Re: strange crash after assertion with std::map::iterator

From:

"Doug Harrison [MVP]" <dsh@mvps.org>

Newsgroups:

microsoft.public.vc.stl

Date:

Mon, 16 Apr 2007 10:47:49 -0500

Message-ID:

<hq5723d6bt2b41tna5iu821cca9t3ph02c@4ax.com>

On Mon, 16 Apr 2007 14:40:21 +0200, "Mycroft Holmes" <m.holmes@nospam.it>
wrote:

Hi,

I thought the following code was legal:

std::map<int, int>::iterator i, j;
bool t = (i == j);

instead I'm getting an assertion from STL. Also, after the expression the
program crashes (i.e. it's unable to continue debugging).
1) is the assertion correct? iterators are supposed to be default
constructable; such a default iterator should not be used, but I assume "to
use" means increment, decrement or dereference...
2) has anyone experienced the same crash?

Container iterators only make sense relative to the container from which
they are initialized. If they haven't been initialized from an iterator
obtained from a container operation such as begin(), end(), some forms of
insert(), etc, or they have been invalidated subsequent to some container
operation, then you can't compare them or do anything except assign them a
good iterator value. You may be thinking of an input iterator, such as
istream_iterator, whose default constructor creates the "end" value for
that type of iterator. Unless the documentation for an iterator states its
default ctor creates a valid iterator, you should assume that it does not.

--
Doug Harrison
Visual C++ MVP