Question

This is a piece of Visual Basic code which gives an exception, FormatException.

Suppose my hex value, variable hexValue, is 424E0A78. The code works properly. The moment hexValue gets a value (say) 424EA78, this exception occurs:

The supplied hex value is either empty or in an incorrect format. Use the following format: 00000000

Is there a solution?

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Try
        Dim hexValue As String = "424E0A78"

        Dim iInputIndex As Integer = 0
        Dim iOutputIndex As Integer = 0
        Dim bArray(3) As Byte 'creating an array
        Dim rnum As Integer
        Dim rArray(3) As Byte
        Dim rSingle As Single
        Dim rSingle1 As Single
        Dim rSingle2 As Single
        Dim rStr As Integer
        Dim rnewArray(3) As Byte ' variables
        Dim rnum2, rnum3 As Integer 'variables
        Dim rstr2, rstr3 As String

        'For iInputIndex = 0 To hexValue.Length - 1 Step 2
        For iInputIndex = 0 To hexValue.Length - 1 Step 2

            'rnum3 = hexValue.Chars(iInputIndex) * 16

            'REjina code starts
            rStr = 0
            rstr2 = hexValue.Chars(iInputIndex)
            If (rstr2 = "A") Then
                rstr2 = 10
            ElseIf (rstr2 = "B") Then
                rstr2 = 11
            ElseIf (rstr2 = "C") Then
                rstr2 = 12
            ElseIf (rstr2 = "D") Then
                rstr2 = 13
            ElseIf (rstr2 = "E") Then
                rstr2 = 14
            ElseIf (rstr2 = "F") Then
                rstr2 = 15
            End If

            rStr = Val(rstr2) * 16

            'Second rejina conversion
            rstr2 = hexValue.Chars(iInputIndex + 1)
            If (rstr2 = "A") Then
                rstr2 = 10
            ElseIf (rstr2 = "B") Then
                rstr2 = 11
            ElseIf (rstr2 = "C") Then
                rstr2 = 12
            ElseIf (rstr2 = "D") Then
                rstr2 = 13
            ElseIf (rstr2 = "E") Then
                rstr2 = 14
            ElseIf (rstr2 = "F") Then
                rstr2 = 15
            End If

            rStr = rStr + Val(rstr2)

            'rstr2 = hexValue.Chars(iInputIndex + 1)
            rnewArray(iOutputIndex) = rStr
            'rejina code ends

            'rArray(iOutputIndex) = Byte.Parse(hexValue.Chars(iInputIndex) & hexValue.Chars(iInputIndex + 1), Globalization.NumberStyles.HexNumber)

            'bArray(iOutputIndex) = Convert.ToByte(hexValue.Chars(iInputIndex))

            iOutputIndex += 1
        Next

        'Array.Reverse(rArray)

        'rejina code starts
        Array.Reverse(rnewArray)
        'rejina code ends

        'Array.Reverse(bArray)


        'rSingle = BitConverter.ToSingle(rArray, 0)
        'rejina code starts
        rSingle1 = BitConverter.ToSingle(rnewArray, 0)
        'rejina code ends
        'rSingle2 = BitConverter.ToSingle(bArray, 0)

        MessageBox.Show(rSingle1)

        'Return BitConverter.ToSingle(rnewArray, 0)
    Catch ex As Exception
        Throw New FormatException("The supplied hex value is either empty or in an incorrect format. Use the following format: 00000000", ex)
    End Try
End Sub

Answer 1

If the input string had an odd (i.e. not even) length then you’ll get an array index out of bounds exception on the line:

hexValue.Chars(iInputIndex + 1)

…which is most likely what you’re experiencing here.