RE: Null Capable Fields

[boothm@xxxxxxxxxxxxxxxxx]

ok, my curioisty is piqued.  What problem does a "null-capable" field 
solve?  I thought it's only function was to signal a data field's 
virginity, and I can't imagine a problem that solves.

btw, please be gentle as you explain my idiocy, ok?

 


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Subject:        RE: Null Capable Fields

Brian,
I think that null support is only for database fields.

As for workarounds, I think you'll have to add a "null indicator" field 
that
you will manipulate "on the side" so to speak.  An alternative is to 
create
a dummy database file containing fields defined as null capable.  Define
this dummy file as input only, user controlled open and don't open it. 
This
will allow you to create as many null capable work fields as you need.

If you're just getting into null support, check out the RPG Reference
manual's section on Database Null Value Support.  I'll push my luck and 
post
a section that will probably spark another "Why did IBM do it this way?"
thread.

"You are responsible for ensuring that fields containing null values are
used correctly within the program. For example, if you use a null-capable
field as factor 2 of a MOVE operation, you should first check if it is 
null
before you do the MOVE, otherwise you may corrupt your result field value.
You should also be careful when outputting a null-capable field to a file
that does not have the field defined as null-capable, for example a 
WORKSTN
or PRINTER file, or a program-described file.
 
Note:  The value of the null indicator for a null-capable field is only
considered for these operations: input, output and file-positioning. Here
are some examples of operations where the null indicator is not taken into
consideration:
 
DSPLY of a null-capable field shows the contents of the field even if the
null indicator is on.
 
If you move a null-capable field to another null-capable field, and the
factor 2 field has the null indicator on, the result field will get the 
data
from the factor 2 field. The corresponding null indicator for the result
field will not be set on.
 
Comparison operations, including SORTA and LOOKUP, with null capable 
fields
do not consider the null indicators."

Hope this helps,

Buck Calabro
Aptis; Albany, NY
mailto:Buck.Calabro@aptissoftware.com

> -----Original Message-----
> From:          bellis@ORIENTAL.COM 
> Sent:          Monday, October 11, 1999 4:01 PM
> To:            RPG400-L@midrange.com
> Subject:               Null Capable Fields
> 
> We have fields within DB2 files defined as "Null Capable".
> 
> Within an RPG IV program we try to define fields using the "like" 
keyword
> over
> these null capable fields, or define fields using externally described
> data
> structures over the file with null capable fields.
> However, none of these fields defined internally to the RPG program keep
> the
> null capable attribute.
> i.e.   I cannot use the %NULLIND BIF on the field.
> 
> Here is a excerpt from the on-line AS/400 reference books (V4R4) on this
> subject:
> "If the file used for an externally described data structure has
> null-capable
> fields defined, the null attribute is not used in defining the RPG
> subfield."
> 
> Is there a way to define fields internal to RPG programs as null 
capable?
> If not, is there a work around for this?
> 
> Thanks,
> Brian Ellis.
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