Question

I’ve got a chunk of text in a StringBuilder object. I need to replace one substring with another. The StringBuilder Replace method can do this, but it replaces every instance of the substring and I only want to replace the first found instance. Is there a way to tell StringBuilder to only do one replace?

I’m sure I could code this up myself, I’m just wondering if there is a built in way to achieve this that I am currently missing.

Answer 1

Yes, but not directly. Two of the four overloads of Replace work on a substring of the StringBuilder contents, but you’ll need to find the position of the first occurrence for that to work.

Here’s the one you want:
http://msdn.microsoft.com/en-us/library/y1bxd041.aspx

Edit: Unfortunately, I don’t see a way to find the first occurrence without calling ToString on the StringBuilder.

(Sorry for the VB, I have a VB project open.)

Dim orig As String = "abcdefgabcdefg"
Dim search As String = "d"
Dim replace As String = "ZZZ"
Dim sb As New StringBuilder(orig)

Dim firstOccurrence = sb.ToString().IndexOf(search)

If firstOccurrence > -1 Then
    sb.Replace(search, replace, firstOccurrence, search.Length)
End If