Question

我在循环上运行一个简单的测试，看看哪个本身更快，因为我的项目将循环数百万个对象。此测试使用1百万个对象填充List，每个对象都具有MyClass.Age属性。我循环遍历每个对象并拉出Age属性。我在Foreach循环和For循环中执行此操作。有人可以解释一下奇怪的结果，或者告诉我，我犯了一个愚蠢的错误......谢谢

    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;
        }
    }

结果：

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

Answer 1

您应该使用System.Diagnostic.StopWatch课程，而不是使用DateTime.Now进行适当的时间比较

Foreach vs For循环奇怪的结果

1 个答案: