How to handle multiple regular expression in same string C#

Question

I'm trying to handel multiple different situation in the same string with regular expression. But when i'm using the code under, only the last expression will work. so dobbel stars(**) will be posted like it is, but underline(_) will be handled by the replace()function.

[HttpPost]
[ValidateInput(false)]
 public ActionResult Comment(Models.CommentModel s)
    {
        Regex fat = new Regex(@"\*\*(.*?)\*\*");
        Regex italic = new Regex(@"_(.*?)_");

       s.comment = fat.Replace(HttpUtility.HtmlEncode(s.comment), "<b>$1</b>");
       s.comment = italic.Replace(HttpUtility.HtmlEncode(s.comment), "<i>$1</i>");

       var db = new WebApplication1.Models.ApplicationDbContext();

        if (ModelState.IsValid)
        {

            if (file != null)
        {
            db.Comments.Add(s);
            db.SaveChanges();
            return RedirectToAction("Comment");
        }
        return View(s);
    }

To decrease the amount of code I have tried to merge italicand fatstring together like this: Regex(@"\*\*(.*?)\*\*|_(.*?)_"); but then i have another problem, how can Regex know the difference?

stackoverflow.com/questions/1732348/… Why are you trying to parse html with regex? — Eser
– Eser, Commented Apr 28, 2016 at 20:05

Xiaoy312 · Accepted Answer · 2016-04-28 20:37:43Z

1

Because you are encoding the same html twice :

   // comment : sampletext **bold** _italic_ stuffsss

   s.comment = fat.Replace(HttpUtility.HtmlEncode(s.comment), "<b>$1</b>");
   // comment : sampletext <b>bold</b> _italic_ stuffsss

   s.comment = italic.Replace(HttpUtility.HtmlEncode(s.comment), "<i>$1</i>");
   // comment : sampletext &lt;b&gt;bold&lt;/b&gt; <i>italic</i> stuffsss

Simply encoding it once, when you are done with the replacing :

Regex fat = new Regex(@"\*\*(.*?)\*\*"); // btw this is called `bold` not `fat`
Regex italic = new Regex(@"_(.*?)_");

s.comment = HttpUtility.HtmlEncode(s.comment)

s.comment = fat.Replace(s.comment, "<b>$1</b>");
s.comment = italic.Replace(s.comment, "<i>$1</i>");

edited Apr 28, 2016 at 20:37

answered Apr 28, 2016 at 20:18

Xiaoy312

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2 Comments

elektronet Over a year ago

thank you this worked perfectly, the only change i had to make were the last line, it needed to be above the replace() lines to work.

Xiaoy312 Over a year ago

you are right. Indeed, it has to be above the replace, as any angle-bracket will be encoding which is not what we want.

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