answered Mar 06 '22 at 18:32

It seems i figured it out. The callback function must be a static function for some reason. So the correct code is following:

ModuleManager::ModuleManager() {
    HWND getGameWindow = FindWindow(NULL, TEXT("GameName"));
    wndProc = (WNDPROC)SetWindowLongPtrA(getGameWindow, GWLP_WNDPROC, (LONG_PTR) &ModuleManager::WndProc);
}

LRESULT CALLBACK ModuleManager::WndProc(const HWND hwnd, unsigned int message, uintptr_t wParam, long lparam) {
    if (message == WM_CHAR) {
        for (Module* m : modules) {
            if (m->getKeybinding() == wParam) {
                m->isActive = !m->isActive; // toggle
            }
        }
    }

    return CallWindowProcA(wndProc, hwnd, message, wParam, lparam);
}

read here also https://stackoverflow.com/questions/31648180/c-changing-hwnd-window-procedure-in-runtime — Sven Nilsson, Mar 06 '22 at 18:34

SetWindowLongPtrA callback function

1 Answers1