Unable to convert php regex to C# regex

Question

I want to count links which are having special symbol (underscore) . I have written regex its working fine in an online editor/php editor, but not working in C# code:

<
  (?<Tag_Name>(a)|img)\b
  [^>]*?
  \b(?<URL_Type>(?(2)href|src))
  \s*=\s*
  (?:"(?<URL>(?:\\.|[^\\"_#?&]++)*(?:_|(?<Query>[#?&]))(?:\\.|[^"\\]++)*)"
  |  '(?<URL>(?:\\.|[^\\'_#?&]++)*(?:_|(?<Query>[#?&]))(?:\\.|[^'\\]++)*)')

but in C# code its giving compilation error

MatchCollection underscoreLinks = Regex.Matches(strIn, "<(?<Tag_Name>(a)|img)\b[^>]*?\b(?<URL_Type>(?(2)href|src)) \s*=\s*(?:"(?<URL>(?:\\.|[^\\"_#?&]++)*(?:_|(?<Query>[#?&]))(?:\\.|[^"\\]++)*)"|  '(?<URL>(?:\\.|[^\\'_#?&]++)*(?:_|(?<Query>[#?&]))(?:\\.|[^'\\]++)*)')", RegexOptions.IgnoreCase | RegexOptions.Multiline);

can u check it this < (?(a)|img)\b [^>]*? \b(?(?(2)href|src)) \s*=\s* (?:"(?(?:\\.|[^\\"_]++)*_(?:\\.|[^"\\]++)*)" | '(?(?:\\.|[^\\'_]++)*_(?:\\.|[^'\\]++)*)') its not working same issue — krishna mohan, Nov 14 '15 at 12:06
It's exactly the same issue, so the same answer applies. I believe if you understand the answer I wrote you'd be able to correct this on your own. — Mariano, Nov 14 '15 at 12:24
but unable to do this ...please help ]*\balt\s*=\s*"[^"]+")[^>]+> — krishna mohan, Nov 14 '15 at 12:26
hai this is giving compilation error , can u convert to c# plz ]*\balt\s*=\s*"[^"]+")[^>]+> — krishna mohan, Nov 14 '15 at 12:40
I'm sorry, but I believe that is already covered in the answer. I'd recommend reading this post: [Can I escape a double quote in a verbatim string literal?](http://stackoverflow.com/a/1928943/5290909) — Mariano, Nov 14 '15 at 12:47
should i add one more double quote at the place of double quote? — krishna mohan, Nov 14 '15 at 12:55
To test a .Net RegEx you can try http://regexhero.net/tester/ — Oliver, Nov 17 '15 at 11:27
@Oliver The syntax to escape a quote is not related to regex — Mariano, Nov 18 '15 at 14:59

score 3 · Answer 1 · edited May 23 '17 at 12:15

There are some things you need to correct:

You're using single backslashes, which are parsed by the .net interpreter before they're passed to regex. Use a verbatim string instead, ie: @"pattern"
You have unescaped quotes in your string. To escape them in a verbatim string, use 2 double quotes: @"the ""pattern"" with quotes".
.net does not support possessive quantifiers. Use an atomic group instead. i.e: change [^\\"_#?&]++ to (?>[^\\"_#?&]+).
You can use the same multiline syntax, ignoring whitespace, using RegexOptions.IgnorePatternWhitespace.

string pattern = @"
    <
      (?<Tag_Name>(a)|img)\b
      [^>]*?
      \b(?<URL_Type>(?(2)href|src))
      \s*=\s*
      (?:""(?<URL>(?>\\.|[^\\""_#?&]+)*(?:_|(?<Query>[#?&]))(?>\\.|[^""\\]+)*)""
      |  '(?<URL>(?>\\.|[^\\'_#?&]+)*(?:_|(?<Query>[#?&]))(?>\\.|[^'\\]+)*)')
    ";

Regex re = new Regex( pattern, 
                      RegexOptions.IgnoreCase | RegexOptions.Multiline
                      | RegexOptions.IgnorePatternWhitespace);

MatchCollection underscoreLinks = re.Matches(text);

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Unable to convert php regex to C# regex

1 Answers1