Is this a safe/strong input sanitization function?

Programmer Question

This is the sanitization function used in a book I recently learned from - "Ajax, Javascript, and PHP (Sams)". I've been using it on my own php site. Is it safe for real-world usage?

function sanitizestring($var)
{
  $var = strip_tags($var);
  $var = htmlentities($var);
  $var = stripslashes($var);
  return mysql_real_escape_string($var);
}

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