这段随机调用的代码，怎么限制调出的标题字数为36个字符？

请问这段随机调用的代码，怎么限制调出的标题字数为36个字符？谢谢！

  <?php
$sql="SELECT * FROM {$dbtbpre}ecms_news AS t1 JOIN (SELECT ROUND(RAND() * ((SELECT MAX(id) FROM {$dbtbpre}ecms_news )-(SELECT MIN(id) FROM {$dbtbpre}ecms_news))+(SELECT MIN(id)
FROM {$dbtbpre}ecms_news )) AS id2) AS t2 WHERE t1.id >= t2.id2 ORDER BY t1.id LIMIT 1";
$str="";
$rid=array();
$i=0;
while($i<10){
$nr= $empire->fetch1($sql);
$titleurl=sys_ReturnBqTitleLink($nr);
if(in_array($nr['id'], $rid)){
} else {
$str=$str."<li><a href='".$titleurl."' title='".$nr['title']."'>".$nr['title']."</a></li> ";
$rid[]=$nr['id'];
$i=$i+1;
}
}
echo $str;
?>