C# Regex Can't Match Anything (Probably because can't escape characters properly)

Question

I make a regex pattern and tested in this site : http://rubular.com/

I'm writing this pattern exactly like this to the first box in that site.

<div class="product clearfix">\n+<div class="img">\n+<a href="(.*?)">\n+<img class="lazyload" id='.*' data-original="(.*?)" alt=".*" title="(.*?)" \/>

I left the second box empty.

My regex pattern working perfectly fine respect to this site.

But i can't get it working in C#

I'm trying this:

WebClient client = new WebClient();

string MainPage = client.DownloadString("http://www.vatanbilgisayar.com/cep-telefonu-modelleri/");

string ItemPattern = "<div class=\"product clearfix\">\\n+" +   //  <div class="product clearfix">\n
                "<div class=\"img\">\\n" +                  //  <div class="img">\n
                "+<a href=\"(.*?)\">\\n" +                  //  +<a href="(.*?)">\n
                "+<img class=\"lazyload\"" +                //  +<img class="lazyload"
                "id='.*' data-original=\"(.*?)\"" +         //  id='.*' data-original="(.*?)"
                "alt=\".*\" title=\"(.*?)\"\\/>";           //  alt=".*" title="(.*?)" \/>

MatchCollection matches = Regex.Matches(MainPage, ItemPattern);

foreach (Match match in matches)
{
    Console.WriteLine("Area Code:        {0}", match.Groups[1].Value);
    Console.WriteLine("Telephone number: {0}", match.Groups[2].Value);
    Console.WriteLine();
}

I simply escaped every " with \ . I really don't understand why it's not working and this starting to drive me crazy..

You escaped the quotes, but not the backslashes. Just use raw string literals (`@""`) instead. — Cameron, Dec 15 '14 at 22:45
Can you please write the final pattern which i should use? It will be easier to understand for me. — Trax, Dec 15 '14 at 22:48
First off, there is no way Jon's hat fits so well! Oh, and here is an SO question you might find relevant http://stackoverflow.com/questions/1732348/regex-match-open-tags-except-xhtml-self-contained-tags — supertopi, Dec 15 '14 at 22:52

score 4 · Accepted Answer · answered Dec 15 '14 at 22:48

4

You need 2 layers of escape sequences. You need to escape once for c# and once more for the regex syntax.

If you want to escape characters for regex have to escape \ too, so you should change your \ to \\ for escape sequences at the regex level

answered Dec 15 '14 at 22:48

Sam I am says Reinstate Monica

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Can you please write the final pattern which i should use? Because i tried as you say but it's not worked. – Trax Dec 15 '14 at 22:55
@user2617750 That would be a lot easier for me to do if you included the text that you're trying to get matches from – Sam I am says Reinstate Monica Dec 15 '14 at 23:43
Or use C#'s verbatim strings: `@""` – knittl Dec 15 '14 at 23:45

peege · Answer 2 · 2014-12-16T00:51:42.293

2

use TWO \'s for every single \ in your string. Not counting the escaping you already did for the quotes. Since \ is an escape character. It looks like mainly with "\n" occurring 3 times.

Original String:

"product clearfix">\n+<div class="img">\n+<a href="(.*?)">\n+<img class="lazyload" id='.*' data-original="(.*?)" alt=".*" title="(.*?)" \/

Also, you can break that up into more than one line. c# ignores spaces, so just close the quote and add a "+" to the end of the line, continue by starting with another quote.

C# String:

string ItemPattern = "<div class=\"product clearfix\">\\n" +   //  <div class="product clearfix">\n
                    "+<div class=\"img\">\\n" +                 //  +<div class="img">\n
                    "+<a href=\"(.*?)\">\\n" +                  //  +<a href="(.*?)">\n
                    "+<img class=\"lazyload\"" +                //  +<img class="lazyload"
                    "id='.*' data-original=\"(.*?)\"" +         //  id='.*' data-original="(.*?)"
                    "alt=\".*\" title=\"(.*?)\"\\/>";           //  alt=".*" title="(.*?)" \/>

If you still have a problem with it, there is something else wrong, probably in the RegEx.Match(mainPage, ItemPattern). According to the debugging you did, it sounds like the string is successfully being created, and there is no MatchCollection. So it's either in how you are obtaining the matches, or in referencing them.

edited Dec 16 '14 at 00:51

answered Dec 15 '14 at 22:57

peege

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It's not working :( Can you please enter this site http://rubular.com/ and enter
\n+
\n+\n+ as regular expression. And source code of this site http://www.vatanbilgisayar.com/cep-telefonu-modelleri/ as Test String. Than look at bottom of the page for match groups. When i try your solution in C# with this test string it does not match anything.
– Trax Dec 15 '14 at 23:22
title="(.*?)" \/>" ?? or title="(.*?)" /> – peege Dec 15 '14 at 23:27
\n+
\n+\n+ I'm writing exactly this to the first box in that site and left the second box empty
– Trax Dec 15 '14 at 23:31
It matched for me just now. I think the reason is that in your original post, you didn't write it exactly like that. it's the last three characters. I'll revise the code above. see my last comment to see where the difference is exactly. – peege Dec 15 '14 at 23:33
Still can't match anything. I edited the code in my question respect to your pattern. I'm using that code and still can't match aything. I really don't understand why this is not working. Maybe i should give up parsing html with regex. – Trax Dec 15 '14 at 23:44
All I can say about my answer, is that the string will get created as you laid out, and I tested on rubular.com with the source code you mentioned and got a match. There's something else going on. Have you tried stepping through the code as it executes and watching your Locals window, if you have one? – peege Dec 15 '14 at 23:47
Just checked as you say and can't find any problem. It doesn't match anything. Matchcollection is empty. – Trax Dec 15 '14 at 23:59

C# Regex Can't Match Anything (Probably because can't escape characters properly)

2 Answers2