NaturalStringComparer.cs

// Adapted from Greg Beech's blog post:
// http://gregbee.ch/blog/natural-sort-order-of-strings-and-file
// Distributed under the Creative Commons Zero (CC0) license.

using System.Collections.Generic;
using System.Runtime.InteropServices;
using System.Security;

/// <summary>
/// A string comparer that uses the StrCmpLogicalW function for natural string comparisons.
/// </summary>
class NaturalStringComparer : IComparer<string>
{
    /// <summary>
    /// Contains native methods used by this class.
    /// </summary>
    [SuppressUnmanagedCodeSecurity]
    private static class SafeNativeMethods
    {
        [DllImport("shlwapi.dll", CharSet = CharSet.Unicode, ExactSpelling = true)]
        public static extern int StrCmpLogicalW(string psz1, string psz2);
    }

    /// <summary>
    /// Gets a default instance of the NaturalStringComparer class.
    /// </summary>
    public static NaturalStringComparer Default { get; private set; }

    /// <summary>
    /// Initializes static members of the NaturalStringComparer class.
    /// </summary>
    static NaturalStringComparer()
    {
        Default = new NaturalStringComparer();
    }

    /// <summary>
    /// Compares two strings and returns a value indicating whether one is less than, equal to,
    /// or greater than the other.
    /// </summary>
    /// <param name="x">The first string to compare.</param>
    /// <param name="y">The second string to compare.</param>
    /// <returns>
    /// An int that is: zero if x equals y; less than zero if x is less than y; greater than
    /// zero if x is greater than y.
    /// </returns>
    public int Compare(string x, string y)
    {
        return SafeNativeMethods.StrCmpLogicalW(x, y);
    }
}