<s>
The	O
Is	B-Language
functions	I-Language
(	O
also	O
known	O
as	O
data	O
information	O
functions	O
,	O
data	O
inspection	O
functions	O
,	O
or	O
data-testing	O
functions	O
)	O
are	O
a	O
set	O
of	O
functions	O
in	O
Microsoft	O
's	O
Visual	B-Language
Basic	I-Language
6	I-Language
,	O
Visual	B-Language
Basic	I-Language
for	I-Language
Applications	I-Language
,	O
VBScript	B-Application
,	O
and	O
Visual	B-Language
Basic	I-Language
.NET	I-Language
.	O
</s>
<s>
Several	O
of	O
them	O
are	O
also	O
provided	O
in	O
Transact-SQL	B-Language
by	O
the	O
.NET	B-Application
Framework	I-Application
Data	O
Provider	O
for	O
Microsoft	B-Application
SQL	I-Application
Server	I-Application
.	O
</s>
<s>
In	O
Transact-SQL	B-Language
,	O
the	O
functions	O
return	O
zero	O
or	O
one	O
rather	O
than	O
Boolean	O
values	O
True	O
and	O
False	O
.	O
</s>
<s>
Uninitialized	O
arrays	O
will	O
,	O
note	O
,	O
return	O
False	O
from	O
this	O
function	O
in	O
Visual	B-Language
Basic	I-Language
.NET	I-Language
.	O
</s>
<s>
In	O
Visual	B-Language
Basic	I-Language
6	I-Language
,	O
arrays	O
are	O
not	O
reference	O
types	O
,	O
and	O
an	O
uninitialized	O
array	O
will	O
return	O
True	O
from	O
this	O
function	O
just	O
like	O
an	O
initialized	O
array	O
.	O
</s>
<s>
Uninitialized	B-Error_Name
variables	I-Error_Name
that	O
are	O
of	O
type	O
Date	O
can	O
of	O
course	O
be	O
converted	O
,	O
despite	O
being	O
uninitialized	O
,	O
so	O
this	O
will	O
always	O
return	O
True	O
for	O
such	O
variables	O
.	O
</s>
<s>
In	O
VBScript	B-Application
and	O
Visual	B-Language
Basic	I-Language
.NET	I-Language
,	O
the	O
conversion	O
process	O
employs	O
the	O
locale	O
settings	O
of	O
Microsoft	O
Windows	O
,	O
meaning	O
that	O
what	O
may	O
parse	O
as	O
a	O
date	O
on	O
one	O
system	O
,	O
configured	O
to	O
use	O
one	O
locale	O
,	O
may	O
fail	O
to	O
parse	O
as	O
a	O
date	O
on	O
another	O
system	O
,	O
configured	O
to	O
use	O
a	O
different	O
locale	O
.	O
</s>
<s>
This	O
is	O
equivalent	O
to	O
Visual	B-Language
Basic	I-Language
6	I-Language
's	O
IsNull( )	O
function	O
.	O
</s>
<s>
IsDBNull( )	O
is	O
the	O
only	O
way	O
to	O
test	O
for	O
equality	O
to	O
System.DBNull	O
.	O
</s>
<s>
This	O
function	O
was	O
available	O
in	O
Visual	B-Language
Basic	I-Language
6	I-Language
,	O
but	O
has	O
been	O
superseded	O
in	O
Visual	B-Language
Basic	I-Language
.NET	I-Language
by	O
the	O
IsNothing( )	O
function	O
.	O
</s>
<s>
In	O
VBScript	B-Application
,	O
if	O
a	O
variant	O
is	O
assigned	O
Nothing	O
,	O
this	O
function	O
still	O
returns	O
False	O
.	O
</s>
<s>
This	O
function	O
,	O
in	O
Visual	B-Language
Basic	I-Language
.NET	I-Language
,	O
determines	O
whether	O
the	O
expression	O
passed	O
as	O
its	O
argument	O
is	O
an	O
exception	O
object	O
,	O
i.e.	O
</s>
<s>
In	O
Visual	B-Language
Basic	I-Language
6	I-Language
,	O
the	O
function	O
tests	O
whether	O
the	O
expression	O
is	O
a	O
variant	O
with	O
the	O
special	O
vbError	O
subtype	O
.	O
</s>
<s>
This	O
function	O
only	O
exists	O
in	O
Visual	B-Language
Basic	I-Language
6	I-Language
.	O
</s>
<s>
In	O
Visual	B-Language
Basic	I-Language
.NET	I-Language
,	O
optional	O
parameters	O
are	O
required	O
to	O
have	O
default	O
initializers	O
,	O
and	O
the	O
function	O
no	O
longer	O
exists	O
.	O
</s>
<s>
It	O
is	O
a	O
simple	O
library	O
function	O
(	O
comprising	O
just	O
4	O
CIL	O
instructions	O
)	O
which	O
can	O
itself	O
be	O
written	O
in	O
Visual	B-Language
Basic	I-Language
as	O
:	O
The	O
effect	O
of	O
this	O
is	O
to	O
return	O
False	O
for	O
all	O
value	O
(	O
non-reference	O
)	O
expressions	O
,	O
because	O
they	O
will	O
be	O
wrapped	O
up	O
,	O
as	O
part	O
of	O
the	O
function	O
call	O
,	O
into	O
objects	O
,	O
which	O
will	O
by	O
their	O
very	O
natures	O
,	O
not	O
be	O
null	O
objects	O
.	O
</s>
<s>
To	O
avoid	O
this	O
behaviour	O
,	O
one	O
can	O
use	O
the	O
IS	O
operator	O
to	O
compare	O
an	O
object	O
directly	O
to	O
Nothing	O
,	O
writing	O
expression	O
rather	O
than	O
IsNothing(expression )	O
.	O
</s>
<s>
Strings	O
are	O
reference	O
types	O
in	O
Visual	B-Language
Basic	I-Language
.NET	I-Language
,	O
and	O
so	O
capable	O
of	O
being	O
null	O
(	O
as	O
opposed	O
to	O
simply	O
zero-length	O
,	O
empty	O
,	O
strings	O
)	O
.	O
</s>
<s>
This	O
function	O
,	O
taking	O
two	O
arguments	O
,	O
is	O
specific	O
to	O
Transact-SQL	B-Language
.	O
</s>
<s>
In	O
contrast	O
to	O
the	O
Visual	B-Language
Basic	I-Language
function	O
by	O
this	O
name	O
,	O
it	O
does	O
not	O
return	O
a	O
Boolean	O
,	O
but	O
instead	O
returns	O
the	O
first	O
expression	O
if	O
that	O
is	O
not	O
NULL	O
,	O
otherwise	O
the	O
second	O
expression	O
.	O
</s>
<s>
In	O
Transact-SQL	B-Language
,	O
strings	O
can	O
be	O
converted	O
to	O
numbers	O
even	O
if	O
they	O
contain	O
characters	O
that	O
one	O
might	O
not	O
expect	O
in	O
numbers	O
.	O
</s>
<s>
This	O
is	O
because	O
Transact-SQL	B-Language
allows	O
conversion	O
from	O
money	O
and	O
smallmoney	O
types	O
to	O
numbers	O
,	O
and	O
monetary	O
data	O
in	O
string	O
form	O
may	O
contain	O
currency	O
indicator	O
characters	O
such	O
as	O
the	O
'	O
£	O
 '	O
or	O
'	O
$	O
 '	O
symbols	O
.	O
</s>
<s>
The	O
same	O
is	O
true	O
of	O
VBScript	B-Application
,	O
where	O
any	O
string	O
that	O
can	O
be	O
converted	O
to	O
a	O
currency	O
value	O
in	O
the	O
current	O
locale	O
is	O
considered	O
to	O
be	O
numeric	O
.	O
</s>
<s>
VBScript	B-Application
does	O
not	O
,	O
however	O
,	O
consider	O
dates	O
and	O
times	O
to	O
be	O
numeric	O
.	O
</s>
<s>
This	O
is	O
equivalent	O
to	O
Visual	B-Language
Basic	I-Language
.NET	I-Language
'	O
s	O
IsReference( )	O
function	O
.	O
</s>
<s>
This	O
is	O
equivalent	O
to	O
Visual	B-Language
Basic	I-Language
6	I-Language
's	O
IsObject( )	O
function	O
.	O
</s>
