Re: [xml] vsnprintf

["Andrew W. Nosenko" <andrew w nosenko gmail com>]

On Thu, Dec 16, 2010 at 15:42, Adrian Bunk <bunk stusta de> wrote:
> On Wed, Dec 15, 2010 at 12:46:00PM -0600, Peter O'Gorman wrote:
> > Hi,
> >
> > We saw some test failures running the python tests for libxml-2.7.8 that
> > turned out to be related to libc's vsnprintf being buggy.
> >
> > Unfortunately, though vsnprintf(buf,len,format,ap) should return the number
> > of chars that would have been written to buf (not including the final
> > NULL), not all systems see it that way.
> > ...
>
> It is not that simple, snprintf(3) on Linux says:
>
>       Concerning  the  return  value  of snprintf(), SUSv2 and C99 contradict
>       each other: when snprintf() is called with size=0 then SUSv2 stipulates
>       an  unspecified  return  value  less than 1, while C99 allows str to be
>       NULL in this case, and gives the return value (as always) as the number
>       of  characters  that  would have been written in case the output string
>       has been large enough.

Both SUSv3 and SUSv4 say:
If the value of n is zero on a call to snprintf(), nothing shall be
written, the number of bytes that would have been written had n been
sufficiently large excluding the terminating null shall be returned,
and s may be a null pointer.

SUSv3: http://pubs.opengroup.org/onlinepubs/009695399/functions/snprintf.html
SUSv4: http://pubs.opengroup.org/onlinepubs/9699919799/functions/snprintf.html

Thus, at least, we know to where the world is moving :-)

-- 
Andrew W. Nosenko <andrew w nosenko gmail com>