c#赋值的执行顺序

来源：互联网发布：php 整数求余数编辑：程序博客网时间：2024/06/06 00:20

主要代码

有下面一段代码，

/*@Magma 2014/05/22  *This code is testing the performance of boxing */using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace Service{    public class Boxing    {        /// <summary>        /// Test the performance of boxing         /// </summary>        /// <param name="cycleTimes">the times of cycles</param>        /// <returns></returns>        public void PerformanceTest(int cycleTimes) {            //Normal operation            DateTime begin = DateTime.Now;            for (int i = 0; i < cycleTimes; i++)            {                int ita = 63;                //int itb = ita;            }            Console.WriteLine("the time of Normal:" + (DateTime.Now - begin).Seconds + "s," + (DateTime.Now - begin).Milliseconds + "ms");             //boxing            begin = DateTime.Now;                        for (int i = 0; i < cycleTimes; i++)            {                object ob = 1;//inboxing                //int it = (int)ob;//unboxing            }            Console.WriteLine("the time of Boxing:" + (DateTime.Now - begin).Seconds+"s,"+(DateTime.Now - begin).Milliseconds+"ms");         }    }}

循环4000次时

用如下代码调用：

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;using Service;using Model;namespace KindsIntegration{    class Program    {        static void Main(string[] args)        {            Boxing box = new Boxing();            box.PerformanceTest(4000);            Console.ReadLine();        }    }}

输出（反复运行多次）：

这个结果很难理解，装箱操作的时间竟然比普通赋值时间还要短。

在循环次数小于400000次时一直这样，为了消除执行先后的影响，我改变了Performance函数中装箱与普通操作的先后顺序，结果一样（装箱时间<普通赋值）

循环1000000

输出（反复运行多次）：

这个结果比较正常，装箱的时间超过正常赋值

原因：

论坛上有人帮忙回答，结果真是奇怪。原因是下面这一句：

DateTime begin = DateTime.Now;

赋值前，要先计算出等号右边的值，再赋值给左边。在得到 datetime.now后，DateTime begin这是一个新对象，需要创建，时间就是消耗在这上面，改成如下的代码，则会清楚地展示原因：

/*@Magma 2014/05/22  *This code is testing the performance of boxing */using System;namespace Service{    public class Boxing    {        /// <summary>        /// Test the performance of boxing         /// </summary>        /// <param name="cycleTimes">the times of cycles</param>        /// <returns></returns>        public void PerformanceTest(int cycleTimes) {            //Normal operation            DateTime begin = DateTime.Now;            Console.WriteLine("begin:"+begin.Millisecond);            begin = DateTime.Now;            Console.WriteLine("begin:" + begin.Millisecond);            begin = DateTime.Now;            Console.WriteLine("begin:" + begin.Millisecond);            begin = DateTime.Now;            Console.WriteLine("begin:" + begin.Millisecond);            begin = DateTime.Now;            Console.WriteLine("begin:" + begin.Millisecond);            for (int i = 0; i < cycleTimes; i++)            {                int x = 63;                int y = x;            }            Console.WriteLine("the time of Normal:" + (DateTime.Now - begin).Seconds + "s," + (DateTime.Now - begin).Milliseconds + "ms");             //boxing            begin = DateTime.Now;                        for (int i = 0; i < cycleTimes; i++)            {                int x = 1;                object ob = x;//inboxing            }            Console.WriteLine("the time of Boxing:" + (DateTime.Now - begin).Seconds+"s,"+(DateTime.Now - begin).Milliseconds+"ms");         }    }}

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