Given full path, check if path is subdirectory of some other path, or otherwise

Question

I have 2 strings - dir1 and dir2, and I need to check if one is sub-directory for other. I tried to go with Contains method:

dir1.contains(dir2);
         


        

Answer 1

Based on @BrokenGlass's answer but tweaked:

using System.IO;

internal static class DirectoryInfoExt
{
    internal static bool IsSubDirectoryOfOrSame(this DirectoryInfo directoryInfo, DirectoryInfo potentialParent)
    {
        if (DirectoryInfoComparer.Default.Equals(directoryInfo, potentialParent))
        {
            return true;
        }

        return IsStrictSubDirectoryOf(directoryInfo, potentialParent);
    }

    internal static bool IsStrictSubDirectoryOf(this DirectoryInfo directoryInfo, DirectoryInfo potentialParent)
    {
        while (directoryInfo.Parent != null)
        {
            if (DirectoryInfoComparer.Default.Equals(directoryInfo.Parent, potentialParent))
            {
                return true;
            }

            directoryInfo = directoryInfo.Parent;
        }

        return false;
    }
}

using System;
using System.Collections.Generic;
using System.IO;

public class DirectoryInfoComparer : IEqualityComparer
{
    private static readonly char[] TrimEnd = { '\\' };
    public static readonly DirectoryInfoComparer Default = new DirectoryInfoComparer();
    private static readonly StringComparer OrdinalIgnoreCaseComparer = StringComparer.OrdinalIgnoreCase;

    private DirectoryInfoComparer()
    {
    }

    public bool Equals(DirectoryInfo x, DirectoryInfo y)
    {
        if (ReferenceEquals(x, y))
        {
            return true;
        }

        if (x == null || y == null)
        {
            return false;
        }

        return OrdinalIgnoreCaseComparer.Equals(x.FullName.TrimEnd(TrimEnd), y.FullName.TrimEnd(TrimEnd));
    }

    public int GetHashCode(DirectoryInfo obj)
    {
        if (obj == null)
        {
            throw new ArgumentNullException(nameof(obj));
        }
        return OrdinalIgnoreCaseComparer.GetHashCode(obj.FullName.TrimEnd(TrimEnd));
    }
}

Not ideal if performance is essential.