FreeTDS Development Group

[Joe Losco <joe AT sqpuv.com>]

James K. Lowden wrote:
> Joe Losco wrote:
>   
> > My problem that I've narrowed it down to is with this stub of code
> > if (SYBCHAR != pcol->type) {           
> >                 pcol->size = dbwillconvert(pcol->type, SYBCHAR);
> >             }
> >
> > I've placed  "printf("name:%s type:%d size:%d\n", pcol->name, 
> > pcol->type, pcol->size);" around this piece of code so that I can see 
> > the before and after effects.  In the command line pure C application 
> > dbwillconvert returns the size of the would be data converted to the 
> > correct type.  This then lets the memory be allocated properly in the 
> > later calloc that uses pcol->size+1, as well as everything else to work 
> > as intended. 
> >     
>
> Yes, that's my code.  
>
> db-lib as specified and implemented by the vendors offers no way to
> discover the printed length of a non-character value.  FreeTDS extends
> dbwillconvert() to do that: instead of a simple boolean, it returns the
> number of bytes needed for a character representation.  I'm sorry it's not
> better documented.  :-(
>
>   
No problem at all, I was just confused by the documentation that I had 
found later. 
> > However, in the Objective C/GUI version it appears to return a Bool.  It
> >
> > seems to return 1 if it is convertable and 0 if it is not.  This 
> > obviously messes up the rest of the allocations in the sample resulting 
> > in truncation and overflow errors.  
> >     
>
> My first instinct was to wonder if in fact you're linking to FreeTDS and
> not one of the vendor libraries, or perhaps to a version prior to 0.82.  I
> assume none of those is the case.  
>
>   
I am linking to a compiled framework however it is the same framework 
for both the C and the Obj-C version. 

> My second guess is to wonder if Objective C is looking at the header file
> (or something like that), interpreting each nonzero return code as "true",
> and returning only 0 or 1.  Is there glue code that allows Objective C to
> call a C library?  Is there some preprocessing that gets done to make C
> functions available to it?  
>
>   
This is probably what is happening as it makes the most sense.  No glue 
code is needed.  Obj-C can directly call all C programs and all C code 
is valid Obj-C code.  But what you said about Obj-C interpreting any non 
zero value as true makes the most sense to me.  What I wonder then is 
there something I can do to make this work without having to change the 
FreeTDS headers (because I would assue a type change would be a 
recompile and change to the actual library?  I am relatively new to C 
and ObjC, so I'm not too experienced in this department. 
> > I then looked into this farther and 
> > found http://www.freetds.org/reference/a00275.html#ga24 which from what 
> > I can tell is that the desired effect of that function is to return the 
> > bool. 
> >     
>
> Ouch.  Yes.  I'll update that.  Thanks for pointing it out.  
>   
No problem, glad I could help, and thanks for the feedback :)

Joe