php中怎么对输出的文章限制字数，剩余的用“.”表示

echo mb_strlen($news['n_content'], 'utf-8') > 9 ? mb_substr($news['n_content'], 0, 9, 'utf-8').'....' : $news['n_content'];

<br />/**<br /> * 字符串截取<br /> *<br /> */<br />function sub_str($str, $length = 0, $append = true)<br />{<br />    $str = trim($str);<br />    $strlength = strlen($str);<br /><br />    if ($length == 0 <br><font color='#FF8000'>------解决思路----------------------</font><br> $length >= $strlength)<br />    {<br />        return $str;  //截取长度等于0或大于等于本字符串的长度，返回字符串本身<br />    }<br />    elseif ($length < 0)  //如果截取长度为负数<br />    {<br />        $length = $strlength + $length;//那么截取长度就等于字符串长度减去截取长度<br />        if ($length < 0)<br />        {<br />            $length = $strlength;//如果截取长度的绝对值大于字符串本身长度，则截取长度取字符串本身的长度<br />        }<br />    }<br /><br />    if (function_exists('mb_substr'))<br />    {<br />        $newstr = mb_substr($str, 0, $length, EC_CHARSET);<br />    }<br />    elseif (function_exists('iconv_substr'))<br />    {<br />        $newstr = iconv_substr($str, 0, $length, EC_CHARSET);<br />    }<br />    else<br />    {<br />        //$newstr = trim_right(substr($str, 0, $length));<br />        $newstr = substr($str, 0, $length);<br />    }<br /><br />    if ($append && $str != $newstr)<br />    {<br />        $newstr .= '...';<br />    }<br /><br />    return $newstr;<br />}<br />