title: C# regular expressions - matching whole words?
body: <p>I am writing a program that needs to search a LARGE text document for a large collection of words.  The words are all file names, with underscores in them (eg, this_file_name).  I know how to open and iterate through a text document, but I'm curious whether I should use Regex to search for these names, and if so, what kind of reg. ex. sequence should I use?   I've tried </p>
  
  <pre>
  Regex r = new Regex("?this\_file\_name");
  </pre>
  
  <p>but I get an invalid argument error every time.</p>