[freetds] Empty VARCHAR parameters converted to NULL

Frediano Ziglio freddy77 at gmail.com
Tue Jan 19 05:52:15 EST 2016

2016-01-16 1:41 GMT+00:00 Joshua Lang <joshua.h.lang at gmail.com>:
> In the latest version of FreeTDS-dblib (0.95.79) I'm passing rpc VARCHAR
> parameters of 0 length, but non-NULL (empty strings). FreeTDS seems to turn
> these into NULL values before passing them on to SQL Server. From what I've
> read, it seems as if older databases didn't support passing empty strings,
> but newer ones do? (i.e. TDS 7.0+ do support empty strings).
> It seems as this is a known issue, but I was wondering if it is possible to
> fix it for the newer versions of SQL server? E.g. in dbrpcparam() passing a
> non-NULL pointer to the 'value' parameter and a 0 to 'datalen' would
> indicate an empty string is desired if possible.
> Thoughts?

The main problem is not libTDS (the code library) but dbrpcparam specification.
datalen < 0 is invalid for variable fields (like VARCHAR) and 0 is used for NULL
value (no matter the data pointer). But looks like your suggestion
(not NULL value
and 0 datalen) could be a good choice.
Not sure however if this could work with all types and server versions
(for instance
0 size TEXT).
We can do it but I'm not thinking about backporting it to 0.95.


More information about the FreeTDS mailing list