Null

[Jim Heavey]

Hello, If you have a method which test field to see if it is a valid date
and either returns a DateTime value which either has a valid datetime or it
has null, how can you test if the value returned is null? I tried and I
get an compile error "Can not be applied to operands System.DateTime and
null?

dtStart != null

I also tried the is operator

dtStart is null

but it does not like this either...

Thanks in advance for your assistance!!!!!!!!!!

[José Joye]

DateTime is a value type :-(
In that sense, it cannot be set to null.
The easiest solution is to define a particular date that will act as a null
(eg: minval)

I remember reading a post about this refering a site where you can download
a class implementing DateTime feature.

José

"Jim Heavey" <Ji*******@nospam.com> a écrit dans le message de
news:Xn*********************************@207.46.24 8.16...

Hello, If you have a method which test field to see if it is a valid date
and either returns a DateTime value which either has a valid datetime or it has null, how can you test if the value returned is null? I tried and I
get an compile error "Can not be applied to operands System.DateTime and
null?

dtStart != null

I also tried the is operator

dtStart is null

but it does not like this either...

Thanks in advance for your assistance!!!!!!!!!!

[Jim Heavey]

I figured this one out...

[JR]

Hi,

It doesn't work because DateTime is a structure which in C# is a value type
not a reference type so assigning null to it has no meaning. It's the same
as doing;

int x;
if(x != null) ;

John.
"Jim Heavey" <Ji*******@nospam.com> wrote in message
news:Xn*********************************@207.46.24 8.16...

Hello, If you have a method which test field to see if it is a valid date
and either returns a DateTime value which either has a valid datetime or it has null, how can you test if the value returned is null? I tried and I
get an compile error "Can not be applied to operands System.DateTime and
null?

dtStart != null

I also tried the is operator

dtStart is null

but it does not like this either...

Thanks in advance for your assistance!!!!!!!!!!

[codymanix]

you cannot use null with DateTime but you can do

if (dtStart==DateTime.Empty())

not tested but my guess :)

--
cody

[Freeware, Games and Humor]
www.deutronium.de.vu || www.deutronium.tk

[Jon Skeet [C# MVP]]

codymanix <do*********************@gmx.de> wrote:

you cannot use null with DateTime but you can do

if (dtStart==DateTime.Empty())

not tested but my guess :)

There *is* no DateTime.Empty() method.

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