在关注性能时，对DateTime.Today使用变量有多重要？ [英] How important is it to use a variable for DateTime.Today when concerned about performance?

问题描述

我刚刚看到这个被高调的评论

IIRC DateTime.Today 是一个相当昂贵的调用，所以你最好先将值存储在变量中。

IIRC DateTime.Today is a quite expensive call, so you better store the value in a variable first.

这是为了回应一个包含代码的帖子： p>

It was in response to a post that contained the code:

var first = 
    new DateTime(DateTime.Today.Year, DateTime.Today.Month, 1).AddMonths(-1);
var last = 
    new DateTime(DateTime.Today.Year, DateTime.Today.Month, 1).AddDays(-1);

如果我希望提高性能，请保存 DateTime .Today 在一个变量中，而不是多次调用它？大概有多少使用 DateTime.Today 可以为它创建一个变量？

If I am looking to improve performance, how important is it to store DateTime.Today in a variable instead of calling it multiple times? And roughly how many uses of DateTime.Today would justify creating a variable for it?

编辑： 我意识到我应该测试我的程序，看看是否有性能问题，首先是担心这样的微不足道的事情。为了这个问题，假设我已经做了这个，并且确定需要额外的优化。

I realize I should test my program to see if there are performance problems first before worrying about something as trivial as this. For the sake of this question, assume that I have already done this and determined that additional optimization is needed.

推荐答案

基准我的机器，使用Stopwatch类）：

Benchmark (on my machine, using the Stopwatch class):

10,000 DateTime.Today calls and assignment to local variable: 0.0125781 seconds.

10,000 Assignment only operations: 0.0001062 seconds.

代码：

var s = new Stopwatch();
DateTime date = DateTime.Today;
DateTime date2 = DateTime.Today;
s.Start();
for (int i=0; i<10000; i++)
    date = DateTime.Today;
s.Stop();
Debug.Print(s.Elapsed.ToString());

s.Reset();
s.Start();
for (int i=0; i<10000; i++)
    date2 = date;
s.Stop();
Debug.Print(s.Elapsed.ToString());

这篇关于在关注性能时，对DateTime.Today使用变量有多重要？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！