Detect or Get Keypress

[raleep]

I apologise for not doing more research on my own.  I have searched MSDN, but the simple (I think) information I want seems to be buried in masses of what is not immediately useful to me.

I think GetAsyncKeyState would do it if invoked once for each key (as well as once at the start of the routine I want to pause).

I am looking for a function that when called will return when and only when (although a forced return would also be nice) a key is pressed - any key.

Can anyone suggest an answer or a direction for further research?

Thank you - Robert Leeper

[raleep]

I am looking for a function that when called will return when and only when (although a forced return would also be nice) a key is pressed - any key.

Never mind about the forced return - I see how to do [something like] that.

[dedndave]

if you're talking about console-mode programs, i suggest crt__getch
it's part of the msvcrt library
but, the console is buggish, and the library often yields best results

for GUI-mode programs, you write a handler in WndProc
it activates when a key is pressed, but allows other processing when no key is in the buffer

[rrr314159]

Hello raleep,

Don't really think this is what you want but at least it's a starting point

Code Select Expand

include \masm32\include\masm32rt.inc

.data
    thechar db 0, 0
    format db 'You pressed %s',10,0
.code

start:
    print "Press any key, ctrl-C to exit", 10, 0
    @@:
        call wait_key
        mov thechar, al
        invoke crt_printf, ADDR format, ADDR thechar
    jmp @B
    ret

end start

Assume you know how to run this with masm32

wait_key is using the function dedndave mentioned, crt__getch, and can be found in \masm32\m32lib\wait_key.asm

[MichaelW]

Assuming that your goal here is to detect key presses in your app, and not in other apps, crt__getch is easy, and while it cannot detect "any" key it can detect all but the shift and toggle keys.

Edit: modified code to display the return value as a number and a character.

Code Select Expand


;===============================================================================
include \masm32\include\masm32rt.inc
;===============================================================================
.data
.code
;=============================================================================== 
start: 
;===============================================================================     
  @@:
    invoke crt__getch
    cmp   eax, "X"
    je    @F
    cmp   eax, "x"
    je    @F
    printf("%d\t%c\n",eax,eax)
    jmp   @B
  @@: 
    inkey
    exit
end start
;===============================================================================



[dedndave]

hi Michael,

as i recall, _getch IS capable of detecting all keys except system keys (ALT-?) and CTRL-C (CTRL-Break)
if you want to detect CTRL-Break, install a handler for it

if it returns 0 or 0E0h on the first call, it must be called again (arrow keys, function keys, etc)
very similar to how the old 16-bit INT 16h worked

here is a function that returns immediately if no key has been pressed (non-blocking)
it's one i have used often
give me a few minutes, and i can adapt it to a blocking function

Code Select Expand

;*************************************************************************

InKyb   PROC

;Polled Keyboard Input - DednDave 8, 2010
;
;This function returns a keystroke in EAX if there is one in the buffer.
;If the buffer is empty, the function returns immediately.
;
;If the keyboard buffer is empty, AH = 0, AL = 0, ZF = 1.
;If the stroke is a regular key, AH = 0, AL = key char, ZF = 0.
;If the stroke is an extended key, AH = extended key, AL = E0h, ZF = 0.
;If the stroke is a function key, AH = function key, AL = 0, ZF = 0.
;
;ECX, EDX are not preserved.

        call    crt__kbhit
        or      eax,eax
        jz      InKyb1

        call    crt__getch
        and     eax,0FFh
        jz      InKyb0

        cmp     al,0E0h
        jnz     InKyb1

InKyb0: push    eax
        call    crt__getch
        pop     edx
        shl     eax,8
        or      eax,edx

InKyb1: retn

InKyb   ENDP

;*************************************************************************

[dedndave]

here - give this a try....

[MichaelW]

Dave, from a 32-bit app running under Windows 7-64 the _getch function does not return until you press a non-toggle or non-shift key. And, one that I forgot to test, it does not return when you press the Pause/Break key. The arrow and function keys work as you describe, returning 0E0h ahead of the arrow keys and 0 ahead of the function keys.

MSDN _getch _getwch

And your app behaves the same way, not responding to the shift, toggle, or Pause/Break keys.

[dedndave]

that's strange
under XP (32-bit), shift , caps lock, and num lock work as expected
even many of the CTRL keys work

ALT keys are system keys, which msvcrt authors chose not to override - understandably

[MichaelW]

The key combinations involving the shift and toggle keys, or at least the ones that I tested, work as expected. _getch, like most or all high-level input functions, does not meet the "any key" requirement because it does not detect the shift or toggle keys when they are pressed as single keys. Perhaps I should have interpreted "any key" as "any normal key".

[dedndave]

you can use one of the console API functions to "get any key"
really, i try not to spend too much time on it, because the console is buggish
no matter what you do, you get buggish behavior   :P

to me, it works fine for simple test programs or tools in "teletype" fashion
i.e., print a line, get a line - no fancy cursor movement stuff

[dedndave]

here's one that uses ReadConsoleInput...

Code Select Expand

;***********************************************************************************************

AnyKey  PROC

;Wait for Any Console Key Press - DednDave
;version 1, 12-2011
;version 2, 2-2013
;
;  This function returns when any console key is pressed (bKeyDown = 1).
;A possible drawback is that all input event records are removed from
;the console input queue until a key is pressed. In many cases, this is
;not an issue. The virtual key code, virtual scan code, TCHAR character,
;and control key state values are returned in registers.

;Call With: Nothing
;
;  Returns: EAX = TCHAR character (high word of EAX = 0)
;           ECX = control key state flags
;               Bit   Name                Meaning
;                0    RIGHT_ALT_PRESSED   Right ALT key is pressed
;                1    LEFT_ALT_PRESSED    Left ALT key is pressed
;                2    RIGHT_CTRL_PRESSED  Right CTRL key is pressed
;                3    LEFT_CTRL_PRESSED   Left CTRL key is pressed
;                4    SHIFT_PRESSED       SHIFT key is pressed
;                5    NUMLOCK_ON          NUM LOCK light is on
;                6    SCROLLLOCK_ON       SCROLL LOCK light is on
;                7    CAPSLOCK_ON         CAPS LOCK light is on
;                8    ENHANCED_KEY        Key is enhanced
;           EDX:
;           low word (DX) = virtual key code
;               high word = virtual scan code
;
;           all other registers are preserved

;-------------------------------------------------

    LOCAL   ir          :INPUT_RECORD
    LOCAL   uRecCnt     :UINT
    LOCAL   hStdInp     :HANDLE

;-------------------------------------------------

    INVOKE  GetStdHandle,STD_INPUT_HANDLE
    mov     hStdInp,eax
    .repeat
        INVOKE  ReadConsoleInput,hStdInp,addr ir,1,addr uRecCnt
        movzx   ecx,word ptr ir.EventType
        mov     edx,dword ptr ir.KeyEvent.wVirtualKeyCode
    .until (ecx==KEY_EVENT) && (ecx==ir.KeyEvent.bKeyDown) && (dx!=VK_SHIFT) && (dx!=VK_CONTROL) && (dx!=VK_MENU)
    movzx   eax,word ptr ir.KeyEvent.UnicodeChar
    mov     ecx,ir.KeyEvent.dwControlKeyState
    ret

AnyKey  ENDP

;***********************************************************************************************

it doesn't mention it, but that one is UNICODE aware, i think

notice that you can modify this line to customize behaviour for different key sets

Code Select Expand

    .until (ecx==KEY_EVENT) && (ecx==ir.KeyEvent.bKeyDown) && (dx!=VK_SHIFT) && (dx!=VK_CONTROL) && (dx!=VK_MENU)

[raleep]

if you're talking about console-mode programs, i suggest crt__getch
it's part of the msvcrt library
but, the console is buggish, and the library often yields best results

for GUI-mode programs, you write a handler in WndProc
it activates when a key is pressed, but allows other processing when no key is in the buffer

Code Select Expand


sbrtst_test:
call beep0
pushad
call wosw
invoke crt__getch
popad
   jmp sbrtst_test

This doesn't work for me; it just goes on beeping until stopped.

[jj2007]

Old-fashioned but seems to work:

Code Select Expand

include \masm32\include\masm32rt.inc

.data?
kb1 db 256 dup(?)
kb2 db 256 dup(?)

.code
start:
  mov esi, offset kb1
  mov edi, offset kb2
  .Repeat
invoke GetKeyboardState, esi
.Repeat
invoke Sleep, 1
invoke GetKeyState, VK_SHIFT
invoke GetKeyboardState, edi
mov ecx, 255
push esi
push edi
repe cmpsb
pop edi
pop esi
.Until sdword ptr ecx>0
neg cl
sub cl, 2
.Break .if ecx==VK_ESCAPE
print str$(ecx), " was pressed", 13, 10
  .Until 0
  print "bye"
  exit
end start

[dedndave]

Code Select Expand

sbrtst_test:
call beep0
pushad
call wosw
invoke crt__getch
popad
   jmp sbrtst_test

that code will continually loop and beep whenever a key is pressed

first of all, the PUSHAD/POPAD preserves and restores all the registers, including EAX
crt__getch returns a value in EAX that should be tested for key-presses (destroyed by POPAD)
and - you don't display that value

also, the loop ends with an unconditional branch back to the top
you may way to use a conditional branch, instead