正则表达式匹配URL——给URL地址加上<a> 链接

<?php
function replace_url ($content) {
if (empty($content)) return;

//给URL地址加上 <a> 链接
$preg = '/(?:http:\/\/)?([\w.]+[\w\/]*\.[\w.]+[\w\/]*\??[\w=\&\+\%]*)/is';
$content = preg_replace($preg, '<a href="http://\1" target="_blank">\1</a>', $content);

return $content;
}

echo replace_url('百度:http://blog.csdn.net/moqiang02');
?>