Why does System.Uri interpret two slashes in a row as folder?

Question

I've gotten into the habit of always putting a trailing slash at the end of my folder paths and this appears to be the norm (e.g. Visual Studio macros such as $(ProjectDir) always have a trailing slash). In addition, when I'm appending a relative path to the end of an existing folder path I always put a leading slash just in case the folder path that is passed to me doesn't have a trailing slash (e.g. Windows batch: set FULL_FILE_PATH=%FOLDER_PATH%\path\to\some\file).

That being said, I tend to end up with paths that look like this C:\path\to\folder\\path\to\some\file.txt (note the two backslashes in a row). In addition, since I'm using dev\src dev\include and dev\script folder structure (where .vcxproj files and similar go in the script folder), most of my paths append a relative path with up-levels to at the end of some macro like $(ProjectDir) (e.g. Include dir = $(ProjectDir)\..\include\).

In the following code somePath02Uri and somePath03Uri return (what I believe to be) incorrect results:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DotNet45SystemUriTest
{
   class Program
   {
      static void Main(string[] args)
      {
         Console.WriteLine("We will now test the System.Uri constructor:\n");

         // Output from Console.WriteLine is in the comment on the same line

         String somePath01 = "C:\\some\\common\\..\\include\\";
         Console.WriteLine("somePath01 = " + somePath01); // somePath01 = C:\some\common\..\include\
         Uri somePath01Uri = new Uri(somePath01);
         Console.WriteLine("somePath01Uri = " + somePath01Uri.ToString()); // somePath01Uri = file:///C:/some/include/

         Console.WriteLine();

         String somePath02 = "C:\\some\\common\\\\..\\include\\";
         Console.WriteLine("somePath02 = " + somePath02); // somePath02 = C:\some\common\\..\include\
         Uri somePath02Uri = new Uri(somePath02);
         Console.WriteLine("somePath02Uri = " + somePath02Uri.ToString()); // somePath02Uri = file:///C:/some/common/include/

         Console.WriteLine();

         String somePath03 = "C:\\some\\common\\\\\\..\\include\\";
         Console.WriteLine("somePath03 = " + somePath03); // somePath03 = C:\some\common\\\..\include\
         Uri somePath03Uri = new Uri(somePath03);
         Console.WriteLine("somePath03Uri = " + somePath03Uri.ToString()); // somePath03Uri = file:///C:/some/common//include/

         Console.WriteLine();
      }
   }
}

Why does System.Uri interpret two slashes in a row as folder?

Almost forgot: If you do encounter this a quick and dirty solution is to remove the two backslashes in a row from the string before creating the Uri object. I did this by adding .Replace("\\\\", "\\"):

         String somePath02 = "C:\\some\\common\\\\..\\include\\";
         Console.WriteLine("somePath02 = " + somePath02); // somePath02 = C:\some\common\\..\include\
         Uri somePath02Uri = new Uri(somePath02.Replace("\\\\", "\\"));
         Console.WriteLine("somePath02Uri = " + somePath02Uri.ToString()); // somePath02Uri = file:///C:/some/include/

Answer 1

The two slashes ar used for non escaping.

For example try this:

string path = "c:\test\html";

When you compile this piece of code you will get an error "Unrecognized escape sequence".

But if you add an extra slash, you tell the complier that there is no escaping intended and the string should be parsed as it is.

string path = "c:\\test\\html";

Another intresting method for non escaping is:

string path = @"c:\test\html";