獲取windows磁碟的可用空間函數

<?php
    /*
    *獲取某個磁碟的剩餘空間
    *$param 關聯數組，下標是哪個盤，單位，可以是B，KB，MB，GB
    *可以設置獲取多個磁碟，例如：array('C'=>'KB','D'=>'MB','E'=>'GB','F'=>'B')
    *假如出錯，返回false
    */
    function Space($arr){
        //檢查參數
        if(is_array($arr)){
            //初始化存儲值
            $memory = array();
            foreach($arr as $disk=>$size){
                $D = strtoupper($disk).':';//轉化為大寫的鍵盤路徑
                $S = strtoupper($size);//轉變為大寫的單位
                if(in_array($D,array('C:','D:','E:','F:')) && in_array($S,array('B','KB','MB','GB','TB'))){
                    switch($S){
                        case 'B':
                            $memory[$disk]= disk_free_space($D).'B';
                        break;
                        case 'KB':
                            $d = round(disk_free_space($D) / 1024);
                            $memory[$disk] = $d .'KB';
                        break;
                        case 'MB':
                            $d = round(disk_free_space($D) / pow(1024,2));
                            $memory[$disk]= $d.'MB';
                        break;
                        case 'GB':
                            $d = round(disk_free_space($D) / pow(1024,3));
                            $memory[$disk]= $d.'GB';
                        break;
                        case 'TB':
                            $d =  sprintf("%.4f", disk_free_space($D) / pow(1024,4));
                            $memory[$disk] = $d .'TB';
                        break;
                        default:
                            return 0;
                        break;
                    }
                }else{
                    return null;
                }
            }
            return $memory;
        }else{
            return null;
        }
    }
    $arr = array('c'=>'kb','d'=>'Mb','e'=>'Gb','f'=>'Tb');
    var_dump(Space($arr));