Hi, just need help related with below code. It gets the title of the web pages. It works fine for some of the web sites but do not work and froze my visual web devlp. for some of the web sites. I do not understand why?


strRegex =

"<title> *((\b.*\b)*|\b.*) *</title>"

Regex =

New System.Text.RegularExpressions.Regex(strRegex)

Dim matcha As Match = Regex.Match(resultslink, strRegex)

If matcha.Success Then

objCommand.Parameters(

"@productname").Value = matcha.Groups(1).Value()

End If

do not work for this webpage
http://www.teknosepet.com/?urun-detay_39070_Samsung_PL_50_10_2Mp_2_7_inc_LCD_Dijital_Fotograf_Makinesi_Turkce_Menu__45TL_Degerinde_2_GB_Hafiza_Karti___Tripod_Hediyeli_____Stoktan_Ayni_Gun_Kargo___Anadolu_Grup_Garantisinde__.html

resultslink is a string that contains the html of the above webpage.

Dim pattern As String = "<title>(?<Title>[^<]*)<\/title>"

Dim rx As New Regex(pattern, RegexOptions.IgnoreCase)
Dim m As Match = rx.Match(resultslink)
If (m.Success) Then
objCommand.Parameters.Add("@productname").Value = m.Groups("Title").Value
End If

---

John Grove - TFD Group, Senior Software Engineer, EI Division, http://www.tfdg.com

Erdem,
Your pattern "works" for some, but "freezes" for others because of "backtracking". Regular expressions making use of alternations (|) and the repetition symbols '*', and '+' can go exponential on some long strings that match or nearly match. Though technically not frozen, it might as well be frozen for very long strings. If you want to prove it to yourself, you can create several test Titles and try your pattern on them. Increase their length one character at a time until you start seeing the execution time increase. You can usually avoid the problem with a simpler pattern.

John's pattern should work for you unless you are trying to eliminate beginning and trailing spaces from your capture. In that case, use the Trim() method or function.

---

Les Potter, Xalnix Corporation, Yet Another C# Blog

Dim pattern As String = "<title>(?<Title>[^<]*)<\/title>"

Dim rx As New Regex(pattern, RegexOptions.IgnoreCase)
Dim m As Match = rx.Match(resultslink)
If (m.Success) Then
objCommand.Parameters.Add("@productname").Value = m.Groups("Title").Value
End If

---

John Grove - TFD Group, Senior Software Engineer, EI Division, http://www.tfdg.com

Erdem,
Your pattern "works" for some, but "freezes" for others because of "backtracking". Regular expressions making use of alternations (|) and the repetition symbols '*', and '+' can go exponential on some long strings that match or nearly match. Though technically not frozen, it might as well be frozen for very long strings. If you want to prove it to yourself, you can create several test Titles and try your pattern on them. Increase their length one character at a time until you start seeing the execution time increase. You can usually avoid the problem with a simpler pattern.

John's pattern should work for you unless you are trying to eliminate beginning and trailing spaces from your capture. In that case, use the Trim() method or function.

---

Les Potter, Xalnix Corporation, Yet Another C# Blog

thank you so much, your code works perfectly

thanks fordetailed information and clarification,

Good point Les:

Dim pattern As String = "<title>(?<Title>[^<]*)<\/title>"

Dim rx As New Regex(pattern, RegexOptions.IgnoreCase)
Dim m As Match = rx.Match(resultslink)
If (m.Success) Then
objCommand.Parameters.Add("@productname").Value = m.Groups("Title").Value.Trim()
End If

---

John Grove - TFD Group, Senior Software Engineer, EI Division, http://www.tfdg.com