Foreach vs For循環奇怪的結果

我正在循環中運行一個簡單的測試，以查看哪個固有更快，因爲我的項目將循環超過數百萬個對象。此測試用1百萬個對象填充List，每個對象都有一個MyClass.Age屬性。我遍歷每個對象並提取Age屬性。我在Foreach循環和For循環中執行此操作。有人可以解釋的怪異的結果，或者告訴我，我犯了一個愚蠢的錯誤...感謝Foreach vs For循環奇怪的結果

static int trial = 1; 
    static void Main(string[] args) 
    { 
     while (Console.ReadKey().Key == ConsoleKey.Enter) 
     { 
      Run(); 
      trial++; 
     } 
    } 

    private static void Run() 
    { 
     Console.WriteLine(); 
     Console.WriteLine("Trial " + trial.ToString()); 

     List<MyClass> classes = new List<MyClass>(); 
     for (int x = 1; x <= 1000000; x++) 
     { 
      classes.Add(new MyClass(x)); 
     } 

     DateTime startTime = new DateTime(); 
     DateTime endTime = new DateTime(); 

     DateTime startTime2 = new DateTime(); 
     DateTime endTime2 = new DateTime(); 

     startTime = DateTime.Now; 
     foreach (MyClass c in classes) 
     { 
      int age = c.Age; 
     } 
     endTime = DateTime.Now; 
     TimeSpan span = endTime - startTime; 
     Console.WriteLine("ForEach Time: " + span.TotalMilliseconds.ToString("#,##0.00000").PadLeft(10) + "ms"); 


     startTime2 = DateTime.Now; 
     for (int x = 0; x < classes.Count; x++) 
     { 
      int age = classes[x].Age; 
     } 
     endTime2 = DateTime.Now; 
     TimeSpan span2 = endTime2 - startTime2; 
     Console.WriteLine("ForLoop Time: " + span2.TotalMilliseconds.ToString("#,##0.00000").PadLeft(10) + "ms"); 
    } 

    class MyClass 
    { 
     public int Age; 

     public MyClass(int a) 
     { 
      Age = a; 
     } 
    }

結果：

Trial 1 
ForEach Time: 15.60000ms 
ForLoop Time:  0.00000ms 

Trial 2 
ForEach Time:  0.00000ms 
ForLoop Time: 15.60000ms 

Trial 3 
ForEach Time: 15.60000ms 
ForLoop Time:  0.00000ms 

Trial 4 
ForEach Time: 15.60000ms 
ForLoop Time:  0.00000ms 

Trial 5 
ForEach Time: 15.60010ms 
ForLoop Time:  0.00000ms 

Trial 6 
ForEach Time:  0.00000ms 
ForLoop Time:  0.00000ms 

Trial 7 
ForEach Time: 15.60000ms 
ForLoop Time:  0.00000ms 

Trial 8 
ForEach Time: 15.60010ms 
ForLoop Time:  0.00000ms 

Trial 9 
ForEach Time:  0.00000ms 
ForLoop Time: 15.60010ms 

Trial 10 
ForEach Time:  0.00000ms 
ForLoop Time:  0.00000ms

來源

2016-11-08 user2777664

您應該使用，而不是使用DateTime.Now正確System.Diagnostic.StopWatch類時間經過比較

來源

2016-11-08 01:58:48 Rahul

修正了它。你介意爲什麼Datetime.Now這樣行事嗎？ – user2777664

@ user2777664，是的。檢查這篇文章http://stackoverflow.com/questions/2923283/stopwatch-vs-using-system-datetime-now-for-timing-events（或）MSDN文檔。簡而言之，'stopwatch'比'DateTime.Now'提供更高的精度。 – Rahul

謝謝！我很感激。 – user2777664

Foreach vs For循環奇怪的結果

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