How to extract values ​​of characters used with Shift key using MapVirtualKeyEx API?

Question

I use the MapVirtualKeyEx api to extract characters from the virtual keys on the keyboard.

Here is the code in VB.

Const MAPVK_VK_TO_CHAR = 2

Dim keyblayoutID As Integer = GetKeyboardLayout(0)

For nb As Integer = 0 To 255
    Dim ScanCode As UInteger = MapVirtualKeyEx(nb, MAPVK_VK_TO_CHAR, keyblayoutID)
    If ScanCode <> 0 Then
        ScanCode = ScanCode And &HFF
        Debug.Print(ChrW(ScanCode) & " - " & Hex(nb))
    End If
Next

Here is a part of the result display

The result displayed is correct.

For OEM virtual keys, I would like to retrieve the character when the shift key is pressed.

Example: Virtual key: 0xBB, currently gives me the character '=', I would like to retrieve the character '+' when the shift key is pressed.

Is it possible to use the API with the value of the virtual code and the meaning of the shift key pressed?

Answer 1

You can use ToUnicodeEx

A test in a Button click :

Imports System.Runtime.InteropServices
Imports System.Text

Public Class Form1

    <DllImport("User32.dll", SetLastError:=True, CharSet:=CharSet.Unicode)>
    Public Shared Function ToUnicodeEx(wVirtKey As UInteger, wScanCode As UInteger, lpKeyState As Byte(),
                                 <Out, MarshalAs(UnmanagedType.LPWStr)> pwszBuff As StringBuilder,
                                 cchBuff As Integer, wFlags As UInteger, dwhkl As IntPtr) As Integer
    End Function

    <DllImport("User32.dll", SetLastError:=True, CharSet:=CharSet.Unicode)>
    Public Shared Function GetKeyboardState(lpKeyState As Byte()) As Boolean
    End Function

    <DllImport("User32.dll", SetLastError:=True, CharSet:=CharSet.Unicode)>
    Public Shared Function GetKeyboardLayout(idThread As UInteger) As IntPtr
    End Function

    <DllImport("User32.dll", SetLastError:=True, CharSet:=CharSet.Unicode)>
    Public Shared Function MapVirtualKeyEx(uCode As UInteger, uMapType As UInteger, dwhkl As IntPtr) As UInteger
    End Function

    Private Function GetCharFromVirtualKey(virtualKey As UInteger, shiftPressed As Boolean) As Char
        Dim keyState(255) As Byte
        GetKeyboardState(keyState)

        If shiftPressed Then
            keyState(&H10) += &H80 ' Simulate Shift key press
        End If

        Dim nScanCode As UInteger = MapVirtualKeyEx(virtualKey, 0, GetKeyboardLayout(0))
        If (nScanCode <> 0) Then
            Dim sb As New StringBuilder(2)
            Dim nResult As Integer = ToUnicodeEx(virtualKey, nScanCode, keyState, sb, sb.Capacity, 0, GetKeyboardLayout(0))
            If nResult > 0 Then
                Return If(String.IsNullOrEmpty(sb(0)), " ", sb(0))
            Else
                Return ChrW(0)
            End If
        End If
        Return ChrW(0)
    End Function

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        For nVK As Integer = 0 To 255
            Dim sUnshifted As Char = GetCharFromVirtualKey(CUInt(nVK), False)
            Dim sShifted As Char = GetCharFromVirtualKey(CUInt(nVK), True)
            If sUnshifted <> ChrW(0) And sShifted <> ChrW(0) Then
                Debug.WriteLine($"VK: {nVK:X2} - Unshifted: '{sUnshifted}' Shifted: '{sShifted}'")
            End If
        Next
    End Sub
End Class