The hexadecimal code is a base-16 number system used in various programming languages. It consists of 16 digits: 0-9 and A-F (A being equivalent to 10, B equivalent to 11, C equivalent to 12, D equivalent to 13, E equivalent to 14, and F equivalent to 15).
In the given context, &H1 is a hexadecimal representation of the decimal number 1. Similarly, &H8000 represents the decimal number 32768.
The "&H" prefix in Visual Basic (Classic) denotes that the following value is represented in hexadecimal format. When working with keyboard input functions like GetKeyState, it's essential to understand how these hexadecimal codes are used.
When checking for the status of a virtual key using GetKeyState, you can use bitwise AND operations to determine if the key is pressed or not. The high-order bit (the leftmost bit) in the return value indicates whether the key is down (1) or up (0). If the low-order bit is 1, it means the key is toggled.
For example, when checking for the ALT key, you would use &H12 and assign it the value of &H8000. This ensures that only the high-order bit is considered, effectively ignoring any other bits.
Practical Example: Checking for ALT Key Press
To illustrate this concept further, consider a function that copies text from an input box to the clipboard when the user selects ALT and X. Here's a sample code snippet:
```vb
Public Const VK_ALT = &H12
Public Type KBDLLHOOKSTRUCT
vkCode As Long ' virtual keycode
scanCode As Long ' hardware scancode
flags As Long
time As Long
dwExtraInfo As Long
End Type
Dim IsALT As Boolean
IsALT = (GetKeyState(VK_ALT) And &H8000) 'Ctrl Key
tempVKCodeHolder = correctedInputValues(CInt(Trim(HookStruct.vkCode))) 'Takes the interpreted keyboard input value and translates it to its proper ascii value.
If ((IsAlt = True) And (tempVKCodeHolder = 88)) Then
' If ALT and "X" are pressed at the same time,
' the user's data Copied to the Clipboard.
Clipboard.Clear
Clipboard.SetText(strUserInput)
Exit Function
End If
```
In this code, we first define the VK_ALT constant with a hexadecimal value of &H12. We then use GetKeyState to check if the ALT key is pressed. The bitwise AND operation (&H8000) ensures that only the high-order bit is considered, effectively ignoring any other bits.
By understanding how hexadecimal codes are used in Visual Basic (Classic), developers can create more accurate and efficient keyboard input handling functions.
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