PHP - stripping the extension from a file name string

I want to strip the extension from a filename, and get the file name - e.g. file.xml -> file, image.jpeg -> image, test.march.txt -> test.march, etc.

So I wrote this function

function strip_extension($filename) {
   $dotpos = strrpos($filename, ".");
   if ($dotpos === false) {
      $result = $filename;
   }
   else {
      $result = substr($filename,0,$dotpos);
   }
   return $result;
}

Which returns an empty string.

I can't see what I'm doing wrong?