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++.

Daniel Frederico Lins Leite · Accepted Answer · 2019-09-07 15:45:03Z

11

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 if (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

More:
Using Messages and Message Queues
https://learn.microsoft.com/en-us/windows/win32/winmsg/using-messages-and-message-queues

edited Sep 7, 2019 at 15:45

Daniel Frederico Lins Leite

1,3349 silver badges13 bronze badges

answered Mar 14, 2010 at 7:25

John Knoeller

34.3k4 gold badges66 silver badges93 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Tom J Nowell Over a year ago

The problem here is that although I would now have code that runs key up and key down, I also have code that is not portable. I would need a way of converting WPARAM into something more portable, instead of taking all my crossplatform code and making it windows only so that I can test for virtual key values, hence 'char' being used. I also don't want to spend a day writtng code for every character to convert

Torbilicious · Accepted Answer · 2014-07-03 11:58:09Z

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))
{
    switch (mssg.message)
    {
        case WM_QUIT:
            PostQuitMessage (0);
            notdone = false;
            quit = true;
            break;

        case WM_KEYDOWN:
            WPARAM param = mssg.wParam;
            char c = MapVirtualKey (param, MAPVK_VK_TO_CHAR);
            this->p->Input ()->Keyboard ()->Listeners ()->OnKeyDown (c);
            break;

        case WM_KEYUP:
            WPARAM param = mssg.wParam;
            char c = MapVirtualKey (param, MAPVK_VK_TO_CHAR);
            this->p->Input ()->Keyboard ()->Listeners ()->OnKeyUp (c);
            break;
    }
    // dispatch the message
    TranslateMessage (&mssg);
    DispatchMessage (&mssg);
}

Collectives™ on Stack Overflow

Keyboard Input & the Win32 message loop

2 Answers 2

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related