以@CaffGeek为例进行简化:

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

在。net中我没有意识到这一点-这里是我的版本，它增加了“…”:

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;
  }
}

另一个解决方案:

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

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;
}

所有其他答案都没有考虑到Span的性能，它比。net中字符串类型的Substring的性能更好

如果你还不知道有一个版本的系统。内存(为以下情况提供了Span, ReadOnlySpan, Memory和ReadOnlyMemory:

这样的简单实现可以如下所示:

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;
}

该方法理论上可以返回Span<char>，以避免使用Span<T>的ToString()成员分配新字符串。

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:

更少的分配。 更少的分配时间。 使代码总体上更快地使用。

我想我应该加入我的实现，因为我相信它涵盖了其他人所涉及的所有情况，并且以一种简洁的方式做到了这一点，仍然是可读的。

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

    return value;
}

该解决方案主要构建在Ray的解决方案之上，并通过使用This关键字将该方法作为扩展方法使用，就像LBushkin在他的解决方案中所做的那样。