mb_substr 文章截取

$frontcontent=$newssection_result->fields['post_content'];
$frontcontent = str_replace(']]>', ']]>', $frontcontent);
$pattern='/]+./';
$patternhref='//i';
$frontcontent = preg_replace($pattern,'', $frontcontent);
$frontcontent = preg_replace($patternhref,'', $frontcontent);
$frontcontent = strip_tags($frontcontent);
//$contentrest = substr($frontcontent, 0, 101);
$contentrest = mb_substr($frontcontent,0,80,'utf-8');