Showing only a certain amount of characters from a value

I'm trying to display the description of someones article. I want to take the first 100 characters of their article and use it as their description, so my question is, is there a function that allows me to limit 100 characters of a value.

Thanks

$string = substr($string, 0, 100);

substr() (http://uk2.php.net/manual/en/function.substr.php)