Getting path relative to the current working directory

Question

I'm writing a console utility to do some processing on files specified on the commandline, but I've run into a problem I can't solve through Google/SO. If a full path, including drive letter, is specified, how do I reformat that path to be relative to the current working directory?

There must be something similar to the VirtualPathUtility.MakeRelative function, but if there is, it eludes me.

Answer 1

You can use Environment.CurrentDirectory to get the current directory, and FileSystemInfo.FullPath to get the full path to any location. So, fully qualify both the current directory and the file in question, and then check whether the full file name starts with the directory name - if it does, just take the appropriate substring based on the directory name's length.

Here's some sample code:

using System;
using System.IO;

class Program
{
    public static void Main(string[] args)
    {
        string currentDir = Environment.CurrentDirectory;
        DirectoryInfo directory = new DirectoryInfo(currentDir);
        FileInfo file = new FileInfo(args[0]);

        string fullDirectory = directory.FullName;
        string fullFile = file.FullName;

        if (!fullFile.StartsWith(fullDirectory))
        {
            Console.WriteLine("Unable to make relative path");
        }
        else
        {
            // The +1 is to avoid the directory separator
            Console.WriteLine("Relative path: {0}",
                              fullFile.Substring(fullDirectory.Length+1));
        }
    }
}

I'm not saying it's the most robust thing in the world (symlinks could probably confuse it) but it's probably okay if this is just a tool you'll be using occasionally.

Answer 2

If you don't mind the slashes being switched, you could [ab]use Uri:

Uri uri1 = new Uri(@"c:\foo\bar\blop\blap");
Uri uri2 = new Uri(@"c:\foo\bar\");
string relativePath = uri2.MakeRelativeUri(uri1).ToString();