PHP截取字符串 兼容utf-8 gb2312

<?php
        function subString($string,$length,$append = false) {
            if(strlen($string) <= $length ) {
                return $string;
            }else{
                $i = 0;
                while ($i < $length){
                    $stringTMP = substr($string,$i,1);
                    if ( ord($stringTMP) >=224 ){
                        $stringTMP = substr($string,$i,3);
                        $i = $i + 3;
                    }elseif( ord($stringTMP) >=192 ){
                        $stringTMP = substr($string,$i,2);
                        $i = $i + 2;
                    }else{
                        $i = $i + 1;
                    }
                    $stringLast[] = $stringTMP;
                }
                $stringLast = implode("",$stringLast);
                if($append){
                    $stringLast .= "...";
                }
                return $stringLast;
            }
        }

        $string = "输不起de青春 —— phper";
        $length = "26";
        $append = true;
        echo subString($string,$length,$append);
?>