FreeTDS Development Group

["Lowden, James K" <LowdenJK AT bernstein.com>]

> From: Thompson, Bill D (London) [mailto:ThompBil AT exchange.uk.ml.com]
> Sent: August 5, 2003 5:45 AM
> 
> The "destlen" we set to -1 , if the bindlen passed via dbbind() was 0.
> This "destlen" gets passed to dbconvert().
> Unfortunately a destlen of -1 is instructing dbconvert to add 
> a terminating
> NULL to the converted data (which of course ends up 
> overwriting some of your program storage)
> 
> I suppose the problem really lies in our use of dbconvert() 
> to do the work
> of physically copying the data to the target variables. 
> dbconvert has it's external specification which we should 
> stick to, but its
> not *quite* flexible enough for our needs. 
...
> Some alternatives are to :
> 
> a) replace the call to dbconvert with bespoke code (most of 
> which would be
> pulled from dbconvert() ) - bad IMHO
> b) add a third special "destlen" value to dbconvert - a bit 
> of work, but too bad a solution IMHO

Well done, Bill.  

Perhaps an elaborate form of (b).  In sybdb.h:

#define DBCONVERT_OUT_BLANK_NULL = -1
#define DBCONVERT_OUT_NOBLANK_NULL = -2
#define DBCONVERT_OUT_NOBLANK_NONULL = -3

Then buffer_transfer_bound_data() becomes:

        switch (curcol->column_bindtype) {
        case STRINGBIND:
                destlen = DBCONVERT_OUT_NOBLANK_NULL;
        break;
        case NTBSTRINGBIND:
                destlen = DBCONVERT_OUT_BLANK_NULL;
                break;
        default:
                if (curcol->column_bindlen == 0)
                        destlen = DBCONVERT_OUT_NOBLANK_NONULL;
                else
                        destlen = curcol->column_bindlen;
                break;
        }

and dbconvert() of course follows suit.  

This way we don't have to keep looking up what -1 means, and if Sybase
decides to use -3 for something, we can redefine
DBCONVERT_OUT_NOBLANK_NONULL.  We avoid writing specialized code and make
dbconvert() slightly more flexible.  It would be considerable more work to
call tds_convert() instead.  

--jkl


> > >   dbcmd(dbproc, "select i1, family from table1 ");
> > >   dbsqlexec(dbproc);
> > >   if(dbresults(dbproc) == SUCCEED) {
> > >     dbbind(dbproc, 1, STRINGBIND, (DBINT)0, (BYTE*) i1);
> > >     dbbind(dbproc, 2, CHARBIND, (DBINT)0, (BYTE*) &family);
> > > 
> > >     dbnextrow(dbproc);
> > >     printf("%s\n", i1);
> > >   }
> > > }
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