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How to use ToAscii properly

Posted on 2004-08-27
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Last Modified: 2008-01-09
I'm trying to use the ToAscii function. I keep trying to follow examples I found on the net but whenever I try them, I always get an overflow error.
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Question by:psybustermk3
10 Comments
 
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Expert Comment

by:Jenn3
Comment Utility
Maybe you could showing the example...
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Author Comment

by:psybustermk3
Comment Utility
Ok. Sorry about that.

Private Type KeyboardBytes
     kbByte(0 To 255) As Byte
End Type

Private Type KeyCaptured
    kchByte(0 To 1) As Byte
End Type

Dim Hookstruct As KBDLLHOOKSTRUCT
Dim keybstate As KeyboardBytes
Dim keychar As KeyCaptured

released = ToAscii(Hookstruct.vkCode, MapVirtualKey(Hookstruct.vkCode, 0), VarPtr(keybstate), VarPtr(keychar), 0)

I think I'm doing something wrong with the pointers but I can't figure out what.
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Author Comment

by:psybustermk3
Comment Utility
Increasing point.
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LVL 3

Expert Comment

by:nichia
Comment Utility
It's always a good idea to first assign local variables with the values before passing them to functions.  It makes for easier debugging and error handling.

The third parameter in ToAscii() wants to see a byte value (lpbKeyState As Byte).  You are assigning it the return value of VarPtr() which is a long.  This is the source of the error.

This is easier to read, but it still contains the error:

    On Error GoTo errhandler
    Dim Released As Long
    Dim lVirtKey As Long, lScanCode As Long, lpbKeyState As Byte, lpwTransKey As Long
    lVirtKey = Hookstruct.vkCode
    lScanCode = MapVirtualKey(Hookstruct.vkCode, 0)
    lpbKeyState = VarPtr(keybstate)
    lpwTransKey = VarPtr(keychar)
   
    Released = ToAscii(lVirtKey, lScanCode, lpbKeyState, lpwTransKey, 0)
    Exit Sub
errhandler:
    Call MsgBox("Error: " & Err.Number & " : " & Err.Description, vbCritical, "Error Message")
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Expert Comment

by:GrahamSkan
Comment Utility
It might help to show the ToAscii declaration (which I have found using the API viewer) and the KBDLLHOOKSTRUCT definition, which I can't.
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LVL 3

Expert Comment

by:nichia
Comment Utility
OK.  The declare for ToAscii in the API viewer must be incorrect.  A pointer to a byte array cannot be a byte!

I searched for alternative delcares and I found:

Declare Function ToAscii Lib "Keyboard" (ByVal wVirtKey As Integer, ByVal wScanCode As Integer, lpKeyState As Any, lpChar As Any, Byval wFlags As Integer) As Integer

Here, the pointers are declared as Any, meaning they will accept the pointer from VarPtr.  See if this works for you.

Be sure to declare lpbKeyState As Long, not Byte if you use my sample code above.

Good Luck!
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Accepted Solution

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nichia earned 130 total points
Comment Utility
Oops!  That declare is for 16 bit windows.  Try using this declare:

Declare Function ToAscii Lib "user32" (ByVal wVirtKey As Long, ByVal wScanCode As Long, lpKeyState As Any, lpChar As Any, Byval wFlags As Long) As Long
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Author Comment

by:psybustermk3
Comment Utility
I tried nichia idea and the errors were gone. But I can't find the output ASCII character which is suppose to be in keychar.
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Author Comment

by:psybustermk3
Comment Utility
Ok. I made it work by using a long type variable without using varptr.

Private Type KeyboardBytes
     kbByte(0 To 255) As Byte
End Type

Private Declare Function ToAscii Lib "user32" (ByVal wVirtKey As Long, ByVal wScanCode As Long, lpKeyState As KeyboardBytes, lpChar As Any, ByVal wFlags As Long) As Long

Dim Hookstruct As KBDLLHOOKSTRUCT
Dim keybstate As KeyboardBytes
Dim keychar As Long
Dim released as Integer

released = ToAscii(Hookstruct.vkCode, MapVirtualKey(Hookstruct.vkCode, 0), VarPtr(keybstate), VarPtr(keychar), 0)

I accept nichia's answer since even if it's not exactly the answer, it's the closest one.

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Author Comment

by:psybustermk3
Comment Utility
I forgot to change the code. My mistake.

released = ToAscii(Hookstruct.vkCode, MapVirtualKey(Hookstruct.vkCode, 0), VarPtr(keybstate), keychar, 0)
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