これもフィルターをひっかける
add_filter('the_content', 'url2href');
function url2href($content) {
if ( is_singular() ) {
//外部サイト
$content = preg_replace("/(https?:\/\/)(?!{$_SERVER["HTTP_HOST"]})([-_.!~*'()a-zA-Z0-9;\/?:\@&=+\$,%#]+)/", "<a href=\"\\1\\2\" target=\"_blank\" rel=\"nofollow\">\\1\\2</a>", $content);
//自サイト
$content = preg_replace("/(https?:\/\/{$_SERVER["HTTP_HOST"]})([-_.!~*'()a-zA-Z0-9;\/?:\@&=+\$,%#]+)/", "<a href=\"\\2\">\\1\\2</a>", $content);
}
return $content;
}