文本去掉BOM头

  /**
     * 检查P文件中是否含有bom头
     * @param $filename string 文件路径
     * @param $isRewrite boolean  是否重写为不含bom头的文件
     * @return boolean
     */
        function checkBOM($filename,$isRewrite =false){
            $contents = file_get_contents($filename);
            $charset[1] = substr($contents, 0, 1);
            $charset[2] = substr($contents, 1, 1);
            $charset[3] = substr($contents, 2, 1);
            if(ord($charset[1]) == 239 && ord($charset[2]) == 187 && ord($charset[3]) == 191){
                if($isRewrite){
                    $rest = substr($contents, 3);
                    rewrite ($filename, $rest);
                }
                return true;
            }
            else return false;
        }

        function rewrite($filename, $data){
            $filenum = fopen($filename, "w");
            flock($filenum, LOCK_EX);
            fwrite($filenum, $data);
            fclose($filenum);
        }