之前用过
{echo discuzcode($value['message'], 0, 0, 0, 1, 1, 0, 0, 0, 0, 0);}
或者
require_once libfile('function/discuzcode');
{echo discuzcode($value['message']);}

能转大部分UBB，但是[attach]转不了。

下面是来自网络的代码，针对attach。
我用的时候做了一些修改。
<?php$thread_info = DB::fetch_first ( "select a.`tid`, a.`authorid`, a.`author`,a.`dateline`, a.`subject`, b.`message`,b.`pid`, c.`attachment` as thumb, c.`remote` from " . DB::table ( 'forum_thread' ) . " a left join " . DB::table ( 'forum_post' ) . " b on b.tid=a.tid left join " . DB::table ( 'forum_threadimage' ) . " c on c.tid=a.tid where b.pid=$pid");require_once libfile ( 'function/discuzcode' );$thread_info ['dateline'] = date ( "Y-m-d H:i:s", $thread_info ['dateline'] );$thread_info ['message'] = discuzcode ( $thread_info ['message'] );if (preg_match_all ( "/\[attach\](\d+)\[\/attach\]/i", $thread_info ['message'], $matchaids )) {$attach_ids = $matchaids [1];}$attach_list = array ();foreach ( $attach_ids as $aid ) {$find = "/\[attach\]$aid\[\/attach\]/i";$thread_info ['message'] = preg_replace ( $find, get_lw_attach_path ( $aid ), $thread_info ['message'], 1 );$thread_info ['message'] = preg_replace ( $find, '', $thread_info ['message'] );}function get_lw_attach_path($aid) {global $_G;$return = $filename = '';if ($attach = C::t ( 'forum_attachment_n' )->fetch ( 'aid:' . $aid, $aid, array (1,- 1) )) {return get_lw_attach_path_str ( $attach );}return $filename;}function get_lw_attach_path_str($attach) {global $_G;if (! $attach ['isimage']) {return '<a href="' . $_G ['siteurl'] . 'forum.php?mod=attachment&aid=' . aidencode ( $attach ['aid'] ) . '">' . $attach ['filename'] . '</a>';}if ($attach ['remote']) {$imgurl = $_G ['setting'] ['ftp'] ['attachurl'] . 'forum/' . $attach ['attachment'];return '<p><img onclick="viewimage(this);" src="' . $imgurl . '" style="max-width:834px"/></p>';} else {if (preg_match ( '/^(?!http:)/', $attach ['url'] )) {$attach ['url'] = $_G ['siteurl'] . 'data/attachment/forum/' . $attach ['url'];}$imgurl = $attach ['url'] . $attach ['attachment'] . ($_G ['gp_width'] ? '&width=' . $_G ['gp_width'] : '') . ($_G ['gp_height'] ? '&height=' . $_G ['gp_height'] : '');return '<p><a href="' . $imgurl . '" target="_blank"><img height="320" width="320" src="' . $imgurl . '" /></a></p>';}}?>
条件where b.pid=$pid，如果只调用主题帖内容，改为where a.tid=$tid and b.first=1。
$pid或$tid使用时需要先获得。

在调用帖子内容时，另外涉及到权限问题，如密码、隐藏内容、查看权限、主题售价等等。