Compiling Regular Expressions

Using A Compiled RegEx

Using the compiled RegEx is just like using any other object. Add a reference to it using the Project Properties dialog:

1. Right-click the project and select Add Reference...
2. Browse to the location of the assembly and select it.

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Using a compiled RegEx is the same as any other object.

Dim myCompiledRegex As New myRegExNS.myRegExType
Dim RegExResult As Boolean
RegExResult = myCompiledRegex.IsMatch("String to Match")

But just how much will this speed up your application? Let's find out.

I borrowed the timing code from my StringBuilder article and simply changed the variables a bit and had this running in a few minutes ...

Imports System.Diagnostics
Imports System.Text.RegularExpressions

Public Class CompiledRegEx
   Dim InlineTimeSpan As Integer
   Dim CompiledTimeSpan As Integer
   Dim LoopLimit As Integer
   Dim PhoneNum(9999) As String
   Dim I As Integer

   Private Sub TimeEm_Click( ...
      If UseInline.Checked Then UseInlineTest()
      If UseCompiled.Checked Then UseCompiledTest()
      CalcImprovement()
   End Sub

   Private Sub UseInlineTest()
      Dim myRegexString As New Regex( _
         "^1?\s*-?\s*(\d{3}|\(\s*\d{3}\s*\))" & _
         "\s*-?\s*\d{3}\s*-?\s*\d{4}$")
      Dim RegExResult As Boolean
      Dim myStopwatch As Stopwatch = New Stopwatch
      Dim myTimeSpan As New TimeSpan
      myStopwatch.Reset()
      myStopwatch.Start()
      For I = 0 To LoopLimit
         RegExResult = _
            myRegexString.IsMatch(PhoneNum(I).ToString)
      Next
      myStopwatch.Stop()
      myTimeSpan = myStopwatch.Elapsed
      InlineTimeSpan = myTimeSpan.Milliseconds
      UsingInline.Text = myTimeSpan.ToString
   End Sub

   Private Sub UseCompiledTest()
      Dim myStopwatch As Stopwatch = New Stopwatch
      Dim myCompiledRegex As New myRegExNS.myRegExType
      Dim RegExResult As Boolean
      Dim myTimeSpan As New TimeSpan
      myStopwatch.Reset()
      myStopwatch.Start()
      For I = 0 To LoopLimit
         RegExResult = _
            myCompiledRegex.IsMatch(PhoneNum(I).ToString)
      Next
      myStopwatch.Stop()
      myTimeSpan = myStopwatch.Elapsed
      CompiledTimeSpan = myTimeSpan.Milliseconds
      UsingCompiled.Text = myTimeSpan.ToString
   End Sub

   Private Sub CalcImprovement()
      Try
         Improvement.Text = _
            CStr((InlineTimeSpan / CompiledTimeSpan))
      Catch ex As Exception
         Improvement.Text = ""
      End Try
   End Sub

   Private Sub CompiledRegEx_Load( ...
      Dim PhoneNumSuf As Integer = 0
      Dim PhoneNumPre As String = "123-555-"
      LoopLimit = CInt(NumberOfIterations.Text) - 1
      For I = 0 To LoopLimit
         PhoneNum(I) = _
            PhoneNumPre & I.ToString.PadLeft(4, "0"c)
      Next
   End Sub
End Class

The result showed a very significant improvement of about 30 to 50 percent, but frankly, I expected more. On the next page, we get more.

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