std::deque::swap invalidates begin() and end() iterators on empty container

• Key: STDCXX-635
• Type: Bug
• Status: Closed
• Resolution: Fixed
• Priority: Minor
• Assignee: Farid Zaripov
• Reporter: Farid Zaripov
• Component/s: 23. Containers
• Affects Version/s: 4.2.0
• Fix Version/s: 4.2.1

Description

The program below aborts on assert.

#include <deque>
#include <cassert>

int main ()
{
typedef std::deque<int> Deque;
typedef Deque::iterator Iter;

Deque d1, d2;

Iter iters [2][2] = {
{ d1.begin (), d1.end () },

{ d2.begin (), d2.end () }

};

d1.swap (d2);

assert (d2.begin () == iters [0][0]);
assert (d2.end ()== iters [0][1]);
assert (d1.begin () == iters [1][0]);
assert (d1.end ()== iters [1][1]);

return 0;
}

Comments

[Farid Zaripov]

The addition information can be found in this thread: http://www.mail-archive.com/[e-mail]/msg03868.html

[Farid Zaripov]

Personally, I don't think that this is a bug.

After swap operation the d1.begin() == d1.end() and they are valid end iterators for the d1 (d2.begin() == d2.end() and they are valid end iterators for the d2). The only thing that was changed is the binary representation of the iterators, so that operator==(d1.begin() before swap, d2.begin() after swap) returns false.

Just for the information: the Dinkumware STL has the same behavior even on non-empty deque's, because its std::deque::iterator has member deque*_Mycont, so the before swap d1.begin()._Mycont == &d1; after swap d2.begin()._Mycont == &d2; and as a result d1.begin() != d2.begin() in any case.

[Farid Zaripov]

See the discussion: http://www.mail-archive.com/[e-mail]/msg03868.html

Fixed thus: http://svn.apache.org/viewvc?rev=637539&view=rev

The _C_cur data member of the deque iterator equal to 0 if and only if the deque is empty.
So if one of the iterators passed as arguments to operator-() is iterator of the empty deque, we can return the difference between _C_cur members of these iterators. So if both of them are iterators from the same deque - the result == 0 is valid. If these iterators are from different deque's, the result is undefined, but standard says nothing about result of subtracting the iterators of the different containers. Also if both of these iterators are iterators from different empty deque's, the result will be 0, but this result is still meets the standard requirements (0 value is part of undefined values range).

[Farid Zaripov]

Issue will be closed after successfull nightly testing and merging in 4.2.x branch.

[Farid Zaripov]

Merged in 4.2.x branch thus: http://svn.apache.org/viewvc?view=rev&revision=648752