How do I truncate a .NET string?

Question

I would like to truncate a string such that its length is not longer than a given value. I am writing to a database table and want to ensure that the values I write meet the constraint of the column's datatype.

For instance, it would be nice if I could write the following:

string NormalizeLength(string value, int maxLength) { return value.Substring(0, maxLength); }

Unfortunately, this raises an exception because maxLength generally exceeds the boundaries of the string value. Of course, I could write a function like the following, but I was hoping that something like this already exists.

string NormalizeLength(string value, int maxLength) { return value.Length <= maxLength ? value : value.Substring(0, maxLength); }

Where is the elusive API that performs this task? Is there one?

For the record, strings are immutable you can't truncate them you can only return a truncated copy of them. Nitpicky, I know. — John Weldon
– John Weldon, Commented May 5, 2010 at 20:55
@John Weldon: That's probably why the member function doesn't exist -- it doesn't follow the semantics of the datatype. On a side note, StringBuilder lets you truncate by shorterning the length, but you still need to perform the length check to avoid widening the string. — Steve Guidi
– Steve Guidi, Commented May 5, 2010 at 20:59
Whichever solution you pick, be sure to add a check for a null string before calling Substring or accessing the Length property. — Ray
– Ray, Commented May 5, 2010 at 20:59
@SteveGuidi - If that were the case, then there wouldn't be functions like Trim or Replace, which face similar semantic problems — Chris Rogers
– Chris Rogers, Commented Aug 3, 2016 at 23:20
@JohnWeldon More nitpicky than Microsoft themselves consistently are, as it happens - they're happy to document, for instance, .Trim() in a manner that makes it misleadingly sound like it mutates the string: "Removes all leading and trailing white-space characters from the current String object." — Mark Amery
– Mark Amery, Commented Jan 13, 2018 at 21:41

Edward Brey · Accepted Answer · 2020-08-19 19:56:25Z

You can create a Truncate extension method that compares the max length relative to the string length and calls Substring if needed.

If you want null handling behavior that parallels that of Substring, don't include a null check. That way, just as str.Substring(0, 10) throws a NullReferenceException if str is null, so will str.Truncate(10).

public static class StringExtensions { public static string Truncate(this string value, int maxLength) => value.Length <= maxLength ? value : value.Substring(0, maxLength); }

Jeremy · Accepted Answer · 2024-09-04 14:59:45Z

Old question, but I think there are new answers.

If you are using c# 6, (.net 4.6) you could do it like this, with a null conditional operator to make it concise:

public static string Truncate(this string input, int maxLength) { return input?.Substring(0, Math.Min(input.Length, maxLength)); }

If you are using c# 8 (.net core 3, .net standard 2.1, .net 5+) you can use the range operator. It is more concise but I personally think it is a bit less readable.

public static string Truncate(this string input, int maxLength) { return input?[..Math.Min(input.Length, maxLength)]; }

Raymond Osterbrink · Accepted Answer · 2018-11-15 12:45:47Z

As an addition to the possibilities discussed above I'd like to share my solution. It's an extension method that allows null (returns string.Empty) also there is a second .Truncate() for using it with an ellipsis. Beware, it's not performance optimized.

public static string Truncate(this string value, int maxLength) => (value ?? string.Empty).Substring(0, (value?.Length ?? 0) <= (maxLength < 0 ? 0 : maxLength) ? (value?.Length ?? 0) : (maxLength < 0 ? 0 : maxLength)); public static string Truncate(this string value, int maxLength, string ellipsis) => string.Concat(value.Truncate(maxLength - (((value?.Length ?? 0) > maxLength ? ellipsis : null)?.Length ?? 0)), ((value?.Length ?? 0) > maxLength ? ellipsis : null)).Truncate(maxLength);

Nae · Accepted Answer · 2020-12-23 22:48:55Z

Based on this, and this, here are two versions that will work for negative values of 'up to' values as well. This first one doesn't allow negative values silently by capping at 0:

public static string Truncate(this string value, int maxLength) { return string.IsNullOrEmpty(value) ? value : value.Substring(0, Math.Max(0, Math.Min(value.Length, maxLength))); }

This one goes in circle:

private static int Mod(this int a, int n) => (((a %= n) < 0) ? n : 0) + a; public static string Truncate(this string value, int maxLength) { return string.IsNullOrEmpty(value) ? value : value.Substring(0, maxLength.Mod(value.Length)); }

stefan.seeland · Accepted Answer · 2024-08-15 12:07:42Z

This code defines an extension method called UnicodeSafeTruncate that truncates a string to a specified maximum length while ensuring that it doesn't break any Unicode codepoints, such as emoji, accents, or other complex characters.

public static string UnicodeSafeTruncate(this string value, int maxLength) { if (value.Length <= maxLength) { return value; } var builder = new StringBuilder(); var builderForward = new StringBuilder(); var textElementEnumerator = StringInfo.GetTextElementEnumerator(value); while (textElementEnumerator.MoveNext()) { builderForward.Append(textElementEnumerator.Current); if (builderForward.ToString().Length > maxLength) { return builder.ToString(); } builder.Append(textElementEnumerator.Current); } return value; } public static void Main() { var value = "a👩🏽‍🚒👩🏽‍🚒b"; Console.WriteLine($"Input value: {value} (Length {value.Length})"); // Input value: a👩🏽‍🚒👩🏽‍🚒b (Length 16) var maxLength = 10; var brokenUnicode = value.Substring(0, maxLength); Console.WriteLine($"Substring Outcome: {brokenUnicode}"); // Substring Outcome: a👩🏽‍🚒👩 var actualTruncatedString = value.UnicodeSafeTruncate(maxLength); Console.WriteLine($"UnicodeSafeTruncate Outcome: {actualTruncatedString}"); // UnicodeSafeTruncate Outcome: a👩🏽‍🚒 }

TapiocaCom · Accepted Answer · 2013-05-17 20:19:21Z

-1

public static string Truncate( this string value, int maxLength ) { if (string.IsNullOrEmpty(value)) { return value; } return new string(value.Take(maxLength).ToArray());// use LINQ and be happy }

answered May 17, 2013 at 20:19

TapiocaCom

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1 Comment

Mark Amery Over a year ago

The ToArray() call here is just needless overhead; using e.g. String.Concat you can construct a string from an enumerable of characters without having to go via an array.

Sud · Accepted Answer · 2016-01-25 09:23:15Z

TruncateString

public static string _TruncateString(string input, int charaterlimit) { int characterLimit = charaterlimit; string output = input; // Check if the string is longer than the allowed amount // otherwise do nothing if (output.Length > characterLimit && characterLimit > 0) { // cut the string down to the maximum number of characters output = output.Substring(0, characterLimit); // Check if the character right after the truncate point was a space // if not, we are in the middle of a word and need to remove the rest of it if (input.Substring(output.Length, 1) != " ") { int LastSpace = output.LastIndexOf(" "); // if we found a space then, cut back to that space if (LastSpace != -1) { output = output.Substring(0, LastSpace); } } // Finally, add the "..." output += "..."; } return output; }

Why do you precede your public method name with an underscore?
This code can also suffer from performance issues when used in code that is performance critical. Not only that but it also allocates more than it should with the checking. Now if it were modified to use spans then the performance of it would be improved.

Raúl Diego · Accepted Answer · 2024-11-20 11:49:23Z

Short answer (requires c#8):

string? NormalizeLength(string value, int maxLength) { return value?.PadRight(maxLength)[..maxLength].Trim(); }

V.T. · Accepted Answer · 2016-05-27 13:39:11Z

Truncate String

public static string TruncateText(string strText, int intLength) { if (!(string.IsNullOrEmpty(strText))) { // split the text. var words = strText.Split(' '); // calculate the number of words // based on the provided characters length // use an average of 7.6 chars per word. int wordLength = Convert.ToInt32(Math.Ceiling(intLength / 7.6)); // if the text is shorter than the length, // display the text without changing it. if (words.Length <= wordLength) return strText.Trim(); // put together a shorter text // based on the number of words return string.Join(" ", words.Take(wordLength)) + " ...".Trim(); } else { return ""; } }

This does not answer the OP's question. First, it should be a member function (although you have written it as an extension method). Second, the OP does not specify that the text has to be split and words have be truncated to approx. 7.6 chars per word.
7.6 is just a number. you can write any other number you wish. This happened to be an average English word length. I found it on google. Using split is just an easy way to break down the words by space. I don't think that you want to display a half word! So unless you loop through to find empty space which will require more code, this is an easy way to truncate a string and display full words. This will ensure you that a string is not longer then the given length and you won't have broken words.

user3390116 · Accepted Answer · 2017-07-13 06:04:35Z

-4

This is the code I usually use:

string getSubString(string value, int index, int length) { if (string.IsNullOrEmpty(value) || value.Length <= length) { return value; } System.Text.StringBuilder sb = new System.Text.StringBuilder(); for (int i = index; i < length; i++) { sb.AppendLine(value[i].ToString()); } return sb.ToString(); }

edited Jul 13, 2017 at 6:04

answered Sep 19, 2014 at 23:52

user3390116

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3 Comments

Steve Guidi Over a year ago

Please note that concatenating strings with += is an expensive operation, especially when rebuilding character by character. .NET strings are immutable, which means in this case, a new string is created each time in your loop.

Chris Marisic Over a year ago

@SteveGuidi strings are not immutable, they just masquerade as immutable. I wish strings were true immutable primitives so I could have string and string?, but alas they are not primitives.

user3390116 Over a year ago

You say expensive as if the performance cost is significant, I changed it to use stringBuilder but I find that with += is easier to see what's going on, I just wanted the OP to easily understand the code.

SethGoodluck · Accepted Answer · 2018-02-16 19:20:03Z

I'd Recommend using the substring method for the same effective functionality.

 // Gets first n characters. string subString = inputString.Substring(0, n);

This has the benefit of letting you splice your string from either side or even somewhere in the middle without writing additional methods. Hope that helps :)

For additional reference: https://www.dotnetperls.com/substring

If your string is smaller than n it will fail. The point of truncate is to prevent that.

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