using substring properly on a stringbuilder type

Question

I am building up a string of data using substring. The format of the data I want is

[1,2,3,4,5,6,7,8,9,10]

So I am building it up as follows

StringBuilder sb = new StringBuilder();
sb.append("1,");
sb.append("2,");
sb.append("3,");
.
.
.

The problem I run into is when I want to trim the final , before adding the closing ].

I could do

sb.ToString();
sb.Substring(0, (sb.Length - 1));
sb += "]";

But using the += is not very efficient as this creates a new string. Is there a better way of doing this?

`var result = string.Concat("[", string.Join(",", someEnumerable), "]");` is a little faster, and much simpler than a `StringBuilder` approach, I've tested it. — Jodrell, Nov 16 '12 at 12:15

L.B · Answer 1 · 2012-11-12T10:16:46.020

6

var str = "[" + String.Join(", ",Enumerable.Range(1,10)) + "]";

edited Nov 12 '12 at 10:16

answered Nov 12 '12 at 10:11

L.B

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But it's not what OP has asked for since it creates new strings and it's also not clear that OP wants only integers between 1 and 10 even if it's the sample data. – Tim Schmelter Nov 12 '12 at 10:15
1

Thanks for this, I never knew you could do this with link. It would require a re write of my code so i won't use it now, but it is good for the future @L.B – Wesley Skeen Nov 12 '12 at 10:28
I like this approach even if it is not particularly performance worthy due to the creation of several strings. – Matthew Layton Nov 12 '12 at 10:28
@WesleySkeen, you can do it in one line without linq of course, just use `String.Format`, as in my answer. – Jodrell Nov 12 '12 at 10:32

score 4 · Answer 2 · answered Nov 12 '12 at 10:12

4

Don't add the final , if you don't need it:

var sb = new StringBuilder().Append('[');
var first = true;
foreach (var item in collection)
{
    if (first)
        first = false;
    else
        sb.Append(',');
    sb.Append(item);
}
sb.Append(']');
var result = sb.ToString();

answered Nov 12 '12 at 10:12

dtb

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This is the most correct suggestion but the wrong code. You have to check for last one, not the first. – Sedat Kapanoglu Nov 12 '12 at 10:20
@ssg: I add a comma before each element except for the first one. Why is that wrong? – dtb Nov 12 '12 at 10:22
@dtb I thought you added comma after, sorry my bad. Then this is the proper answer. – Sedat Kapanoglu Nov 12 '12 at 10:24
@dtb this is the right answer. Sorry for my wrong initial interpretation :) +1ed :) – nawfal Nov 12 '12 at 10:40
`string.Format("[{0}]", string.Join(",", collection));` achieves the same in one line. – Jodrell Nov 12 '12 at 10:41
@Jodrell: Sure. But it creates a bunch of intermediate strings. That's not bad. Except if you want to avoid them. So I've proposed a solution that avoids any intermediate string. – dtb Nov 12 '12 at 10:43
@dtd, is that how `String.Join` and `String.Format` are implemented? Its more sophisticated than that, http://stackoverflow.com/questions/585860/string-join-vs-stringbuilder-which-is-faster – Jodrell Nov 12 '12 at 10:48
I did a little test, if performance really matters, this method using the `StringBuilder` directly is a little faster. I think this must be because the Join-Format method has to allocate and populate the memory twice. +1 – Jodrell Nov 12 '12 at 14:23
@dtb, I did a little more testing and found a `Concat` and `Join` combination is actually faster than `StringBuilder`. – Jodrell Nov 16 '12 at 12:11

score 3 · Accepted Answer · answered Nov 12 '12 at 10:11

3

The easiest is to use -= on the StringBuilder's Length since it's writable:

sb.Length -= 1; // removes the last char

answered Nov 12 '12 at 10:11

Tim Schmelter

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Wasn't the question about the `+=`? – Jodrell Nov 12 '12 at 10:17
1

@Jodrell: I'm not sure because the title mentions "using substrings properly" and "The problem I run into is when I want to trim the final , before adding the closing ]". – Tim Schmelter Nov 12 '12 at 10:18
This may need a check if `"[]"` is a valid result. Otherwise the opening bracket might get removed. – dtb Nov 12 '12 at 10:18
@dtb: Of course this needs an additonal check `if(sb.Length>1)sb.Length -= 1;` before appending the final `]`. – Tim Schmelter Nov 12 '12 at 10:21
1

Setting `.Length` copies the contents of StringBuilder buffer to another newly created array, it's not much different than `Substring` approach so definitely not efficient. Try @dtb 's answer. – Sedat Kapanoglu Nov 12 '12 at 10:36
1

@ssg: Only if the buffer is not large enough for the new length. Which is not the case if the length is decreased. – dtb Nov 12 '12 at 10:40

score 3 · Answer 4 · edited May 23 '17 at 12:18

3

UPDATE

After a little testing

var result = string.Concat("[", string.Join(",", someEnumerable), "]");

is both much simpler and faster than a builder approach

You could always just do

var result = string.Format("[{0}]", string.Join(",", someEnumerable));

The sequence can be anything you want, for instance

var someEnumerable = Enumerable.Range(1, 10);

This seems simpler than reinventing the wheel, and avoids intermediate strings.

This does make assumptions about the implementation of String.Join but, I think you should assume that its good enough for this purpose.

For more information, this Question does a comparison between String.Join and StringBuilder.

This Question indicates that String.Format uses a StringBuilder.

edited May 23 '17 at 12:18

Community

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answered Nov 12 '12 at 10:12

Jodrell

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Whilst it was not me that downvoted, the code does not work. It should be string.Join(",", someEnumerable)); – Matthew Layton Nov 12 '12 at 10:32
1

Also I do not know if this is creating multiple strings behind the scenes. – Matthew Layton Nov 12 '12 at 10:32
@activwerx, doh, fixed the ommited parameter. You are right, I don't know how `String.Join` is implemented either but, I should assume that its has been provided for a reason. – Jodrell Nov 12 '12 at 10:36
Well I've removed the downvote as I think this is a good implementation! :-) – Matthew Layton Nov 12 '12 at 10:36
`Any comments downvoters?` that sounded so audacious when you know it why you were. Editing a wrong answer and then questioning back masks nothing. SO is so transparent. While I was one downvoter, I removed it now. – nawfal Nov 12 '12 at 10:43
@nawfal I can't catch the exceptions unless they are thrown. I grant that the answer as evolved somewhat but, thats the idea, right? – Jodrell Nov 12 '12 at 10:46
@Jodrell yes thats alright. The way you phrased it made it look like you're so sure there's nothing wrong with your answer :) – nawfal Nov 12 '12 at 11:03

Matthew Layton · Answer 5 · 2012-11-12T10:33:51.463

Here is an example as a nice clean method:

    public static string WriteValues(int start, int end)
    {
        StringBuilder sb = new StringBuilder();
        sb.Append("[");
        for (int index = start; index <= end; index++)
        {
            sb.Append(index).Append(",");
        }
        sb.Length -= 1;
        sb.Append("]");
        return sb.ToString();
    }

This does all the work in the StringBuilder and then passes back a single string. Also you can specify the start and end values!

using substring properly on a stringbuilder type

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