title: match-string in elisp not returning string matched by string-match
body: <p>I have a problem where I fail to get a match-string after a string-match. I think the string-match works, at least it returns non nil, but I get an error when I try to get the match-string. How should I do it?</p>
  
  <p>The failing function:</p>
  
  <pre><code>(defun small-test ()
    (string-match "\\([0-9]+\\)-v\\([0-9]+\\).txt" "2011-v9.txt")
    (message (match-string 1))
    )
  </code></pre>