php字符串太长怎么办

if (! function_exists('mbSubStr')){
    function mbSubStr($str, $length = 0, $append = true)
    {
        $str = trim($str);
        $strlength = strlen($str);
        if ($length == 0 || $length >= $strlength) {
            return $str;  //截取长度等于0或大于等于本字符串的长度，返回字符串本身
        }elseif ($length < 0){  //如果截取长度为负数
            $length = $strlength + $length;//那么截取长度就等于字符串长度减去截取长度
            if ($length < 0) {
                $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
            }
        }
        if (function_exists('mb_substr')){
            $newstr = mb_substr($str, 0, $length, 'utf-8');
        }elseif (function_exists('iconv_substr')){
            $newstr = iconv_substr($str, 0, $length, 'utf-8');
        }else{
            //$newstr = trim_right(substr($str, 0, $length));
            $newstr = substr($str, 0, $length);
        }
        if ($append && $str != $newstr){
            $newstr .= '...';
        }
        return $newstr;
    }
}