Keyboard Input & the Win32 message loop

Question

How do I handle key presses and key up events in the windows message loop? I need to be able to call two functions OnKeyUp(char c); and OnKeyDown(char c);.

Current literature I've found from googling has lead me to confusion over WM_CHAR or WM_KEYUP and WM_KEYDOWN, and is normally targeted at PDA or Managed code, whereas I'm using C++.

Answer 1

A typical C++ message loop looks like this

MSG msg;
while (GetMessage(&msg, null, 0, 0))
{
    TranslateMessage(&msg);
    DispatchMessage(&msg);
}

The function of TranslateMessage is to generate WM_CHAR messages from WM_KEYDOWN messages, so if you want to see WM_CHAR messages you need to be sure to pass WM_KEYDOWN messages to it. If you don't care about WM_CHAR messages, you can skip that, and do something like this.

extern void OnKeyDown(WPARAM key);
extern void OnKeyUp(WPARAM key);

MSG msg;
while (GetMessage(&msg, null, 0, 0))
{
    if (msg.message == WM_KEYDOWN)
       OnKeyDown (msg.wParam);
    else (msg.message == WM_KEYUP)
       OnKeyUp(msg.wParam);
    else
    {
       TranslateMessage(&msg);
       DispatchMessage(&msg);
    }
}

Notice that OnKeyDown and OnKeyUp messages are defined as taking a WPARAM rather than a char. That's because the values for WM_KEYDOWN and WM_KEYUP aren't limited to values that fit in a char. See WM_KEYDOWN

Answer 2

Use char c = MapVirtualKey(param,MAPVK_VK_TO_CHAR); to convert virtual key codes to char, and process WM_KEYUP and WM_KEYDOWN and their wParams.

if (PeekMessage( &mssg, hwnd, 0, 0, PM_REMOVE)) {
    if(mssg.message == WM_QUIT){
        PostQuitMessage(0);
        notdone = false;
        quit = true;
    } else if(mssg.message == WM_KEYDOWN){
        WPARAM param = mssg.wParam;
        char c = MapVirtualKey(param,MAPVK_VK_TO_CHAR);
        this->p->Input()->Keyboard()->Listeners()->OnKeyDown(c);
        continue;
    } else if(mssg.message == WM_KEYUP){
        WPARAM param = mssg.wParam;
        char c = MapVirtualKey(param,MAPVK_VK_TO_CHAR);
        this->p->Input()->Keyboard()->Listeners()->OnKeyUp(c);
        continue;
    }
    // dispatch the message
    TranslateMessage(&mssg);
    DispatchMessage(&mssg);
}