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From: Gabriel Dos Reis <gdr@integrable-solutions.net> To: bkoz@gcc.gnu.org Cc: gcc-prs@gcc.gnu.org, Subject: Re: libstdc++/8230: Buggy allocator behaviour Date: Wed, 20 Nov 2002 18:02:00 -0000 [thread overview] Message-ID: <20021114150601.13602.qmail@sources.redhat.com> (raw) The following reply was made to PR libstdc++/8230; it has been noted by GNATS. From: Gabriel Dos Reis <gdr@integrable-solutions.net> To: bkoz@gcc.gnu.org Cc: gcc-bugs@gcc.gnu.org, jkanze@caicheuvreux.com, gcc-gnats@gcc.gnu.org, libstdc++@gcc.gnu.org Subject: Re: libstdc++/8230: Buggy allocator behaviour Date: 14 Nov 2002 15:59:43 +0100 bkoz@gcc.gnu.org writes: | Synopsis: Buggy allocator behaviour | | Responsible-Changed-From-To: unassigned->bkoz | Responsible-Changed-By: bkoz | Responsible-Changed-When: Wed Nov 13 14:19:11 2002 | Responsible-Changed-Why: | Mine. | State-Changed-From-To: open->feedback | State-Changed-By: bkoz | State-Changed-When: Wed Nov 13 14:19:11 2002 | State-Changed-Why: | I don't think this is an allocator::allocate issue per se. The member function reserve is only in std::vector and std::vector<bool>, and the standard says Hi Benjamin, This issue is a conjugation of both std::allocator<> and std::vector<> ill-behaviour. Fixing std::vector<> fixes a part of the problem (i.e. the testcase provided will pass), but leaves completely unfixed the std::allocator<> bits as required by the standard: 20.4.1.1 allocator members 2/ pointer allocator(size_type n, allocator<void>::const_pointer = 0); 7/ Throws: bad_alloc if the storage cannot be obtained 20.4.1.1/11 size_type max_size() const throw(); returns the largest value N for which the call allocate(N, 0) might succeed. Now consider int main() { try { std::allocator<int> alloc; const std::allocator<int>::size_type n = alloc.max_size(); int* p = alloc.allocate(n + 1); p[n] = 2002; std::cout << p[n] << std::endl; } catch(const std::bad_alloc& e) { std::cerr << e.what() << std::endl; } } This coredumps on my machine using current source. The problem here is that std::allocator<> is not checking the bounds as required and it is lying. On fr.comp.lang.c++, I developed a theory to the effect that std::vector<> may always not check the bounds and still remain conformant *provided* that the allocator is doing the right thing. | 23.2.4.2 - vector capacity | | -4- Throws: length_error if n > max_size().* | | Where allocator::allocate doesn't know what vector::max_size is. Agreed. | | This fix brings the code up to conformance, and is the best fix I think. It, however, does not address the std::allocator<> ill-behaviour. I'm also nervous about: std::vector<int> v; v.resize(v.max_size()); v[v.max_size() - 1] = 2002; I didn't test it with your patch. -- Gaby
next reply other threads:[~2002-11-14 15:06 UTC|newest] Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top 2002-11-20 18:02 Gabriel Dos Reis [this message] -- strict thread matches above, loose matches on Subject: below -- 2002-11-23 1:16 bkoz 2002-11-21 14:01 Richard Henderson 2002-11-21 4:06 Gabriel Dos Reis 2002-11-21 3:47 Matt Austern 2002-11-20 23:03 Gabriel Dos Reis 2002-11-20 19:09 Gabriel Dos Reis 2002-11-20 18:20 Benjamin Kosnik 2002-11-20 18:19 Benjamin Kosnik 2002-11-20 5:07 bkoz 2002-10-15 5:56 gdr
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