Re: [Boost-users] [Container] --begin() on empty deque crashes

2013/1/20 Marshall Clow

On Jan 19, 2013, at 8:23 PM, TONGARI wrote:

2013/1/20 Ion Gaztañaga

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El 19/01/2013 13:06, TONGARI escribió:

Hi there,

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The code below would simply crash on g++ 4.7.1/MinGW with default optimization level, it doesn't shown with -O/1/2/3 ------------------------------**---------- boost::container::deque<int> d; --d.begin(); ------------------------------**----------

The problem is that decrementing a begin iterator is not a valid operator, since it would point out of the container.

But wouldn't it be a valid operation as long as we don't dereference from it?

I don't believe so. If it was a pointer, then yes.

The closest I could find in the standard was section 24.2.6 (talking about bidirectional iterators), it says that a precondition for --r is: there exists s such that r == ++s

OK, thanks. According to the requirement it's invalid indeed, I thought that we have ++end() a valid op so it must apply to --begin() as well, but that's not true.