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Thread: Alt key virtual codes

  1. #1
    Join Date
    Oct 2017
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    Alt key virtual codes

    Inspecting the `Right Alt` key messages using `Microsoft Spy++` returns the following:
    Code:
    WM_KEYDOWN nVirtKey:VK_CONTROL 
    WM_KEYDOWN nVirtKey:VK_MENU
    WM_SYSKEYUP nVirtKey:VK_CONTROL
    WM_KEYUP nVirtKey:VK_MENU
    Why does the key generate 2 messages `VK_CONTROL` and `VK_MENU`? Why is the type of `VK_CONTROL` SYS (system) while `VK_MENU` non-system?

  2. #2
    2kaud's Avatar
    2kaud is offline Super Moderator Power Poster
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    Re: Alt key virtual codes

    WM_SYSKEYUP is sent when a system key is released (a system key is one when the ALT key is already pressed). WM_KEYUP is sent when a non-system key is released (ALT key is not also pressed). Similar for WM_SYSKEYDOWN and WM_KEYDOWN.

    VK_MENU is the ALT key. VK_CONTROL is the CTRL key. So you're pressed the CTRl key, then the ALT key (so WM_KEYDOWN rather than WM_SYSKEYDOWN as ALT is not already pressed), then released the CTRL key (WM_SYSKEYUP as ALT is pressed) then released the ALT key.

    See https://msdn.microsoft.com/en-us/lib...(v=vs.85).aspx
    All advice is offered in good faith only. All my code is tested (unless stated explicitly otherwise) with the latest version of Microsoft Visual Studio (using the supported features of the latest standard) and is offered as examples only - not as production quality. I cannot offer advice regarding any other c/c++ compiler/IDE or incompatibilities with VS. You are ultimately responsible for the effects of your programs and the integrity of the machines they run on. Anything I post, code snippets, advice, etc is licensed as Public Domain https://creativecommons.org/publicdomain/zero/1.0/ and can be used without reference or acknowledgement. Also note that I only provide advice and guidance via the forums - and not via private messages!

    C++17 Compiler: Microsoft VS2017 (15.8.0)

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