最后的帖子文本限制phpbb中的字符

我找到了这个代码，用于在phpbb论坛中显示最后的帖子。我想在post_text中设置字符限制。

<?php
    // Now let's output the content
    // A ted vypsat obsah
    while ($row = $db->sql_fetchrow($result))
    {
$url = generate_board_url() . "/viewtopic.{$phpEx}?f={$row['forum_id']}&amp;t={$row['topic_id']}&amp;p={$row['post_id']}#p{$row['post_id']}"; //added fedforum to url
$urlmini = generate_board_url() . "/memberlist.{$phpEx}?mode=viewprofile&u={$row['poster_id']}"; //added fedforum to url
//old line $url = generate_board_url() . "viewtopic.{$phpEx}?f={$row['forum_id']}&amp;t={$row['topic_id']}&amp;p={$row['post_id']}#p{$row['post_id']}";      
 echo '<small><a target="_blank" href="' . $url . '">' . $row['post_subject']. '</a><br>'. $row['post_text'] .'<br>od: <a target="_blank" href="' . $urlmini . '">' . ucwords($row['username']).'</a>' . ' v '.'<font style="color:#aaa;">' . date("H:i",$row['post_time']).'</font>', '<br><br></small>';
    }
    ?>

有谁知道如何为$row['post_text']设置字符限制？