Best way to break a string on the last dot on C#

What would be the best way and more idiomatic to break a string into two at the place of the last dot? Basically separating the extension from the rest of a path in a file path or URL. So far what I'm doing is Split(".") and then String.Join(".") of everything but the last part. Sounds like using a bazooka to kill flies.

From stackoverflow

• You could use Path.GetFilenameWithoutExtension()

  or if that won't work for you:

  int idx = filename.LastIndexOf('.');
  
  if (idx >= 0)
     filename = filename.Substring(0,idx);
  

  J. Pablo Fernández : Will that work on pieces of URL (using / instead of \)? And will it also return the "folders"? Path.GetFilename() returns only the name of the file, without directories, AFAIK.

  OregonGhost : If the OP had asked about file paths only, this would be a +1. But the System.IO.Path docs don't mention support for URLs.

  Philippe Leybaert : Correct, but it may have worked for you if the filename didn't include a path.

  Pondidum : +1 for IO.Path.*

  jmservera : Does not mention it, but it works.

  OregonGhost : It might work, but unfortunately that means relying on an undocumented feature. If that's fine for you, System.IO.Path is the solution to the problem.

• The string method LastIndexOf maybe of some use to you here.

  But the Path or FileInfo operators will be better suited for filename based operations.

• I think what you're really looking for is Path.GetFileNameWithoutExtension Method (System.IO) but just for the heck of it:

  string input = "foo.bar.foobar";
  int lastDotPosition = input.LastIndexOf('.');
  
  if (lastDotPosition == -1)
  {
      Console.WriteLine("No dot found");
  }
  else if (lastDotPosition == input.Length - 1)
  {
      Console.WriteLine("Last dot found at the very end");
  
  }
  else
  {
      string firstPart = input.Substring(0, lastDotPosition);
      string lastPart = input.Substring(lastDotPosition + 1);
  
      Console.WriteLine(firstPart);
      Console.WriteLine(lastPart);
  }
  

• To get the path without the extension, use

  System.IO.Path.GetFileNameWithoutExtension(fileName)
  

  and to get the extenstion (including the dot), use

  Path.GetExtension(fileName)
  

  EDIT:

  Unfortunately GetFileNameWithoutExtension strips off the leading path, so instead you could use:

  if (path == null)
  {
      return null;
  }
  int length = path.LastIndexOf('.');
  if (length == -1)
  {
      return path;
  }
  return path.Substring(0, length);
  

  jmservera : It also works with urls

• Path.GetExtension() should help you.

• If you want performance, something like:

      string s = "a.b.c.d";
      int i = s.LastIndexOf('.');
      string lhs = i < 0 ? s : s.Substring(0,i),
          rhs = i < 0 ? "" : s.Substring(i+1);
  

• What about using the LastIndexOf method which returns the last found position of a character. Then you can use Substring to extract what you want.

• String.LastIndexOf will return you the position of the dot if it ever exists in the string. You can then String.Substring methods to split the string.

• You can use string's method

  LastIndexOf and substring to acomplish the task.