How do I replace the first occurrence of a Substring in .NET?

Question

I am having string variable as follow

 string pctSign = "\0\0\0";

I want to replace first two characters with "%"

i.e. Final o/p:- pctSign="%\0\0";

How to do this with String.Replace?

Try using `Substring` (possibly in combination with `IndexOf`) instead. — Chris Sinclair, Sep 11 '12 at 11:18
possible duplicate of [How do I replace the *first instance* of a string in .NET?](http://stackoverflow.com/questions/141045/how-do-i-replace-the-first-instance-of-a-string-in-net) — Paolo Moretti, Sep 11 '12 at 11:20

Dennis Traub · Accepted Answer · 2012-09-11T11:37:25.323

5

// Option 1
var result = "%" + pctSign.Remove(0, 2);

// Option 2
var result = "%" + pctSign.Substring(2);

// Option 3
var regex = new Regex("^\\0");
var result = regex.Replace(pctSign, "%");

If you absolutely want to user String.Replace() then you can write your own extension method:

public static class StringExtension
{
    public static String Replace(this string self, 
                                      string oldString, string newString, 
                                      bool firstOccurrenceOnly = false)
    {
        if ( !firstOccurrenceOnly )
            return self.Replace(oldString, newString);

        int pos = self.IndexOf(oldString);
        if ( pos < 0 )
            return self;

        return self.Substring(0, pos) + newString 
               + self.Substring(pos + oldString.Length);
    }
}

// Usage:
var result = pctSign.Replace("/0", "%", true);

edited Sep 11 '12 at 11:37

answered Sep 11 '12 at 11:20

Dennis Traub

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isn't there any way to write this using Replace? – Amol Kolekar Sep 11 '12 at 11:28
1

@AmolKolekar there are two overloads for `String.Replace()` both of which replace **all** occurrences of the given string or char. String doesn't provide a `Replace` method that only replaces a specific occurrence. – Dennis Traub Sep 11 '12 at 11:31
Updated my answer and added a way to use `String.Replace` anyway. – Dennis Traub Sep 11 '12 at 11:37
I got simple solution here..http://stackoverflow.com/questions/5990093/how-to-change-nth-element-of-the-string – Amol Kolekar Sep 11 '12 at 13:34

score 2 · Answer 2 · answered Sep 11 '12 at 11:21

2

Try this:

var pctSign = "\0\0\0";
var result = string.Format("%{0}", pctSign.Substring(2));

answered Sep 11 '12 at 11:21

Spontifixus

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score 0 · Answer 3 · answered Sep 11 '12 at 11:20

0

string s = pctSign.Substring(2, pctSign.Length);
s = "%" + s;

answered Sep 11 '12 at 11:20

Roshana

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15

dnyan86 · Answer 4 · 2012-09-13T08:25:47.657

0

you mean only first two then

pctSign = "%"+pctSign.substring(2);

edited Sep 13 '12 at 08:25

answered Sep 11 '12 at 11:22

dnyan86

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1

This will remove all occurrences of `/0` because this is what `pctSign.substring(0,2)` evaluates to. – Dennis Traub Sep 11 '12 at 11:24

How do I replace the first occurrence of a Substring in .NET?

4 Answers4