Re: UB status of snprintf on invalid ptr+size combination?

[Andreas Schwab <schwab@suse.de>]

On Mär 14 2023, Paul Eggert wrote:

> For example, it's valid for snprintf to be implemented this way:
>
>   int
>   snprintf (char *buf, size_t size, char const *fmt, ...)
>   {
>      char *buf_limit = buf + size;
>      ...
>   }
>
> even though this would have undefined behavior if BUF points to a
> character array smaller than SIZE.

Since it is part of the implementation it is irrelevant from the POV of
the standard.  The implementation does not have to abide to the C
standard, as long as it properly implements the interface constraints.

What matters is the wording of the standard.  The POSIX standard is more
explicit here: "with the addition of the n argument which states the
size of the buffer referred to by s."  Probably the C standard should be
clarified.

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
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