null == int testing

[cmay]

In VB you can test if a value type has the "default" value by doing the
following:

dim i as integer
if (Nothing = i) then
'* i is really 0
end if


Now, when I try to do this in C# of course it doesn't work because you can't
do:

int i;
if ( null == i) {
// i is 0
}

of course because you can't compare null == i.

Now, in this case I know, and you know, that an int defaults to 0, but there
are lots of types that default to some value that I don't know, e.g.
System.Drawing. Color.

Can anyone tell me how I can check if a value type is equal to its default
value?

[jeremiah johnson]

Re: null == int testing

You know you have an int, why don't you just set it to 0 when you create it?

int i = 0;

That way you know exactly what you're working with.

jeremiah();

cmay wrote:[color=blue]
> In VB you can test if a value type has the "default" value by doing the
> following:
>
> dim i as integer
> if (Nothing = i) then
> '* i is really 0
> end if
>
>
> Now, when I try to do this in C# of course it doesn't work because you can't
> do:
>
> int i;
> if ( null == i) {
> // i is 0
> }
>
> of course because you can't compare null == i.
>
> Now, in this case I know, and you know, that an int defaults to 0, but there
> are lots of types that default to some value that I don't know, e.g.
> System.Drawing. Color.
>
> Can anyone tell me how I can check if a value type is equal to its default
> value?[/color]

[jeremiah johnson]

Re: null == int testing

to re-answer your question, since i misread it last time, i'll say that
the C# compiler, in every circumstance I have ever come across, will
always assign a sensible default value when you declare an integer.

if you have i declared at one point, and you mistakenly redeclare it,
you'll get a warning from the compiler.

just set all of your variables to some value that makes sense on creation.

also in C# i believe that you must do

if (i == null) {}

rather than

if (null == i) {}

as you have shown, but i'm not sure.

cmay wrote:[color=blue]
> In VB you can test if a value type has the "default" value by doing the
> following:
>
> dim i as integer
> if (Nothing = i) then
> '* i is really 0
> end if
>
>
> Now, when I try to do this in C# of course it doesn't work because you can't
> do:
>
> int i;
> if ( null == i) {
> // i is 0
> }
>
> of course because you can't compare null == i.
>
> Now, in this case I know, and you know, that an int defaults to 0, but there
> are lots of types that default to some value that I don't know, e.g.
> System.Drawing. Color.
>
> Can anyone tell me how I can check if a value type is equal to its default
> value?[/color]

[Ted Miller]

Re: null == int testing

This may or may not help you now, but in C# 2.0 you can do

if (i == default(int)) ...

Also, your canned example -- even if altered to compare against 0, such as
"if (i == 0)" -- wouldn't even compile, because C# does not allow use of
uninitialized variables.

PS the idiom of putting the constant on the left-hand side of a comparison
is not needed in C#, because there is no implicit conversion to bool from
other types like there is in C/C++.


"cmay" <cmay@discussio ns.microsoft.co m> wrote in message
news:8E7FD3BD-7C17-4167-8FE0-F76A3E748AC7@mi crosoft.com...[color=blue]
> In VB you can test if a value type has the "default" value by doing the
> following:
>
> dim i as integer
> if (Nothing = i) then
> '* i is really 0
> end if
>
>
> Now, when I try to do this in C# of course it doesn't work because you
> can't
> do:
>
> int i;
> if ( null == i) {
> // i is 0
> }
>
> of course because you can't compare null == i.
>
> Now, in this case I know, and you know, that an int defaults to 0, but
> there
> are lots of types that default to some value that I don't know, e.g.
> System.Drawing. Color.
>
> Can anyone tell me how I can check if a value type is equal to its default
> value?[/color]

[cody]

Re: null == int testing

You can test if (i==new int()) or if (i==new MyStruct())

The default constructor of a value type will always return a
null-initialized struct.

"cmay" <cmay@discussio ns.microsoft.co m> schrieb im Newsbeitrag
news:8E7FD3BD-7C17-4167-8FE0-F76A3E748AC7@mi crosoft.com...[color=blue]
> In VB you can test if a value type has the "default" value by doing the
> following:
>
> dim i as integer
> if (Nothing = i) then
> '* i is really 0
> end if
>
>
> Now, when I try to do this in C# of course it doesn't work because you
> can't
> do:
>
> int i;
> if ( null == i) {
> // i is 0
> }
>
> of course because you can't compare null == i.
>
> Now, in this case I know, and you know, that an int defaults to 0, but
> there
> are lots of types that default to some value that I don't know, e.g.
> System.Drawing. Color.
>
> Can anyone tell me how I can check if a value type is equal to its default
> value?[/color]

[Ted Miller]

Re: null == int testing

This only works for value types that implement operator ==. It does not
compile in the general case.

"cody" <deutronium@gmx .de> wrote in message
news:ucY9w%23ub FHA.3280@TK2MSF TNGP09.phx.gbl. ..[color=blue]
> You can test if (i==new int()) or if (i==new MyStruct())
>
> The default constructor of a value type will always return a
> null-initialized struct.
>
> "cmay" <cmay@discussio ns.microsoft.co m> schrieb im Newsbeitrag
> news:8E7FD3BD-7C17-4167-8FE0-F76A3E748AC7@mi crosoft.com...[color=green]
>> In VB you can test if a value type has the "default" value by doing the
>> following:
>>
>> dim i as integer
>> if (Nothing = i) then
>> '* i is really 0
>> end if
>>
>>
>> Now, when I try to do this in C# of course it doesn't work because you
>> can't
>> do:
>>
>> int i;
>> if ( null == i) {
>> // i is 0
>> }
>>
>> of course because you can't compare null == i.
>>
>> Now, in this case I know, and you know, that an int defaults to 0, but
>> there
>> are lots of types that default to some value that I don't know, e.g.
>> System.Drawing. Color.
>>
>> Can anyone tell me how I can check if a value type is equal to its
>> default
>> value?[/color]
>
>[/color]

[Daniel O'Connell [C# MVP]]

Re: null == int testing

> also in C# i believe that you must do[color=blue]
>
> if (i == null) {}
>
> rather than
>
> if (null == i) {}
>
> as you have shown, but i'm not sure.
>[/color]


Either is perfectly acceptable, the reasoning for null == i is just no
longer there.

[Jon Skeet [C# MVP]]

Re: null == int testing

Ted Miller <ted@millerzone .net> wrote:[color=blue]
> This only works for value types that implement operator ==. It does not
> compile in the general case.[/color]

True. Change it to:

if (i.Equals(new MyStruct())) and it works fine though.

--
Jon Skeet - <skeet@pobox.co m>

http://www.pobox.com/~skeet

If replying to the group, please do not mail me too

[Sherif El-Metainy]

Re: null == int testing

Then we can use Object.Equals, which will suffer performance penalties
becaue of boxing

Best regards,
Sherif
"Ted Miller" <ted@millerzone .net> wrote in message
news:11an7vh2h3 42df4@corp.supe rnews.com...[color=blue]
> This only works for value types that implement operator ==. It does not
> compile in the general case.
>
> "cody" <deutronium@gmx .de> wrote in message
> news:ucY9w%23ub FHA.3280@TK2MSF TNGP09.phx.gbl. ..[color=green]
>> You can test if (i==new int()) or if (i==new MyStruct())
>>
>> The default constructor of a value type will always return a
>> null-initialized struct.
>>
>> "cmay" <cmay@discussio ns.microsoft.co m> schrieb im Newsbeitrag
>> news:8E7FD3BD-7C17-4167-8FE0-F76A3E748AC7@mi crosoft.com...[color=darkred]
>>> In VB you can test if a value type has the "default" value by doing the
>>> following:
>>>
>>> dim i as integer
>>> if (Nothing = i) then
>>> '* i is really 0
>>> end if
>>>
>>>
>>> Now, when I try to do this in C# of course it doesn't work because you
>>> can't
>>> do:
>>>
>>> int i;
>>> if ( null == i) {
>>> // i is 0
>>> }
>>>
>>> of course because you can't compare null == i.
>>>
>>> Now, in this case I know, and you know, that an int defaults to 0, but
>>> there
>>> are lots of types that default to some value that I don't know, e.g.
>>> System.Drawing. Color.
>>>
>>> Can anyone tell me how I can check if a value type is equal to its
>>> default
>>> value?[/color]
>>
>>[/color]
>
>[/color]

[Jon Skeet [C# MVP]]

Re: null == int testing

<"Sherif El-Metainy" <elmeteny REMOVETHIS at thewayout NOSPAM dot
net>> wrote:[color=blue]
> Then we can use Object.Equals, which will suffer performance penalties
> becaue of boxing[/color]

Using Object.Equals doesn't so much suffer performance penalties
because of boxing, but because the implementation of ValueType.Equal s
uses reflection to compare the value of each field in turn.

--
Jon Skeet - <skeet@pobox.co m>

http://www.pobox.com/~skeet

If replying to the group, please do not mail me too

[Bob Grommes]

Re: null == int testing

I would have to check to be sure, but I don't believe that "if Nothing = i"
works in VB.NET either unless you have Option Strict Off. Which you never
should.

An int is a value type and as such can never equal null (or Nothing in VB
parlance).

In any case if it equals zero, then it does not and can not equal something
else, such as null.

This is the sort of muddled thinking that turns me off to VB. A default
value is not an unknown value and the two should never be confused.

--Bob

"cmay" <cmay@discussio ns.microsoft.co m> wrote in message
news:8E7FD3BD-7C17-4167-8FE0-F76A3E748AC7@mi crosoft.com...[color=blue]
> In VB you can test if a value type has the "default" value by doing the
> following:
>
> dim i as integer
> if (Nothing = i) then
> '* i is really 0
> end if
>
>
> Now, when I try to do this in C# of course it doesn't work because you
> can't
> do:
>
> int i;
> if ( null == i) {
> // i is 0
> }
>
> of course because you can't compare null == i.
>
> Now, in this case I know, and you know, that an int defaults to 0, but
> there
> are lots of types that default to some value that I don't know, e.g.
> System.Drawing. Color.
>
> Can anyone tell me how I can check if a value type is equal to its default
> value?[/color]

[Jon Skeet [C# MVP]]

Re: null == int testing

Bob Grommes <bob@bobgrommes .com> wrote:[color=blue]
> I would have to check to be sure, but I don't believe that "if Nothing = i"
> works in VB.NET either unless you have Option Strict Off. Which you never
> should.[/color]

Yes it does. Try this:

Option Strict On
Imports System

Public Class Test

Shared Sub Main()
Dim x as Integer = Nothing
Console.WriteLi ne(x)
End Sub
End Class

[color=blue]
> An int is a value type and as such can never equal null (or Nothing in VB
> parlance).[/color]

Nothing is somewhat overloaded in VB.NET - it means the default value
for any type, so null, 0, false, '\0' or a struct with every field set
to the default value for its type.

--
Jon Skeet - <skeet@pobox.co m>

http://www.pobox.com/~skeet

If replying to the group, please do not mail me too

[cody]

Re: null == int testing

I have to wonder why the default implementation doesn't do a bitwise binary
comparison of the struct like C's memcmp()? For reference types in the
default implementation only the reference is tested for bitwise equality,
and not the reflected fields are compared using Equals().


"Jon Skeet [C# MVP]" <skeet@pobox.co m> schrieb im Newsbeitrag
news:MPG.1d15e7 834ac4315798c2d 5@msnews.micros oft.com...[color=blue]
> <"Sherif El-Metainy" <elmeteny REMOVETHIS at thewayout NOSPAM dot
> net>> wrote:[color=green]
>> Then we can use Object.Equals, which will suffer performance penalties
>> becaue of boxing[/color]
>
> Using Object.Equals doesn't so much suffer performance penalties
> because of boxing, but because the implementation of ValueType.Equal s
> uses reflection to compare the value of each field in turn.
>
> --
> Jon Skeet - <skeet@pobox.co m>
> http://www.pobox.com/~skeet
> If replying to the group, please do not mail me too[/color]

[Jon Skeet [C# MVP]]

Re: null == int testing

cody <deutronium@gmx .de> wrote:[color=blue]
> I have to wonder why the default implementation doesn't do a bitwise binary
> comparison of the struct like C's memcmp()? For reference types in the
> default implementation only the reference is tested for bitwise equality,
> and not the reflected fields are compared using Equals().[/color]

I think it does a bitwise binary comparison in some cases, but uses
Equals() to compare fields if any of the fields override Equals - so if
your struct contains a string reference, two distinct references to
equal strings in two instances of the struct won't stop those instances
from being equal.

--
Jon Skeet - <skeet@pobox.co m>

http://www.pobox.com/~skeet

If replying to the group, please do not mail me too

[cmay]

Re: null == int testing

Thanks everyone.

I was sure that I had tried:
if (new System.Drawing. Color() == MyColor)

But I must not have because it works like I wanted it to.

Thanks!