Re: reclaiming memory guarantees

From:

=?UTF-8?B?RXJpayBXaWtzdHLDtm0=?= <Erik-wikstrom@telia.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Sun, 1 Jun 2008 18:28:51 CST

Message-ID:

<QUs0k.7842$R_4.6536@newsb.telia.net>

On 2008-06-01 11:00, iy@mailinator.com wrote:

{ Please don't top-post. -mod }

Thank you, that's what I suspected. So we only have this 'in practice' guarantee,
which any STL implementation free to deviate from.

However, do you know if this guarantee holds for associative containers?
That is, we know, in practice, that the swap trick should trim the memory
of a vector, in a non-eccentric STL implementation, but would it trim the
excessive memory of a map (if the map pre-allocates memory, for example)?

IMO it would be fair to assume that if the STL implementation bothers to
pre-allocate memory in map implementation, they would trim it when the swap
trick is applied.

While I have not checked I doubt that any implementation pre-allocates
for any container except vector (and perhaps dequeu, can't remember how
it works) since the benefit of doing so is quite small since no re-
allocation is need of already existing elements when new ones are
inserted. This would also mean that the memory freed by removing one
element will probably directly be available for new allocations.

--
Erik Wikstr??m

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