Re: [Boost-bugs] [Boost C++ Libraries] #11609: circular_buffer erroneously invalidates reverse_iterator at pop_back in debug mode

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #11609: circular_buffer erroneously invalidates reverse_iterator at pop_back in debug mode
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2015-09-02 17:54:42

#11609: circular_buffer erroneously invalidates reverse_iterator at pop_back in
debug mode
-----------------------------------+-----------------------------
  Reporter:  christian.stimming@…  |      Owner:  jano_gaspar
      Type:  Bugs                  |     Status:  new
 Milestone:  To Be Determined      |  Component:  circular_buffer
   Version:  Boost 1.57.0          |   Severity:  Problem
Resolution:                        |   Keywords:
-----------------------------------+-----------------------------
Changes (by viboes):

 * owner:   => jano_gaspar
 * component:  None => circular_buffer


Old description:

> The circular_buffer container offers reverse iterators. Using one so that
> it points to the second-to-last element would in theory allow to
> pop_back() the last element without causing problems with that iterator.
> However, apparently pop_back() invalidates those reverse iterators even
> though they wouldn't cause problems, as if the debug_iterator_registry in
> boost/circular_buffer/debug.hpp is working correctly only for forward
> iterators but not for backward iterators.
>
> Example code that works fine without debug mode, but will run into a
> failed assertion in debug mode:
>
> #define BOOST_CB_ENABLE_DEBUG
> #include <boost/circular_buffer.hpp>
> #include <iostream>
> int main(int /*argc*/, char** /*argv*/) {
>         typedef boost::circular_buffer<int> CircBuffer;
>         CircBuffer testBuffer(2);
>         testBuffer.push_back(4);
>         testBuffer.push_back(8);
>
>         CircBuffer::const_reverse_iterator bufIter = testBuffer.rbegin();
>         std::cout << "element at rbegin=" << *bufIter << std::endl; //
> prints "=8" correctly
>         ++bufIter;
>         std::cout << "element after ++=" << *bufIter << std::endl; //
> prints "=4" correctly
>         testBuffer.pop_back();
>         std::cout << "elem=" << *bufIter << std::endl; // ERROR: Causes
> "Assertion `is_valid(m_buff)' failed."
> }

New description:

 The circular_buffer container offers reverse iterators. Using one so that
 it points to the second-to-last element would in theory allow to
 pop_back() the last element without causing problems with that iterator.
 However, apparently pop_back() invalidates those reverse iterators even
 though they wouldn't cause problems, as if the debug_iterator_registry in
 boost/circular_buffer/debug.hpp is working correctly only for forward
 iterators but not for backward iterators.

 Example code that works fine without debug mode, but will run into a
 failed assertion in debug mode:


 {{{
 #define BOOST_CB_ENABLE_DEBUG
 #include <boost/circular_buffer.hpp>
 #include <iostream>
 int main(int /*argc*/, char** /*argv*/) {
         typedef boost::circular_buffer<int> CircBuffer;
         CircBuffer testBuffer(2);
         testBuffer.push_back(4);
         testBuffer.push_back(8);

         CircBuffer::const_reverse_iterator bufIter = testBuffer.rbegin();
         std::cout << "element at rbegin=" << *bufIter << std::endl; //
 prints "=8" correctly
         ++bufIter;
         std::cout << "element after ++=" << *bufIter << std::endl; //
 prints "=4" correctly
         testBuffer.pop_back();
         std::cout << "elem=" << *bufIter << std::endl; // ERROR: Causes
 "Assertion `is_valid(m_buff)' failed."
 }
 }}}

--
-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/11609#comment:2>
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