yesterday's time

George George

Hello everyone,

I want to get the same time in yesterday, is there any bug in my below code?

My concern is code, _CurrentDate.Now.Day - 1, if current date is 1, 1 minus 1 is zero, not a valid date?


        DateTime _CurrentDate = DateTime.Now;
        DateTime _LastDate = new DateTime(_CurrentDate.Now.Year, _CurrentDate.Now.Month, _CurrentDate.Now.Day - 1, _CurrentDate.Now.Hour, _CurrentDate.Now.Second);

thanks in advance,
George

18 Replies

Know the answer? Post it — somebody with the same question will find it here.

George George18y ago
Thanks Ryan!

I agree with you. But my question is, what operations are performned when DateTime.Now.Year is executed. I think the following 2 operations are performed, correct?

1. DateTime.Now will create a new temporary instance;

2. Year non-static property is called/retrieved on the new temporary instance.

regards,

George
Ryan Alford18y ago
You are correct that DateTime.Now is a static property and .Year is not a static property. But that is not the issue here. You were trying to use "DateTime.Now.Year" with an instance of the DateTime object, which won't work because the "Now" property is not available to an instance of the DateTime object.

There are two ways to get the current year:

int year = DateTime.Now.Year;
_______________________________________

DateTime currentDate = DateTime.Now;
int year = currentDate.Year;

As you can see, I did NOT do this:

DateTime currentDate = DateTime.Now;
int year = currentDate.Now.Year;

The reason is because ".Now.Year" is not a valid property for a instance of the DateTime object.
George George18y ago
Any comments to my above reply to Ryan?

regards,

George
maveric18y ago
That was a really cool tip thanx for that :)
George George18y ago
Thanks Ryan!

I have checked some internal code. Now is static property and Year is not static property. I think the operation DateTime.Now.Year performs the following opeations,

1. DateTime.Now will create a new temporary instance;

2. Year is called/retrieved on the new temporary instance.

Correct?

regards,

George
Ryan Alford18y ago
I am not sure if it is only a C# specific rule, since I only use C#. But I would think that it is a .Net framework-wide rule.
George George18y ago
Thanks Ryan,

Is it a C# language Spec rule? Any property of a static property is static?

regards,

George
Ryan Alford18y ago
since DateTime.Now is static, any property of it is also static.
George George18y ago
Thanks Ryan,

You are correct. I have checked DateTime.Now is static, but whether DateTime.Now.Year is static or not? Why?

regards,

George
Ryan Alford18y ago
there is no way that the following statement will run in VS2008 without errors:

int year = _CurrentDate.Now.Year;

the reason is that ".Now.Year" is a static member of the DateTime class which means it can't be accessed using an instace of the DateTime class(_CurrentDate is an instance of the DateTime class).

therefore:

DateTime _LastDate = new DateTime(_CurrentDate.Now.Year, _CurrentDate.Now.Month, _CurrentDate.Now.Day - 1, _CurrentDate.Now.Hour, _CurrentDate.Now.Second);

will throw the error:
"Static member 'System.DateTime.Now.get' cannot be accessed with an instance reference; qualify it with a type name instead" for everything in bold.
George George18y ago
Thanks Ryan,

I did some tests and maybe my testing is not enough.

1.

You mentioned -- "and since it's obvious you didn't write the original post's code in Visual Studio, when you create an instance of DateTime, you do not have access to the ".Now" property." could you say in other words please? What means "do not have access to ..."?

2.

"so your, "_currentDate.Now.Year", would have thrown exceptions." -- which statement do you mean will generate exceptions? I have tested again in Visual Studio 2008, it runs ok. Please feel free to point my mistake.

regards,

George
Ryan Alford18y ago
and since it's obvious you didn't write the original post's code in Visual Studio, when you create an instance of DateTime, you do not have access to the ".Now" property.

so your, "_currentDate.Now.Year", would have thrown exceptions.

I am still wondering why you asked your first question. a simple copy/paste into Visual Studio, then running(after fixing the .Now errors), it would have thrown an error saying that the month, day, year parameters are not a valid date.

Please, download Visual Studio 2008 Express Edition. IT IS FREE. Then take some of this code, and TEST IT YOURSELF.
George George18y ago
Thanks nilanka dharmadasa,

Your solution works.

regards,

George
Nilanka Dharmadasa18y ago
Or it can be done in one line like this.

DateTime yesterdaytime = DateTime.Now.AddDays(-1);
George George18y ago
Thanks, man!

Question answered.

regards,

George
Jan Montano18y ago
the Date property returns the date component.

if (date1.Date != date2.Date)
George George18y ago
Cool, Jan!

A harder question for you, how to check if two DateTime type instance is in the same date?

(example, 8am and 9am of yesterday belong to the same date, but 11:30pm from yesterday to 0:30am today, even if just elapse one hour, they do not belong to the same date.)

regards,

George
Jan Montano18y ago
You could also try this one:

TimeSpan oneDay = new TimeSpan(1,0,0,0);
DateTime yesterday = DateTime.Now.Subtract(oneDay);