How does the string replace function in VB.net not work?

Question

I wrote up some code. The code is shown below. The first part is to read a html into string format. The second part is to search a mark in the string and replace the string by other string.

The 1st part (I test it many times, it works fine)

Public Function ReadTextFile(ByVal TextFileName As String) As String
    Dim TempString As String
    Dim StreamToDisplay As StreamReader
    StreamToDisplay = New StreamReader(TextFileName)
    TempString = StreamToDisplay.ReadToEnd
    StreamToDisplay.Close()
    Return TempString
End Function

The 2nd part (I test it many times, the search and replace does not work. I checked many times that the "TempText" DOES contain string. The "the_key_string" DOES inside the "TempText" String. I check it by using QuickWatch in VB.net. However, the replace function does NOT do its job)

            Dim TextPath = C:xxxxxx
            TempText = ReadTextFile(TextPath)
            TempText.Replace("the_key_string", "replace_by_this_string")

Please help. I have no clue where I made the mistake

Strings are immutable, you need to re-assign TempText from the result of Replace. — vcsjones
– vcsjones, Commented Oct 7, 2013 at 20:42

MarcinJuraszek · Accepted Answer · 2013-10-07 20:42:52Z

16

String.Replace returns new string instead of modifying the source one. You have to assign it back to your variable:

TempText = TempText.Replace("the_key_string", "replace_by_this_string")

From MSDN:

Returns a new string in which all occurrences of a specified string in the current instance are replaced with another specified string.

answered Oct 7, 2013 at 20:42

MarcinJuraszek

126k15 gold badges199 silver badges267 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Tim Schmelter · Accepted Answer · 2013-10-07 20:48:31Z

5

Strings are immutable, that means once they are created you cannot modify them. So you have to create a new one and assign that to your string variable:

TempText = TempText.Replace("the_key_string", "replace_by_this_string")

MSDN: String Data Type (Visual Basic):

Once you assign a string to a String variable, that string is immutable, which means you cannot change its length or contents. When you alter a string in any way, Visual Basic creates a new string and abandons the previous one. The String variable then points to the new string.

edited Oct 7, 2013 at 20:48

answered Oct 7, 2013 at 20:43

Tim Schmelter

462k79 gold badges719 silver badges980 bronze badges

Comments

Jonathan Bates · Accepted Answer · 2013-10-07 20:42:57Z

2

You have to assign the value to something, like :

TempText = TempText.Replace("the_key_string", "replace_by_this_string")

answered Oct 7, 2013 at 20:42

Jonathan Bates

1,83514 silver badges22 bronze badges

Comments

David · Accepted Answer · 2013-10-07 20:43:08Z

2

This is performing the string replace, but it's not putting the result of it anywhere:

TempText.Replace("the_key_string", "replace_by_this_string")

You need to assign the result to something:

TempText = TempText.Replace("the_key_string", "replace_by_this_string")

answered Oct 7, 2013 at 20:43

David

221k42 gold badges245 silver badges337 bronze badges

Comments

ChrisW · Accepted Answer · 2013-10-07 20:43:59Z

0

The Replace method returns the modified string.

You need something like this:

Dim TextPath = C:xxxxxx
TempText = ReadTextFile(TextPath)
Dim ModifiedString as String
ModifiedString = TempText.Replace("the_key_string", "replace_by_this_string")

answered Oct 7, 2013 at 20:43

ChrisW

9,4392 gold badges22 silver badges35 bronze badges

Comments

int3 · Accepted Answer · 2013-10-07 20:46:45Z

0

"this is a string" If you do Replace 'string' with 'whatever' this string should be: "this is a whatever". so what you can do is put that in a new string. how? replace method returns a string so, it is easy :) see this: msdn

answered Oct 7, 2013 at 20:46

int3

6581 gold badge6 silver badges21 bronze badges

Comments

R2D2 · Accepted Answer · 2022-04-22 16:07:22Z

0

try these and one might work. i think that it is the underscore.

TempText.Replace("thekeystring", "replace_by_this_string")

TempText.Replace("the key string", "replace_by_this_string")

TempText.Replace("the__key__string", "replace_by_this_string")

answered Apr 22, 2022 at 16:07

R2D2

711 silver badge10 bronze badges

Comments

spinjector · Accepted Answer · 2024-11-08 02:03:22Z

0

something came to my mind as I was reading this. As readers should understand after reading this post, String.Replace is a function, not a statement. However, StringBuilder.Replace() is a statement.

Thus, to use the poster's code snippet as a model, the following would work...

    Dim sb As System.Text.StringBuilder
    sb = New System.Text.StringBuilder("Hello, the_key_string!")
    sb.Replace("the_key_string", "replace_by_this_string")
    MsgBox(sb.ToString)

Also, depending on circumstances, StringBuilder may be more efficient & faster than String.

answered Nov 8, 2024 at 2:03

spinjector

3,6984 gold badges35 silver badges71 bronze badges

Collectives™ on Stack Overflow

How does the string replace function in VB.net not work?

8 Answers 8

Comments

Comments

Comments

Comments

Comments

Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

8 Answers 8

Comments

Comments

Comments

Comments

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related