Re: CoW and reference counting in the STL

From:

=?ISO-8859-1?Q?Daniel_Kr=FCgler?= <daniel.kruegler@googlemail.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Wed, 14 Apr 2010 17:38:39 CST

Message-ID:

<20827530-3772-4d97-86ce-d3fac10c8ce3@q23g2000yqd.googlegroups.com>

On 14 Apr., 20:44, s5n <sgb...@googlemail.com> wrote:

My question might be slightly off-topic, as it is specific to the STL
(and in fact specific to implementation-defined features), but this is
the best place i know to ask...

The question is not off-topic at all.

std::string typically uses reference counting and CoW to reduce real
allocations to a minimum. i understand that this is an implementation-
defined detail, not standardized, but in my experience STL
implementations do this.

Yes, this is a valid implementation technique for C++03,
but no longer valid for C++0x. Todays implementations often
take advantage of the small-string optimization, though.

What i don't know is: do STL implementations
also (typically) do the same for std::vector?

No, that would contradict the specification. If such
implementation were intended to be supported, much more
member functions of std::vector would need to allow for
invalidation of pointers, iterators, and references,
e.g the non-const overloads of at, operator[], etc.

HTH & Greetings from Bremen,

Daniel Kr?gler

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