Re: Why does this not change my string? - C# Discussion Boards

15-Aug-11 11:44

Hello.

I took this small function from anouther project, and I slightly modified it to work with a string object.

It accepts a string, and it should add a '-' for every nth charicture, as set by the code.

private void encodeString(string input)
        {
           
            for (int i = 0; i < input.Length-1; i++)
            {

                if ((i + 1) % 6 == 0)
                {
                    input.Insert(i, "-");

                }


            }

        }

It simply does not alter the string.

I simply want to pass string...

string test = ("00000000000000000000");

and end up with...

string test = ("00000-00000-00000-00000");

Thank you for any help with this.
Kind Regards,

Stephen

Dave Kreskowiak15-Aug-11 11:49

Dave Kreskowiak

15-Aug-11 11:49

Because Strings are immutable. That means once created, they cannot be changed.

You have to change this to either pass the string in by reference (you'll be returning a new string anyway) or change this so it returns a string. I prefer the latter...

A guide to posting questions on CodeProject[^]

Dave Kreskowiak

stephen.darling15-Aug-11 11:55

Re: Why does this not change my string? [modified]

15-Aug-11 11:55

Dave Kreskowiak wrote:
or change this so it returns a string

Sorry to ask, but how would I do that from within my function?

Steve

Dave Kreskowiak15-Aug-11 12:36

Dave Kreskowiak

15-Aug-11 12:36

Here's one way of doing it:

private string encodeString(string input)
{
    StringBuilder buffer = new StringBuilder();
    buffer.AppendFormat("{0}-{1}-{2}-{3}",
                input.SubString(0, 5),
                input.SubString(5, 5),
                input.SubString(10, 5),
                input.SubString(15, 5));

    return buffer.ToString();        
}

A guide to posting questions on CodeProject[^]

Dave Kreskowiak

modified on Tuesday, August 16, 2011 8:00 AM

stephen.darling15-Aug-11 12:41

15-Aug-11 12:41

Thank you,
Worked perfect!

Regards,
Stephen

Luc Pattyn15-Aug-11 11:50

15-Aug-11 11:50

stephen.darling wrote:
It simply does not alter the string.

strings are immutable, nothing you do in .NET will ever alter a string. At best you replace one string by another one, and that is exactly why string methods have a return value.

I suggest you choose an introductory book to C# and start studying it thoroughly, you seem to still be struggling with the basics of the language.

Smile | :)

Luc Pattyn [My Articles] Nil Volentibus Arduum

PIEBALDconsult15-Aug-11 15:28

15-Aug-11 15:28

(Pssst... Reflection.)

Luc Pattyn15-Aug-11 15:37

15-Aug-11 15:37

Luc wrote:
nothing you do in .NET will ever alter a string

"you" wasn't referring to you! Big Grin | :-D

And you really shouldn't.

Luc Pattyn [My Articles] Nil Volentibus Arduum

PIEBALDconsult15-Aug-11 15:41

15-Aug-11 15:41

"It's what I oughtn't to do, but I do anyway." -- Mel Brooks' History of the World Part 1

Luc Pattyn15-Aug-11 15:53

15-Aug-11 15:53

Very appropriately, it goes on: Will you convert? “No, no, no, no.” ref[^]

Smile | :)

Luc Pattyn [My Articles] Nil Volentibus Arduum

PIEBALDconsult15-Aug-11 16:01

15-Aug-11 16:01

You're passing Mel Brooks by reference? OMG | :OMG:

Luc Pattyn15-Aug-11 16:30

15-Aug-11 16:30

of course, there's too much value to pass on.

Smile | :)

Luc Pattyn [My Articles] Nil Volentibus Arduum

fcronin15-Aug-11 12:08

fcronin

15-Aug-11 12:08

private string encodeString(string input)
{
   string output = string.Empty;

   for (int i = 0; i < input.Length-1; i++)
   {
      if ((i + 1) % 6 == 0)
      {
         output = input.Insert(i, "-");
      }
   }

   return output;
}

stephen.darling15-Aug-11 12:14

15-Aug-11 12:14

Hello.

I tried your code, however, it produces the following result...

"38459171915879268-601"

So, it appears to be adding the whole string and then a '-', instead of a '-' every 5 charictures?

Thank you,
Stephen

fcronin16-Aug-11 2:39

fcronin

16-Aug-11 2:39

I apologize... I threw that in haste without really thinking it through... this is probably the easiest way to handle any length string...

static string encodeString(string input)
{
    string output = string.Empty;
    for (int i = 0; i < input.Length; i++)
    {
        output += input.Substring(i, 1);
        if ((i+1) % 6 == 0 && i != (input.Length-1))
            output += "-";
    }
    return output;
}

stephen.darling16-Aug-11 7:27

16-Aug-11 7:27

fcronin wrote:
I apologize... I threw that in haste without really thinking it through... this is probably the easiest way to handle any length string...

No problem!
Thank you again,

Steve

PIEBALDconsult15-Aug-11 15:30

Re: Why does this not change my string? [modified]

15-Aug-11 15:30

And you can increment i by six if you like; you're not limited to incrementing by one.

Shameel15-Aug-11 21:33

Shameel

15-Aug-11 21:33

stephen.darling wrote:
It simply does not alter the string.

And it will not, no matter what you do. As others have already pointed out, strings are immutable in .NET which means they cannot be altered once they're created.

Take a look at this example:

string a = "abc";
a = a + "xyz";

You might be thinking that in line 2 the characters "xyz" is appended to the string a, but that is not the case. When line 2 is executed, the Runtime creates a new string that is the result of the concatenation i.e. "abcxyz" and makes the variable a point to the new string. The old "abc" string becomes garbage (since it has no valid reference) and is collected during the next GC cycle.

To make large changes to to strings, it is recommended to use the System.Text.StringBuilder class.

private string encodeString(string input)
{
    StringBuilder builder = new StringBuilder();
    for (int i = 0; i < input.Length; i++) {
        builder.Append(input[i]);
        if ((i + 1) % 6 == 0) {
            builder.Append("-");
        }
    }
    return builder.ToString();
}

And use your method like this:

string input = "00000000000000000000";
string output = encodeString(input); //output contains "00000-00000-00000-00000"

modified on Tuesday, August 16, 2011 2:45 PM

Matt Meyer16-Aug-11 5:50

Matt Meyer

16-Aug-11 5:50

i < input.Length-1

I think you mean

i < input.Length

Otherwise you're dropping the last character.