C#: Implementation of, or alternative to, StrCmpLogicalW in shlwapi.dll

Question

For natural sorting in my application I currently P/Invoke a function called StrCmpLogicalW in shlwapi.dll. I was thinking about trying to run my application under Mono, but then of course I can't have this P/Invoke stuff (as far as I know anyways).

Is it possible to see the implementation of that method somewhere, or is there a good, clean and efficient C# snippet which does the same thing?

My code currently looks like this:

[SuppressUnmanagedCodeSecurity]
internal static class SafeNativeMethods
{
    [DllImport("shlwapi.dll", CharSet = CharSet.Unicode)]
    public static extern int StrCmpLogicalW(string psz1, string psz2);
}

public class NaturalStringComparer : IComparer<string>
{
    private readonly int modifier = 1;

    public NaturalStringComparer() : this(false) {}
    public NaturalStringComparer(bool descending)
    {
        if (descending) modifier = -1;
    }

    public int Compare(string a, string b)
    {
        return SafeNativeMethods.StrCmpLogicalW(a ?? "", b ?? "") * modifier;
    }
}

So, what I'm looking for is an alternative to the above class which doesn't use an extern function.

Answer 1

I just implemented natural string comparison in C#, perhaps someone might find it useful:

public class NaturalComparer : IComparer<string>
{
   public int Compare(string x, string y)
   {
      if (x == null && y == null) return 0;
      if (x == null) return -1;
      if (y == null) return 1;

      int lx = x.Length, ly = y.Length;

      for (int mx = 0, my = 0; mx < lx && my < ly; mx++, my++)
      {
         if (char.IsDigit(x[mx]) && char.IsDigit(y[my]))
         {
            long vx = 0, vy = 0;

            for (; mx < lx && char.IsDigit(x[mx]); mx++)
               vx = vx * 10 + x[mx] - '0';

            for (; my < ly && char.IsDigit(y[my]); my++)
               vy = vy * 10 + y[my] - '0';

            if (vx != vy)
               return vx > vy ? 1 : -1;
         }

         if (mx < lx && my < ly && x[mx] != y[my])
            return x[mx] > y[my] ? 1 : -1;
      }

      return lx - ly;
   }
}

Answer 2

http://www.interact-sw.co.uk/iangblog/2007/12/13/natural-sorting seems to be what you're looking for.

(and no, there is no managed equivalent to StrCmpLogicalW built into .NET)

Answer 3

I used regular expression to remove special characters. then casting to int. then i compared integers.

input :

List input = new List{ "6.04","6.01","6.03","6#04" };

Expected Output:

6.01
6.03
6.04
6#04

 var output = input.OrderBy(s => s, new NaturalStringComparer());
            foreach (var sort in output)
            {
                Console.WriteLine(sort);
            }


public struct NaturalStringComparer : IComparer
    {
        public int Compare(string x, string y)
        {
            if (x == null && y == null) return 0;
            if (x == null) return -1;
            if (y == null) return 1;

            int lx = x.Length, ly = y.Length;

            int a = int.Parse(System.Text.RegularExpressions.Regex.Replace(x, @"\D+", ""));
            int b = int.Parse(System.Text.RegularExpressions.Regex.Replace(y, @"\D+", ""));

            return a.CompareTo(b);
        }
    }

Answer 4

If you're running on Windows XP or newer, you can PInvoke to the shell function StrCmpLogicalW:

public static int StrCmpLogical(String s1, String s2)
{
    if (String.IsNullOrEmpty(s1) && !String.IsNullOrEmpty(s2))
        return 1; //empty s1 comes after s2
    else if (String.IsNullOrEmpty(s2) && !String.IsNullOrEmpty(s1))
        return -1; //non-empty string comes before empty

    return SafeNativeMethods.StrCmpLogicalW(s1, s2);
}

And then the internal unsafe class:

/// <summary>
/// This class suppresses stack walks for unmanaged code permission. 
/// (System.Security.SuppressUnmanagedCodeSecurityAttribute is applied to this class.) 
/// This class is for methods that are safe for anyone to call. 
/// Callers of these methods are not required to perform a full security review to make sure that the 
/// usage is secure because the methods are harmless for any caller.
/// </summary>
[SuppressUnmanagedCodeSecurity]
internal static class SafeNativeMethods
{
    [DllImport("shlwapi.dll", CharSet = CharSet.Unicode)]
    internal static extern Int32 StrCmpLogicalW(string psz1, string psz2);
}