C# - String Truncate - Dot Net Perls

Truncate. This C# method restricts the maximum length of strings. We truncate a string so that it has a substring of the first specified number of letters.

Truncate is useful for text in databases or in user interfaces where space is limited. It can be helpful when justifying text to the right as well.

String Substring

An example. The string type does not provide a Truncate method. We must use a conditional expression and either Substring or Remove.

Tip Looking in IL Disassembler, Remove calls into Substring. So these custom methods directly call Substring.

String Remove

Detail If the source is longer than the max length, we call Substring to get the first N characters. This copies the string.

Detail Use a nested Math.Min expression in a Substring call. In this method, the Substring method is always entered.

Math.Max, Math.Min

Info By always entering the Substring method, we may create string copies that are not needed.

using System;

class Program
{
    static void Main()
    {
        string result = StringTool.Truncate("Carrot", 3);
        string result2 = StringTool.Truncate2("Carrot", 3);
        Console.WriteLine(result);
        Console.WriteLine(result2);

        result = StringTool.Truncate("Computer", 20);
        result2 = StringTool.Truncate2("Computer", 20);
        Console.WriteLine(result);
        Console.WriteLine(result2);
    }
}

/// <summary>
/// Custom string utility methods.
/// </summary>
public static class StringTool
{
    /// <summary>
    /// Get a substring of the first N characters.
    /// </summary>
    public static string Truncate(string source, int length)
    {
        if (source.Length > length)
        {
            source = source.Substring(0, length);
        }
        return source;
    }

    /// <summary>
    /// Get a substring of the first N characters. [Slow]
    /// </summary>
    public static string Truncate2(string source, int length)
    {
        return source.Substring(0, Math.Min(length, source.Length));
    }
}Car
Car
Computer
Computer

Performance. I wanted to know if avoiding Substring() when it is not needed would have an impact on performance. And I found using the if-statement before calling Substring is faster.

Version 1 This code calls Truncate, which uses an if-statement to avoid calling Substring if the truncation does not need to occur.

Benchmark

Version 2 This code always uses substring, but uses Math.Min to ensure we do not take a substring that is too long.

Result Truncate, which avoids calling Substring(), is faster. It avoids a string method call in the benchmark.

using System;
using System.Diagnostics;

class Program
{
    public static class StringTool
    {
        public static string Truncate(string source, int length)
        {
            if (source.Length > length)
            {
                source = source.Substring(0, length);
            }
            return source;
        }

        public static string Truncate2(string source, int length)
        {
            return source.Substring(0, Math.Min(length, source.Length));
        }
    }

    const int _max = 100000000;
    static void Main()
    {
        var s1 = Stopwatch.StartNew();
        // Version 1: use Truncate.
        for (int i = 0; i < _max; i++)
        {
            string a = StringTool.Truncate("Carrot", 3);
            string b = StringTool.Truncate("Carrot", 10);
        }
        s1.Stop();
        // Version 2: use Truncate2.
        var s2 = Stopwatch.StartNew();
        for (int i = 0; i < _max; i++)
        {
            string a = StringTool.Truncate2("Carrot", 3);
            string b = StringTool.Truncate2("Carrot", 10);
        }
        s2.Stop();
        Console.WriteLine(((double)(s1.Elapsed.TotalMilliseconds * 1000000) / _max).ToString("0.00 ns"));
        Console.WriteLine(((double)(s2.Elapsed.TotalMilliseconds * 1000000) / _max).ToString("0.00 ns"));
    }
}14.18 ns    Truncate
15.28 ns    Truncate2

A summary. Here we saw 2 implementations of string Truncate. We validated that they have correct results. Avoiding the Substring call when it is not necessary is faster.