Logical field: false (.f.) vs Null

[fox26apgmr]

Hi,
Is there a way to test if a logical field actually contains the false setting versus defaulting to false because it is null?
Thanks, Joe

 

[rgbean]

FoxPro for DOS and Windows don't support "null", although VFP does. Logicals can only be .T. or .F. if it's not true, it's false!

Rick

 

[udaisengupta]

Joe,
Try using the ISBLANK(fieldname) function to validate whether that particular field actually contains the false setting versus defaulting to false because it is null.
I also had the same problem and i received help from this forum on this count.



Best Regards,
Yours sincerely,
Udai.

 

[fox26apgmr]

Thanks Udai, that works great!

 

[wgcs]

Just for the record, you might notice here that there are 3 states a field can have (in VFP), two of those states used to exist in FPDos:

Blank - Hasn't been filled in yet (use ISBLANK() to check)
Null - Is marked as having No data (use ISNULL() to check)
Something - May be spaces, or whatever values are valid for the field's data type. You can see if it's spaces/tabs using EMPTY()

So:
ISNULL( .NULL. ) = .T.
ISBLANK( .NULL. ) = .F.
EMPTY( .NULL. ) = .F.

Tbl.Fld is a "blank" field:
ISNULL( tbl.Fld ) = .F.
ISBLANK( tbl.Fld ) = .T.
EMPTY( tbl.Fld ) = .T.

Tbl.Fld = 0 or spaces:
ISNULL( tbl.Fld ) = .F.
ISBLANK( tbl.Fld ) = .F.
EMPTY( tbl.Fld ) = .T.

Tbl.Fld <>0 or has some characters:
ISNULL( tbl.Fld ) = .F.
ISBLANK( tbl.Fld ) = .F.
EMPTY( tbl.Fld ) = .F.