用while next訪問陣列，比foreach快上近7倍？

4八月2009 分類: 好物推薦作者: ANDY

偶然從php官網的文件，看到一篇討論while和foreach陣列訪問速度的文章，才知道有next這個關鍵字，而且搭配while來操作，速度會比foreach快上不少…真是如此嗎？花了點時間研究一下。
用while next訪問陣列，比foreach快上近7倍？

******************************************************
30870 Element Array Traversing
[test_time] [BEGINS/RESETS @ time_start = 1060977996.689]
0.2373 seg later -> while (list ($key, $val) = each ($array)) ENDS
[test_time] [BEGINS/RESETS @ time_start = 1060977996.9414]
0.1916 seg later -> while (list ($key,) = each ($array)) ENDS
[test_time] [BEGINS/RESETS @ time_start = 1060977997.1513]
0.1714 seg later -> foreach ($array AS $key=>$value) ENDS
[test_time] [BEGINS/RESETS @ time_start = 1060977997.3378]
0.0255 seg later -> while ($next = next($array)) ENDS
[test_time] [BEGINS/RESETS @ time_start = 1060977997.3771]
0.1735 seg later -> foreach ($array AS $value) ENDS
**************************************************************
foreach is fatser than a while (list - each), true.
However, a while(next) was faster than foreach.

為什麼用while next會比foreach快？那是因為foreach操作陣列時得先複製一個新的陣列變數參考，而next則是在暨有變數裡移動指標。

註1：
foreach官方文件有寫，只有在進行陣列變數參考reference操作時，才需複製一個新的陣列，該文的測試程式剛好是在用參考。

所以嚴格來講，不是while next快，而是foreach在那種狀況操作下是慢的…

註2：
另外，就該文給的測速範例來看，其實while next少算了一個（後面的討論串有提到）…

使用例：

$tests = array(
array("test1" => "123" , "test2" => "456" , "test3" => "789"),
array("test1" => "111" , "test2" => "222" , "test3" => "333"),
array("test1" => "444" , "test2" => "555" , "test3" => "666"),
array("test1" => "777" , "test2" => "888" , "test3" => "999")
);
foreach ($tests as $test) {
  echo $test['test1'].'-'.$test['test2'].'-'.$test['test3'].'';
  next($tests);
}
reset($tests);
while ($test = current($tests)) {
　　echo $test['test1'].'-'.$test['test2'].'-'.$test['test3'].'';
　　next($tests);
}

原文參考：while