Assertion when using const_iterator

Question

I'm testing the use of an interface which has the function foo. Here is my implementation of this function in my mock:

class Mock
{
public:
    void foo(Foo::const_iterator begin, Foo::const_iterator end) {
      _begin = begin;
      _end = end;

      ...
    }
    ...
    Foo::const_iterator _begin;
    Foo::const_iterator _end;
};

I then have a test which checks if foo has been called:

// test that function foo is not called
EXPECT_EQ(mock->_begin, Foo::const_iterator());

But this is giving me an assertion in Visual Studio claiming that the iterators are incompatible. I would have expected that _begin would be equal to Foo::const_iterator() if I havent called foo(). Why isn't it?

Does `operator ==` of `Foo::const_iterator()` allow comparing two default-constructed instances against each other? Making the default-constructed iterator be "invalid" and "different from any iterator" would be a valid choice of semantics. — Angew is no longer proud of SO, Apr 12 '13 at 14:42

score 1 · Answer 1 · answered Apr 12 '13 at 14:58

1

Iterators are only comparable if they're pointing to the same container. A default-constructed iterator isn't pointing to a container at all, so it's not compatible with anything by definition.

answered Apr 12 '13 at 14:58

Mark Ransom

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Yep, that sums it up. Such iterators have a so-called "singular value", which is the search term that will explain this. – Ulrich Eckhardt Apr 12 '13 at 17:43

Mark B · Answer 2 · 2013-04-12T14:58:53.327

0

Perhaps VS implements their iterator compatibility checks with default constructed iterators treated in such a way that a default constructed iterator is never compatible with any other iterator, even a default constructed one.

edited Apr 12 '13 at 14:58

answered Apr 12 '13 at 14:50

Mark B

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Assertion when using const_iterator

2 Answers2