On Thursday, 16 April 2026 02:00:53 Pacific Daylight Time Marcin Jaczewski via
Std-Proposals wrote:
> This means the standard should guarantee that we can't allocate more
> than `MAX_INT` and I recall that C had something like this as
> there was a macro that was "max allocation size".
> With this most rollovers will not be a problem.

malloc() cannot return a block bigger than PTRDIFF_MAX-1, because then the
distance between one-past-end and the beginning would be negative. You may
have seen the annoying warnings from GCC that you may be trying to allocate
more than 2^63 bytes (even though you aren't).

On some esoteric platform where ptrdiff_t is bigger than size_t, SIZE_MAX would
be the limit. On almost everything, they have the same size, so PTRDIFF_MAX is
the limit.

That means there are exactly two containers in the Standard that could have
more than PTRDIFF_MAX elements, on a common (albeit 32-bit these days)
platform: std::deque<char> and std::bitset.

> I read that a long time ago about this and possibly I confuse
> something, but after googling I found this:
> `RSIZE_MAX` but it's not linked directly to `malloc` more for safer C
> string functions.

Yeah, that's Annex K stuff. Forget it exists.

-- 
Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
  Principal Engineer - Intel Data Center - Platform & Sys. Eng.