Question

I am working with ASP.NET and need to manage with a string typed by the user in order to extract some information. The user enters a normal text, words and numbers, but sometimes he may type a mathematical expression in MATHML, these expressions are always an xml string enclosed by the tag.
I want to extract from the typed text every math segment.
For example, let’s consider the user typed this text:

string input = "My name is Dorry and here is a math expression: <math>---some math1---</math> ah, there is another expression: <math>---some math2---</math> and do not forget this too <math>---some math3---</math>.".

Well, The first regex solution I came up with is this:

string pattern1 = @"\<math(.+)\<\/math\>";

To get matches I obviousely use:

Regex r = new Regex(pattern1, RegexOptions.IgnoreCase);
string[] res = r.Matches(input);

And it seemd working, too bad, it does not because this expression, instead of getting me an array (using Reges.Matches) filled with three strings (“—some math1—“, “—some math2—“, “—some math3—“); it gets me an array with one element only: “—some math1— ah, there is another expression: —some math2— and do not forget this too —some math3—“. Can you see? it takes the first and the last and merges everything in the middle WITHOUT CARING of some other or elements in the way!

Well, I suppose this is a well known issue about regular expressions; is there a solution? how to tell the regex engine to be a little more… aware?

Thank you very much in advance.

Answer 1

Give this a go..

string pattern1 = @"\<math[\s\S]*?<\/math\>";
Regex r = new Regex(pattern1, RegexOptions.IgnoreCase);
MatchCollection res = r.Matches(input);

Nick