How to truncate or pad a string to a fixed length in c#

Question

Is there a one-liner way of setting a string to a fixed length (in C#), either by truncating it or padding it with spaces (' ').

For example:

string s1 = "abcdef";
string s2 = "abc";

after setting both to length 5, we should have:

"abcde"
"abc  "

https://msdn.microsoft.com/en-us/library/system.string.format.aspx ?? — Ingenioushax, Mar 29 '17 at 14:47

score 39 · Accepted Answer · answered Mar 29 '17 at 14:57

39

All you need is PadRight followed by Substring (providing that source is not null):

string source = ...
int length = 5;

string result = source.PadRight(length).Substring(0, length);

In case source can be null:

string result = source == null 
  ? new string(' ', length) 
  : source.PadRight(length).Substring(0, length);

answered Mar 29 '17 at 14:57

Dmitry Bychenko

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in the context of .net6, is the `.Substring(0, length)` needed for spaces? – rhavelka Apr 27 '22 at 14:21
2

@rhavelka: `PadRight(length)` guarantees that we have *at least* `length` length then `Substring(0, length)` guarantees that we have *at most* `length` length; so far so good we have exactly `length` length – Dmitry Bychenko Apr 27 '22 at 14:32

score 5 · Answer 2 · edited Mar 29 '17 at 14:57

5

private string fixedLength(string input, int length){
    if(input.Length > length)
        return input.Substring(0,length);
    else
        return input.PadRight(length, ' ');
}

edited Mar 29 '17 at 14:57

huMpty duMpty

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answered Mar 29 '17 at 14:51

waka

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I was hoping for a one-liner - but suspected I would have to resort to this – Graham Mar 29 '17 at 14:52
`s1.Length > 5 ? s1.Substring(0,5) : s1.PadRight(5)` will have to do – Graham Mar 29 '17 at 14:56
@Graham was just going to suggest you make use of ternary operators, then. But it makes the code more ugly, imo. – waka Mar 29 '17 at 14:57
2

@Graham: Make it a extension method will work better for this case – huMpty duMpty Mar 29 '17 at 14:57

Reinstate Monica · Answer 3 · 2020-10-13T07:17:38.963

2

(This answer previously contained incorrect code, as referenced in the comments.)

A custom one-liner would be str.Length > 5 ? str.Substring(0,5) : str.PadRight(5);.

edited Oct 13 '20 at 07:17

answered Nov 11 '17 at 18:20

Reinstate Monica

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Did you test the custom one-liner with a LONGER string, that needs to be truncated? Also, PadRight should be given *the total desired length*, not the number of blanks to add. – ToolmakerSteve Dec 04 '18 at 13:42
@ToolmakerSteve the one-liner tests str.Length and truncates it using Substring(); also the numeral 5 in PadRight *is* the desired length. That's exactly what was asked for in the question. Have I misunderstood something? – Reinstate Monica Oct 10 '20 at 21:30
I see that you edited the answer after my comment. The one-liner looks correct now. Unfortunately, the format string is obviously wrong - no closing brace. More importantly, **that string format won't truncate a longer string, IIRC** - please test. (Someone else must have downvoted.) Either find a way to fix the string.format so it will truncate, or remove that part of the answer. – ToolmakerSteve Oct 12 '20 at 23:58
It looks like what you meant for the format string was "{0,-5}". That will PAD a shorter string to make it 5 characters, but will NOT TRUNCATE a longer string. In [String.Format doc](https://learn.microsoft.com/en-us/dotnet/api/system.string.format?view=netcore-3.1): "If the value of alignment is less than the length of the argument to be inserted, alignment is ignored ..." I don't see any format specification in the docs, that is capable of string truncation. (A number AFTER the **":"**, like you did, is not valid, AFAIK. A letter representing a formatting code is expected there.) – ToolmakerSteve Oct 13 '20 at 00:40
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@ToolmakerSteve Oops! I had thought your comment was new (the answer showed up in my inbox) and I didn't check the date, sorry about that. I can't figure out what I was thinking about the Format() call - will erase. – Reinstate Monica Oct 13 '20 at 07:16

score 2 · Answer 4 · answered Jan 04 '22 at 20:47

2

I would use the @waka answer, but as an extension method and null verification, like this:

    public static string FixedLength(this string value, int totalWidth, char paddingChar)
    {
        if (value is null)
            return new string(paddingChar, totalWidth);

        if (value.Length > totalWidth)
            return value.Substring(0, totalWidth);
        else
            return value.PadRight(totalWidth, paddingChar);
    }

answered Jan 04 '22 at 20:47

Jhonnatan Panoch

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This does not provide an answer to the question. Once you have sufficient [reputation](https://stackoverflow.com/help/whats-reputation) you will be able to [comment on any post](https://stackoverflow.com/help/privileges/comment); instead, [provide answers that don't require clarification from the asker](https://meta.stackexchange.com/questions/214173/why-do-i-need-50-reputation-to-comment-what-can-i-do-instead). - [From Review](/review/late-answers/30739098) – Jan 07 '22 at 23:22

score 1 · Answer 5 · answered Mar 29 '17 at 14:51

1

Have you tried s1.PadLeft(5);

you can also specify the character for padding if you want something else than spaces

s1.PadLeft(6, '.');

Would give you: "abcdef."

to do both:

var s1 = "1234567890";
var s2 = s1.SubString(5).PadLeft(5);

answered Mar 29 '17 at 14:51

Lorien

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Sorry, but `s1.SubString(5).PadLeft(5);` is `67890`; and *exception* if `s1 = "123"` – Dmitry Bychenko Mar 29 '17 at 15:05

score 1 · Answer 6 · answered Nov 09 '22 at 21:53

1

This will always produce a string with <= maxWidth characters

public static string MaxLength(this string value, int maxWidth)
{
  return (value == null) ?
  String.Empty :
  value.PadRight(maxWidth).Substring(0, maxWidth).TrimEnd();
}

answered Nov 09 '22 at 21:53

Derek Wade

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How to truncate or pad a string to a fixed length in c#

6 Answers6