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?

Answer 1

There isn't a Truncate() method on string, unfortunately. You have to write this kind of logic yourself. What you can do, however, is wrap this in an extension method so you don't have to duplicate it everywhere:

public static class StringExt
{
    public static string Truncate(this string value, int maxLength)
    {
        if (string.IsNullOrEmpty(value)) return value;
        return value.Length <= maxLength ? value : value.Substring(0, maxLength); 
    }
}

Now we can write:

var someString = "...";
someString = someString.Truncate(2);

2021-09-17 Alternative with suffix and c#8 nullable reference types.

public static class StringExt
{
    public static string? Truncate(this string? value, int maxLength, string truncationSuffix = "…")
    {
        return value?.Length > maxLength
            ? value.Substring(0, maxLength) + truncationSuffix
            : value;
    }
}

To write:

"abc".Truncate(2);          // "ab…"
"abc".Truncate(3);          // "abc"
((string)null).Truncate(3); // null

Answer 2

Or instead of the ternary operator, you could use Math.min

public static class StringExt
{
    public static string Truncate( this string value, int maxLength )
    {
        if (string.IsNullOrEmpty(value)) { return value; }

        return value.Substring(0, Math.Min(value.Length, maxLength));
    }
}

Answer 3

Because performance testing is fun: (using linqpad extension methods)

var val = string.Concat(Enumerable.Range(0, 50).Select(i => i % 10));

foreach(var limit in new[] { 10, 25, 44, 64 })
    new Perf<string> {
        { "newstring" + limit, n => new string(val.Take(limit).ToArray()) },
        { "concat" + limit, n => string.Concat(val.Take(limit)) },
        { "truncate" + limit, n => val.Substring(0, Math.Min(val.Length, limit)) },
        { "smart-trunc" + limit, n => val.Length <= limit ? val : val.Substring(0, limit) },
        { "stringbuilder" + limit, n => new StringBuilder(val, 0, Math.Min(val.Length, limit), limit).ToString() },
    }.Vs();

The truncate method was "significantly" faster. #microoptimization

Early

• truncate10 5788 ticks elapsed (0.5788 ms) [in 10K reps, 5.788E-05 ms per]
• smart-trunc10 8206 ticks elapsed (0.8206 ms) [in 10K reps, 8.206E-05 ms per]
• stringbuilder10 10557 ticks elapsed (1.0557 ms) [in 10K reps, 0.00010557 ms per]
• concat10 45495 ticks elapsed (4.5495 ms) [in 10K reps, 0.00045495 ms per]
• newstring10 72535 ticks elapsed (7.2535 ms) [in 10K reps, 0.00072535 ms per]

Late

• truncate44 8835 ticks elapsed (0.8835 ms) [in 10K reps, 8.835E-05 ms per]
• stringbuilder44 13106 ticks elapsed (1.3106 ms) [in 10K reps, 0.00013106 ms per]
• smart-trunc44 14821 ticks elapsed (1.4821 ms) [in 10K reps, 0.00014821 ms per]
• newstring44 144324 ticks elapsed (14.4324 ms) [in 10K reps, 0.00144324 ms per]
• concat44 174610 ticks elapsed (17.461 ms) [in 10K reps, 0.0017461 ms per]

Too Long

• smart-trunc64 6944 ticks elapsed (0.6944 ms) [in 10K reps, 6.944E-05 ms per]
• truncate64 7686 ticks elapsed (0.7686 ms) [in 10K reps, 7.686E-05 ms per]
• stringbuilder64 13314 ticks elapsed (1.3314 ms) [in 10K reps, 0.00013314 ms per]
• newstring64 177481 ticks elapsed (17.7481 ms) [in 10K reps, 0.00177481 ms per]
• concat64 241601 ticks elapsed (24.1601 ms) [in 10K reps, 0.00241601 ms per]

Answer 4

In .NET 4.0 you can use the Take method:

string.Concat(myString.Take(maxLength));

Not tested for efficiency!

Answer 5

I figured I would throw in my implementation since I believe it covers all of the cases that have been touched on by the others and does so in a concise way that is still readable.

public static string Truncate(this string value, int maxLength)
{
    if (!string.IsNullOrEmpty(value) && value.Length > maxLength)
    {
        return value.Substring(0, maxLength);
    }

    return value;
}

This solution mainly builds upon the Ray's solution and opens up the method for use as an extension method by using the this keyword just as LBushkin does in his solution.

Answer 6

Another solution:

return input.Substring(0, Math.Min(input.Length, maxLength));

Answer 7

You could use LINQ... it eliminates the need to check string length. Admittedly maybe not the most efficient, but it's fun.

string result = string.Join("", value.Take(maxLength)); // .NET 4 Join

or

string result = new string(value.Take(maxLength).ToArray());

Answer 8

I did mine in one line sort of like this

value = value.Length > 1000 ? value.Substring(0, 1000) : value;

Answer 9

In C# 8 the new Ranges feature can be used...

value = value[..Math.Min(30, value.Length)];

Answer 10

The .NET Framework has an API to truncate a string like this:

Microsoft.VisualBasic.Strings.Left(string, int);

But in a C# app you'll probably prefer to roll your own than taking a dependency on Microsoft.VisualBasic.dll, whose main raison d'etre is backwards compatibility.

Answer 11

Seems no one has posted this yet:

public static class StringExt
{
    public static string Truncate(this string s, int maxLength)
    {
        return s != null && s.Length > maxLength ? s.Substring(0, maxLength) : s;
    }
}

Using the && operator makes it marginally better than the accepted answer.

Answer 12

Here's a C# 9 one-liner:

public static string? Truncate(this string? value, int maxLength) => value is null or "" || value.Length <= maxLength ? value : value[..maxLength];

Answer 13

I know this is an old question, but here is a nice solution:

public static string Truncate(this string text, int maxLength, string suffix = "...")
{
    string str = text;
    if (maxLength > 0)
    {
        int length = maxLength - suffix.Length;
        if (length <= 0)
        {
            return str;
        }
        if ((text != null) && (text.Length > maxLength))
        {
            return (text.Substring(0, length).TrimEnd(new char[0]) + suffix);
        }
    }
    return str;
}

var myString = "hello world"
var myTruncatedString = myString.Truncate(4);

Returns: hello...

Answer 14

The simplest method in recent C# would be:

string Trunc(string s, int len) => s?.Length > len ? s.Substring(0, len) : s;

It returns truncated value for longer strings and original string for other cases - including null input - which is treated by ? unary operator.

Answer 15

Still no Truncate method in 2016 for C# strings. But - Using C# 6.0 Syntax:

public static class StringExtension
{
  public static string Truncate(this string s, int max) 
  { 
    return s?.Length > max ? s.Substring(0, max) : s ?? throw new ArgumentNullException(s); 
  }
}

It works like a charm:

"Truncate me".Truncate(8);
Result: "Truncate"

Answer 16

Why not:

string NormalizeLength(string value, int maxLength)
{
    //check String.IsNullOrEmpty(value) and act on it. 
    return value.PadRight(maxLength).Substring(0, maxLength);
}

i.e. in the event value.Length < maxLength pad spaces to the end or truncate the excess.

Answer 17

All the other answers do not take into account for Span's which is more performant than the Substring of the string type in .NET

If you are not already aware there is a version of System.Memory (which provides Span, ReadOnlySpan, Memory, and ReadOnlyMemory's for cases like this:

As such simple implementation for this could be as follows:

public static string Truncate(this string value, int maxLength)
{
    if (!string.IsNullOrEmpty(value) && value.Length > maxLength)
    {
        return value.AsSpan(0, maxLength).ToString(); /* Note the use of AsSpan instead of Substring. */
    }

    return value;
}

The method could theoretically be made to return Span<char> instead to avoid allocating a new string using the ToString() member of Span<T>.

The BCL itself internally uses Span's, ReadOnlySpan's, Memory's, and ReadOnlyMemory's where possible to avoid issues and to help optimize the code, especially when you compile arrays that are known at compile time and so using an property that returns that new'd up array as an ReadOnlySpan<byte> actually optimizes the code at runtime as then the JIT would not call memcpy on the data and instead uses it since it just returns a Span and as such is a window to the data that is already allocated ahead of time resulting in:

1. less allocations.
2. Less time spent allocating.
3. makes the code overall faster to use.

Answer 18

Taking @CaffGeek and simplifying it:

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

Answer 19

A similar variant with C# 6's Null propagation operator

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

Please note, we are essentially checking if value is null twice here.

Answer 20

My two cents with example length of 30 :

  var truncatedInput = string.IsNullOrEmpty(input) ? 
      string.Empty : 
      input.Substring(0, Math.Min(input.Length, 30));

Answer 21

Kndly note that truncating a string not merely means justing cutting a string at a specified length alone but have to take care not to split the word.

eg string : this is a test string.

I want to cut it at 11 . If we use any of the method given above the result will be

this is a te

This is not the thing we want

The method i am using may also not so perfect but it can handle most of the situation

public string CutString(string source, int length)
{
        if (source== null || source.Length < length)
        {
            return source;
        }
        int nextSpace = source.LastIndexOf(" ", length);
        return string.Format("{0}...", input.Substring(0, (nextSpace > 0) ? nextSpace : length).Trim());
} 

Answer 22

I know there are a ton of answers here already, but this is the one I have gone with, which handles both null strings and the situation where the length passed in is negative:

public static string Truncate(this string s, int length)
{
    return string.IsNullOrEmpty(s) || s.Length <= length ? s 
        : length <= 0 ? string.Empty 
        : s.Substring(0, length);
}

Answer 23

Just in case there's not enough answers here, here's mine :)

public static string Truncate(this string str, 
                              int totalLength, 
                              string truncationIndicator = "")
{
    if (string.IsNullOrEmpty(str) || str.Length < totalLength) 
        return str;

    return str.Substring(0, totalLength - truncationIndicator.Length) 
           + truncationIndicator;
}

to use:

"I use it like this".Truncate(5,"~")

Answer 24

The popular library Humanizer has a Truncate method. To install with NuGet:

Install-Package Humanizer

Answer 25

With C# 8 range feature and considering all kinds of inputs:

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

Answer 26

For the sake of (over)complexity I'll add my overloaded version which replaces the last 3 characters with an ellipsis in respect with the maxLength parameter.

public static string Truncate(this string value, int maxLength, bool replaceTruncatedCharWithEllipsis = false)
{
    if (replaceTruncatedCharWithEllipsis && maxLength <= 3)
        throw new ArgumentOutOfRangeException("maxLength",
            "maxLength should be greater than three when replacing with an ellipsis.");

    if (String.IsNullOrWhiteSpace(value)) 
        return String.Empty;

    if (replaceTruncatedCharWithEllipsis &&
        value.Length > maxLength)
    {
        return value.Substring(0, maxLength - 3) + "...";
    }

    return value.Substring(0, Math.Min(value.Length, maxLength)); 
}

Answer 27

There is nothing in .net for this that I am aware of - here is my version which adds "...":

public static string truncateString(string originalString, int length) {
  if (string.IsNullOrEmpty(originalString)) {
   return originalString;
  }
  if (originalString.Length > length) {
   return originalString.Substring(0, length) + "...";
  }
  else {
   return originalString;
  }
}

Answer 28

I prefer jpierson's answer, but none of the examples here that I can see are handling an invalid maxLength parameter, such as when maxLength < 0.

Choices would be either handle the error in a try/catch, clamp the maxLength parameter min to 0, or if maxLength is less than 0 return an empty string.

Not optimized code:

public string Truncate(this string value, int maximumLength)
{
    if (string.IsNullOrEmpty(value) == true) { return value; }
    if (maximumLen < 0) { return String.Empty; }
    if (value.Length > maximumLength) { return value.Substring(0, maximumLength); }
    return value;
}

Answer 29

Here is a vb.net solution, mark that the if (although ugly) statement improves performance because we do not need the substring statement when string is already smaller than maxlength... By making it an extention to string it is easy to use...

 <System.Runtime.CompilerServices.Extension()> _
    Public Function Truncate(String__1 As String, maxlength As Integer) As String
        If Not String.IsNullOrEmpty(String__1) AndAlso String__1.Length > maxlength Then
            Return String__1.Substring(0, maxlength)
        Else
            Return String__1
        End If
    End Function

Answer 30

I know there are a ton of answers already but my need was to keep the beginning and end of the string intact but shorten it to under the max length.

    public static string TruncateMiddle(string source)
    {
        if (String.IsNullOrWhiteSpace(source) || source.Length < 260) 
            return source;

        return string.Format("{0}...{1}", 
            source.Substring(0, 235),
            source.Substring(source.Length - 20));
    }

This is for creating SharePoint URLs that have a max length of 260 characters.

I didn't make length a parameter since it is a constant 260. I also didn't make the first substring length a parameter because I want it to break at a specific point. Finally, the second substring is the length of the source - 20 since I know the folder structure.

This could easily be adapted to your specific needs.