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Re: snprintf(3) behaviour regarding large "n"
On Wed, Oct 01, 2014 at 01:06:46PM +0200, Steffen Nurpmeso wrote:
> David Holland <dholland-tech%netbsd.org@localhost> wrote:
> |On Mon, Sep 29, 2014 at 09:49:18PM +0200, Steffen Nurpmeso wrote:
> |> I just looked at OpenBSD now -- they clamp to INT_MAX if >INT_MAX,
> |> which is a much more sane approach that i would also have
> |Problem with that is that there's a lot of code that checks if the
> |return value is less than the max size to see if the string (didn't)
> |get truncated. So if you clamp the max size, this logic breaks.
> Does the function stop processing and return EOVERFLOW if the
> result would exceed that "int" that is used for the return value,
> i.e. the actual buffer size?
> If so, i think you are creating an artificial problem.
It does not:
snprintf(), vsnprintf(), and vsnprintf_ss() will write at most size-1 of
the characters printed into the output string (the size'th character then
gets the terminating `\0'); if the return value is greater than or equal
to the size argument, the string was too short and some of the printed
characters were discarded.
> P.S.: this snippet flew by when i (git) grep'ed in usr.bin for
> snprintf(3) usage (gzip/gzip.c) and isn't multibyte safe.
> Shall i open a bug report?
> /* Add (usually) .gz to filename */
> if ((size_t)snprintf(outfile, outsize, "%s%s",
> file, suffixes.zipped) >= outsize)
> memcpy(outfile + outsize - suffixes.ziplen - 1,
> suffixes.zipped, suffixes.ziplen + 1);
Other than it should check for error in case of EILSEQ, that's more or
less the normal idiom...
David A. Holland
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