Re: [xml] vsnprintf

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:

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.


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

Andrew W. Nosenko <andrew w nosenko gmail com>

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