String.Replace not replacing the string during runtime

Question

The following line in the below code doesn't cause any effect:

string1.Replace(string1.Substring(firstchar, lastchar - firstchar), "##");

string1 remains unchanged and I get the same index returned when using IndexOf.

while (firstchar != string1.LastIndexOf("test"))
{

    firstchar = string1.IndexOf("test");
    lastchar = string1.IndexOf(" ");
    using (StreamWriter writer = new StreamWriter("C:\\textfile1.txt"))
    {
        writer.WriteLine(string1.Substring(firstchar, lastchar - firstchar));
        writer.WriteLine();
        writer.Dispose();
    }
    string1.Replace(string1.Substring(firstchar, lastchar - firstchar), "##");

}

Note that there's no point in explicitly calling writer.Dispose() at the end of a using statement which will dispose it already. — Jon Skeet
– Jon Skeet, Commented Dec 2, 2010 at 9:28

Øyvind Bråthen · Accepted Answer · 2010-12-02 09:27:04Z

12

Change

string1.Replace(string1.Substring(firstchar, lastchar - firstchar), "##");

to

string1 = string1.Replace(string1.Substring(firstchar, lastchar - firstchar), "##");

string.Replace does not alter the original string, but returns the altered string as it's return value.

answered Dec 2, 2010 at 9:27

Øyvind Bråthen

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Comments

gpvos · Accepted Answer · 2010-12-02 09:30:01Z

7

string1 = string1.Replace(...);

From the docs: String.Replace returns a new string in which all occurrences of a specified string in the current instance are replaced with another specified string.

answered Dec 2, 2010 at 9:30

gpvos

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Comments

TalentTuner · Accepted Answer · 2010-12-02 09:30:12Z

2

Strings are immutatble so if you change in a string object , a new object is created so you need to have the reference of the newly created string.

so

string1 = string1.Replace(string1.Substring(firstchar, lastchar - firstchar), "##");

will solve the issue

answered Dec 2, 2010 at 9:30

TalentTuner

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Comments

Prasanna K Rao · Accepted Answer · 2010-12-02 09:54:11Z

1

Refer to this MSDN Documentation

Just as others said, you need to use the return value from the replace operation.

answered Dec 2, 2010 at 9:54

Prasanna K Rao

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Comments

Yudner · Accepted Answer · 2023-07-21 15:56:16Z

0

Indeed, you solve it by getting the value of "Replace".

I was doing the following:

string code = "A123BCD";
code.Replace("123", "R");

and expected to have "ARBCD", but it gave me the initial result.

But it was necessary to do:

code = code.Replace("123", "R");

and all good.

answered Jul 21, 2023 at 15:56

Yudner

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