yesterday's time

Question

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

George George · Answer

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 Alford · Answer

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 George · Answer

Any comments to my above reply to Ryan? regards George

maveric · Answer

That was a really cool tip thanx for that :)

George George · Answer

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 Alford · Answer

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 George · Answer

Thanks Ryan Is it a C# language Spec rule? Any property of a static property is static? regards George

Ryan Alford · Answer

since DateTime.Now is static any property of it is also static.

George George · Answer

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 Alford · Answer

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 George · Answer

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 Alford · Answer

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 George · Answer

Thanks nilanka dharmadasa Your solution works. regards George

Nilanka Dharmadasa · Answer

Or it can be done in one line like this. DateTime yesterdaytime = DateTime .Now.AddDays(-1);

George George · Answer

Thanks man! Question answered. regards George

Jan Montano · Answer

the Date property returns the date component. if (date1.Date != date2.Date)

George George · Answer

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 Montano · Answer

You could also try this one: TimeSpan oneDay = new TimeSpan(1000); DateTime yesterday = DateTime.Now.Subtract(oneDay);