using System;

public class Program

{

    public static void Main()

    {

        string testString = "abcde";

        var testSuite = new int?[] {

            -1,null,    -1, -1,     -1, 0,    -1, 1,    -1, 3,   -1,9,

            -0,null,     0, -2,     -0, 2,     0, 5,     0, 9,

            2,null,     2, -3,      2,-2,     2,-1,     2, 0,    2,2,      2,6,

            4,null,     4, -9,      4,-4,     4, 0,     4, 1,    4,4,      4,9,

            5,null,     5, -9,      5,-5,     5,-4,     5,-0,    5,1,

            6,null,     6, -9,      6,-6,     6,-5,     6,-2,    6,0,      6,2};

        Console.WriteLine("\r\nTesting Base and Extension 'Substring()' Methods for \"" + testString + "\".Substring(startIndx, length, handleIndexException: true): ");

        Console.WriteLine("Start  Length  Extn Result  Base Method Result\r\n" + new string('=', 80));

        for (int i = 0; i < testSuite.Length; i += 2)

        {

            int x = (int)testSuite[i];

            int? y = testSuite[i + 1];

            string rsltExt = (y.HasValue ? testString.Substring(x, (int)y, true) : testString.Substring(x, true));

            string rsltBase = "";

        try

        {

            rsltBase = (y.HasValue ? testString.Substring(x, (int)y):testString.Substring(x));

        }

        catch (Exception ex)

        {

            rsltBase = "***Exception: " + ex.Message.Split('\r')[0];

        }

            Console.WriteLine("{0,3}    {1,4}    {2,-12} {3}", x, y, rsltExt.ShowNull(), rsltBase.ShowNull());

        }

    }

}

public static class Extensions

{

    /// <summary>

    /// String Extension returns "<<null>>" some other value to indicate that the string value was null

    /// </summary>

    /// <param name="val"></param>

    /// <param name="nullval">Optional: pass your choice of value to display if string is null</param>

    /// <returns></returns>

    public static String ShowNull(this String val, string nullval = "<<null>>"){

        return string.IsNullOrEmpty(val) ? nullval : val;

    }

​

    /// <summary>

    /// String Extension for Substring with startIndex, that intelligently handles out-of-bounds scenerios instead of returning exception

    /// see http://jagdale.blogspot.com/2010/05/substring-extension-method-that-does.html

    /// </summary>

    /// <param name="val"></param>

    /// <param name="startIndex"></param>

    /// <param name="handleIndexException"></param>

    /// <returns>if set to "true" handles intelligently handles the exception, otherwise works like regular Substring</returns>

    public static String Substring(this String val, int startIndex, bool handleIndexException)

    {

        if (!handleIndexException){ //handleIndexException is false so call the base method

            return val.Substring(startIndex);

        }

        if (string.IsNullOrEmpty(val)){

            return val;

        }

        return val.Substring(startIndex < 0 ? 0 : startIndex > (val.Length - 1) ? val.Length : startIndex);

    }

    /// <summary>

    /// String Extension for Substring with startIndex and Length, that intelligently handles out-of-bounds scenerios instead of returning exception

    /// see http://jagdale.blogspot.com/2010/05/substring-extension-method-that-does.html

    /// </summary>

    /// <param name="val"></param>

    /// <param name="startIndex"></param>

    /// <param name="length"></param>

    /// <param name="handleIndexException"></param>

    /// <returns>if set to "true" handles intelligently handles the exception, otherwise works like regular Substring</returns>

    public static String Substring(this String val, int startIndex, int length, bool handleIndexException)

    {

        if (!handleIndexException){ //handleIndexException is false so call the base method

            return val.Substring(startIndex, length);

        }

        if (string.IsNullOrEmpty(val))

        {

            return val;

        }

        int newfrom, newlth, instrlength = val.Length;

        if (length < 0) //length is negative

        {

            newfrom = startIndex + length;

            newlth = -1 * length;

        }

        else //length is positive

        {

            newfrom = startIndex;

            newlth = length;

        }

        if (newfrom + newlth < 0 || newfrom > instrlength - 1)

        {

            return string.Empty;

        }

        if (newfrom < 0)

        {

            newlth = newfrom + newlth;

            newfrom = 0;

        }

        return val.Substring(newfrom, Math.Min(newlth, instrlength - newfrom));

    }

}