DateTime.Add() query

5 Jul 2006 10:07 AM

madhur

Hello

If I create a DateTime instance like this :
DateTime d=DateTime.Now();
And then
d.AddDays(3);

The 3 days doesnt get added to it. But If I do like this :

DateTime d=DateTime.Now.AddDays(4);

The days gets added correctly.

Can anyone explain me the behaviour ??

Madhur

5 Jul 2006 10:31 AM

Larry Lard

madhur wrote:
Show quote

> Hello
>
> If I create a DateTime instance like this :
> DateTime d=DateTime.Now();
> And then
> d.AddDays(3);
>
> The 3 days doesnt get added to it. But If I do like this :
>
> DateTime d=DateTime.Now.AddDays(4);
>
> The days gets added correctly.
>
> Can anyone explain me the behaviour ??

..AddDays is a _function_ that returns the _new_ value, not a method
that changes the existing value. Thus when you do

d.AddDays(3);

you are saying: Take the value of d, add three days to it, then do
nothing with the result. The three days does get added to it; but the
result is then thrown away.

But when you say

d=DateTime.Now.AddDays(4);

you are saying: Take the value of DateTime.Now, add four days to it,
and _assign the resulting value to d_.

If you want to change d from its current value to (its current value
plus three days), you should say

d = d.AddDays(3);

--
Larry Lard
Replies to group please

5 Jul 2006 11:04 AM

ValliM

Hi Madhur,

You have added 3 days to d, but you did not store the value to any variable.
So as intialized in the first step d has the present time alone.
Moreover you have used DateTime.Now(), Now is the property but it is used
like a method.

This might work correctly.
DateTime d = DateTime.Now;

d=d.AddDays(3);

Regards,

Valli.

www.syncfusion.com

Show quote

"madhur" <ahuja.mad***@gmail.com> wrote in message
news:1152094027.207026.48770@a14g2000cwb.googlegroups.com...
> Hello
>
> If I create a DateTime instance like this :
> DateTime d=DateTime.Now();
> And then
> d.AddDays(3);
>
> The 3 days doesnt get added to it. But If I do like this :
>
> DateTime d=DateTime.Now.AddDays(4);
>
> The days gets added correctly.
>
> Can anyone explain me the behaviour ??
>
> Madhur
>

5 Jul 2006 6:17 PM

Jon Skeet [C# MVP]

madhur <ahuja.mad***@gmail.com> wrote:

> If I create a DateTime instance like this :
> DateTime d=DateTime.Now();
> And then
> d.AddDays(3);
>
> The 3 days doesnt get added to it. But If I do like this :
>
> DateTime d=DateTime.Now.AddDays(4);
>
> The days gets added correctly.
>
> Can anyone explain me the behaviour ??

Whenever something surprising happens, it's best to consult the
documentation. Here's part of what MSDN says about DateTime.AddDays in
the "Remarks" section:

<quote>
This method does not change the value of this DateTime. Instead, a new
DateTime is returned whose value is the result of this operation.
</quote>

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too

5 Jul 2006 6:45 PM

Madhur

Jon Skeet [C# MVP] wrote:
Show quote

> madhur <ahuja.mad***@gmail.com> wrote:
>> If I create a DateTime instance like this :
>> DateTime d=DateTime.Now();
>> And then
>> d.AddDays(3);
>>
>> The 3 days doesnt get added to it. But If I do like this :
>>
>> DateTime d=DateTime.Now.AddDays(4);
>>
>> The days gets added correctly.
>>
>> Can anyone explain me the behaviour ??
>
> Whenever something surprising happens, it's best to consult the
> documentation. Here's part of what MSDN says about DateTime.AddDays in
> the "Remarks" section:
>
> <quote>
> This method does not change the value of this DateTime. Instead, a new
> DateTime is returned whose value is the result of this operation.
> </quote>

Thanks to all those who replied. Indeed I should have consulted the
documentation first.

--
Madhur Ahuja