php中将网址转换为超链接的函数

function showtext($text){ 
$search = array('|(http://[^ ]+)|', '|(https://[^ ]+)|', '|(www.[^ ]+)|'); 
$replace = array('<a href="$1" target="_blank">$1</a>', '<a href="$1" target="_blank">$1</a>', '<a href="http://$1" target="_blank">$1</a>'); 
$text = preg_replace($search, $replace, $text); 
return $text; 
}