How can I truncate my strings with a "..." if they are too long?

All very good answers, but to clean it up just a little, if your strings are sentences, don't break your string in the middle of a word.

private string TruncateForDisplay(this string value, int length)
{
  if (string.IsNullOrEmpty(value)) return string.Empty;
  var returnValue = value;
  if (value.Length > length)
  {
    var tmp = value.Substring(0, length) ;
    if (tmp.LastIndexOf(' ') > 0)
       returnValue = tmp.Substring(0, tmp.LastIndexOf(' ') ) + " ...";
  }                
  return returnValue;
}

I found this question after searching for "C# truncate ellipsis". Using various answers, I created my own solution with the following features:

1. An extension method
2. Add an ellipsis
3. Make the ellipsis optional

4. Validate that the string is not null or empty before attempting to truncate it.

   public static class StringExtensions
   {
       public static string Truncate(this string value, 
           int maxLength, 
           bool addEllipsis = false)
       {
           // Check for valid string before attempting to truncate
           if (string.IsNullOrEmpty(value)) return value;
   
           // Proceed with truncating
           var result = string.Empty;
           if (value.Length > maxLength)
           {
               result = value.Substring(0, maxLength);
               if (addEllipsis) result += "...";
           }
           else
           {
               result = value;
           }
   
           return result;
       }
   }
   

I hope this helps someone else.

I has this problem recently. I was storing a "status" message in a nvarcharMAX DB field which is 4000 characters. However my status messages were building up and hitting the exception.

But it wasn't a simple case of truncation as an arbitrary truncation would orphan part of a status message, so I really needed to "truncate" at a consistent part of the string.

I solved the problem by converting the string to a string array, removing the first element and then restoring to a string. Here is the code ("CurrentStatus" is the string holding the data)...

        if (CurrentStatus.Length >= 3750)
        {
            // perform some truncation to free up some space.

            // Lets get the status messages into an array for processing...
            // We use the period as the delimiter, then skip the first item and re-insert into an array.

            string[] statusArray = CurrentStatus.Split(new string[] { "." }, StringSplitOptions.None)
                                    .Skip(1).ToArray();

            // Next we return the data to a string and replace any escaped returns with proper one.
            CurrentStatus = (string.Join(".", statusArray))
                                    .Replace("\\r\\n", Environment.NewLine);


        }

Hope it helps someone out.

Refactor with new C# features just for disclosure:

• Nullables (C# 7)
• Expression-bodied members (C# 6 and 7)
• Ranges on strings (C# 8)

// public static class StringExtensions { ...

private static string? Truncate(this string? value, int maxChars)
    =>
    string.IsNullOrEmpty(value) ? value :
    value.Length <= maxChars ? value :
    value[..maxChars] + "...";

Checked as "Community wiki", be free to improve answer.