How do I replace part of a string in C#?

Question

Supposed I have the following string:

string str = \"text\";

And I would like to change \'tag\' to \'newTag\' so the

Answer 1

string str = "<tag>text</tag>";
string newValue = new XElement("newTag", XElement.Parse(str).Value).ToString();

Answer 2

To make it optional, simply add a "?" AFTER THE "/", LIKE THIS:

<[/?]*tag>

Answer 3

var input = "<tag>text</tag>";
var result = Regex.Replace(input, "(</?).*?(>)", "$1newtag$2");

Answer 4

Why use regex when you can do:

string newstr = str.Replace("tag", "newtag");

or

string newstr = str.Replace("<tag>","<newtag>").Replace("</tag>","</newtag>");

Edited to @RaYell's comment

Answer 5

Your most basic regex could read something like:

// find '<', find an optional '/', take all chars until the next '>' and call it
//   tagname, then take '>'.
<(/?)(?<tagname>[^>]*)>

If you need to match every tag.

---

Or use positive lookahead like:

<(/?)(?=(tag|othertag))(?<tagname>[^>]*)>

if you only want tag and othertag tags.

---

Then iterate through all the matches:

string str = "<tag>hoi</tag><tag>second</tag><sometag>otherone</sometag>";

Regex matchTag = new Regex("<(/?)(?<tagname>[^>]*)>");
foreach (Match m in matchTag.Matches(str))
{
    string tagname = m.Groups["tagname"].Value;
    str = str.Replace(m.Value, m.Value.Replace(tagname, "new" + tagname));
}