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Are standard container iterators DefaultConstructible?

Is it well formed?

int main() {
    std::deque< int >::iterator x; // Or any container.
}

Bonus questions:

  • What about a auto y = x;potential copy of an uninitialized state?
  • What about … x = {};, which requires an implicit default constructor?
  • What about x == yif both are initialized with a value (not initialized by default, as shown)?
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2 answers

Depends on the Iterator concept you are testing.

Iterator, , , , CopyConstructible, CopyAssignable Destructible. (§ 24.2.2/2)

( std::forward_list, ). ForwardIterator, InputIterator ( ).

ForwardIterator :

X ,

- X (24.2.3),

- X DefaultConstructible (17.6.3.1),

§ 24.2.5/1 N3376

, .

§ 24.2, cppreference

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, , , .

§24.2.2 [iterator.iterators] (n3485), Iterator () DefaultConstructible. , §24.2.3 [input.iterators] $24.2.4 [output.iterators], InputIterator OutputIterator.

§24.2.5 [forward.iterators], :

1/ X ,

  • X (24.2.3),
  • X DefaultConstructible (17.6.3.1) [...]

, ForwardIterator, .

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