string.replace is not working

Question

I have function which accepts string (which is basically a XML doc). I am making this change:

  if (filterXml.Contains("&"))
    {
        filterXml.Replace("&", "&amp;");
    }

It is hitting this condition but not replacing the

 & to &amp;

What is wrong here?

[Similar questions](http://stackoverflow.com/questions/894905/how-to-replace-occurrences-of-with-an-empty-string) — Cemo, Oct 03 '11 at 18:26

Babak Naffas · Answer 1 · 2011-10-03T18:48:34.590

13

Remember, strings are immutable. So you have to assign the return value of the Replace method (notice that it returns a String object) back to your variable.

  if (filterXml.Contains("&"))
  {
      filterXml = filterXml.Replace("&", "&amp;");
  }

If you're doing a lot of work with String objects, make sure to read the the String reference page

edited Oct 03 '11 at 18:48

answered Oct 03 '11 at 18:21

Babak Naffas

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score 7 · Accepted Answer · answered Oct 03 '11 at 18:21

7

You need to save the result:

filterXml = filterXml.Replace("&", "&amp;");

but I would recommend encoding ALL special XML characters.

answered Oct 03 '11 at 18:21

Jared Peless

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Because strings are immutable. They don't change. They can't change. They won't change. Replace and similar methods don't change the string, they return a new, different string with the change applied. – phoog Oct 03 '11 at 18:27
@phoog The SHOULDN'T change. Quite different :-) Try looking at the StringBuilder.ToString of C# 2.0 with IlSpy and follow the string.InternalCopy :-) – xanatos Oct 03 '11 at 18:36

score 6 · Answer 3 · answered Oct 03 '11 at 18:23

6

You don't even need to do the Contains check. Just do the following:

filterXml = filterXml.Replace("&", "&amp;");

If there aren't any ampersands in the string, then nothing will change.

answered Oct 03 '11 at 18:23

DJ Quimby

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ipr101 · Answer 4 · 2011-10-03T18:29:18.223

4

Try -

  if (filterXml.Contains("&"))
    {
        filterXml = filterXml.Replace("&", "&amp;");
    }

Strings are immutable in .net, so the replace function returns a new string rather than altering the string it is called on. You are able to assign the altered result to the variable that contained your original string value.

edited Oct 03 '11 at 18:29

answered Oct 03 '11 at 18:21

ipr101

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score 1 · Answer 5 · answered Oct 03 '11 at 18:22

1

  if (filterXml.Contains("&"))
    {
        filterXml = filterXml.Replace("&", "&amp;");
    }

answered Oct 03 '11 at 18:22

AndrewC

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string.replace is not working

5 Answers5