FreeTDS Development Group

[Brian Bruns <camber AT umcc.ais.org>]

I found this problem.  It affects only TDS 7.0 as you have guessed.

With 7.0, Microsoft introduced long char types (char, varchar, etc...).
These have a two byte (16 bit) length.  For 8 bit length types, NULL is
represented by 0. Problem is you can't tell the difference between a zero
length varchar and a null one (insert '' into a varchar and it is actually
represented by a single space ' ').

So microsoft's (not bad) solution is to to represent NULL with 65355
(0xFFFF or -1 using signed int).  So, here is a little patch to fix
it...in tds_process_row() (token.c):

             } else if (is_large_type(curcol->column_xtype)) {
                      colsize = tds_get_smallint(tds);
+                     if (colsize==-1) colsize=0;
             } else if (!is_fixed_type(curcol->column_type)) {

I also checked it into CVS.

Cheers,

Brian

On Fri, 18 Feb 2000, Bill Doulass wrote:

> I tried downsizing to TDSVER=42, and the NULL problem went away.  I will 
> continue to work with this version for the time being.
> 
> Thanks again, all.
>