Know Dot Net Article

Parsing with Regular Expressions - All-Alpha-Character String

by Les Smith and Brian Davis

Is there a function in .NET that will determine if all characters in a string are Alpha?  There is no intrinsic function in .NET or VB6 to do this, but the following functions show the VB6 and .NET methods of accomplishing this.  Moving from Clipper over 10 years ago, I wrote a VB3 function to replace the Clipper IsAllAlpha function.  The code for that method is shown below.

   Function IsALLAlpha(ByVal cS As String) As Boolean
      Dim i As Integer = 0
      Dim nc As String ' next character
      Dim AsciiVal As Integer

      If cS.Length = 0 Then Return False

      For i = 0 To cS.Length - 1
         nc = cS.Substring(i, 1)
         AsciiVal = Asc(nc)
         If Not ((AsciiVal > 64 And AsciiVal < 91) Or _
                (AsciiVal > 96 And AsciiVal < 123)) _<BR>                 Then
            Return False
         End If
      Next i
      Return True
   End Function

In .NET, the function shown above, can be replaced with the Regular Expression functionality shown below.  The code is not only much simpler, but faster.

   Public Function IsALLAlpha(ByVal Source As String) As Boolean
      'Returns True if the string contains only a-z and A-Z or string is empty
      'Returns False otherwise
      ' the expression says,
      ' beginning with the first char of the string (^),
      ' ensure that zero or more (*) chars are all alpha
      Return Regex.IsMatch(Source, "^[a-zA-Z]*$")
   End Function