How do I parse HTML using regular expressions in C#?

Question

For example, given HTML code

<s2> t1 </s2>  <img src='1.gif' />  <span> span1 <span/>

I am trying to obtain

1.  <s2>
2.  t1
3. </s2>
4. <img src='1.gif' />
5. <span>
6. span1
7. <span/>

How do I do this using regular expressions in C#?

In my case, the HTML input is not well-formed XML like XHTML. Therefore I can not use XML parsers to do this.

How to rewrite **what** regular expression? Please rephrase your question. Your samples are unreadable. — Michael Petrotta, Oct 15 '09 at 01:54
Your question doesn't make sense. You say you want to parse HTML, but the example code you posted isn't HTML. — Jörg W Mittag, Oct 15 '09 at 02:41
Canonical question: *[RegEx match open tags except XHTML self-contained tags](http://stackoverflow.com/questions/1732348/)* — Peter Mortensen, Nov 11 '14 at 00:03

score 6 · Answer 1 · answered Oct 15 '09 at 01:57

6

Regular expressions are a very poor way to parse HTML. If you can guarantee that your input will be well-formed XML (i.e. XHTML), you can use XmlReader to read the elements and then print them out however you like.

answered Oct 15 '09 at 01:57

bobbymcr

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In my case, the input is NOT well-formed xml. – Mike108 Oct 15 '09 at 02:07
3

Then you're in for a very complex problem, in general... HTML parsing with all of its implied elements, optional end tags, etc. is no fun. However, you might be able to leverage an existing library, such as... http://www.codeplex.com/htmlagilitypack – bobbymcr Oct 15 '09 at 02:10
2

No, regular expressions are *not* "a poor way to parse HTML", because that would imply that regular expressions can parse HTML *at all*, which is not the case. It is mathematically proven that regular expressions *cannot* parse HTML. In fact, pretty much every college student has to prove this at some point during a homework assignment or exam or something. – Jörg W Mittag Oct 15 '09 at 02:39

score 4 · Answer 2 · answered Oct 15 '09 at 02:36

This has already been answered literally dozens of times, but it bears repeating: regular expressions can only parse regular languages, that's why they are called regular expressions. HTML is not a regular language (as probably every college student in the last decade has proved at least once), and therefore cannot be parsed by regular expressions.

score 3 · Answer 3 · answered Oct 15 '09 at 02:12

3

You might want to try the Html Agility Pack, http://www.codeplex.com/htmlagilitypack. It even handles malformed HTML.

answered Oct 15 '09 at 02:12

nickytonline

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score 0 · Accepted Answer · answered Oct 15 '09 at 03:05

0

I used this regx in C#, and it works. Thanks for all your answers.

<([^<]*)>|([^<]*)

answered Oct 15 '09 at 03:05

Mike108

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It works with the data you've tested it with. If that's all the data you ever need to process with it, then fine. – Robert Rossney Oct 15 '09 at 06:38
If not: now you've got two problems. – Peter Hoffmann Oct 15 '09 at 23:44

score -3 · Answer 5 · answered Oct 15 '09 at 02:33

-3

you might want to simply use string functions. make < and > as your indicator for parsing.

answered Oct 15 '09 at 02:33

junmats

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How do I parse HTML using regular expressions in C#?

5 Answers5

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