C++ named requirements: LegacyForwardIterator
A LegacyForwardIterator is a LegacyIterator that can read data from the pointed-to element.
Unlike LegacyInputIterator and LegacyOutputIterator, it can be used in multipass algorithms.
If a LegacyForwardIterator it originates from a Container, then it's value_type is the same as the container's, so dereferencing (*it) obtains the container's value_type.
The type It satisfies LegacyForwardIterator if
- The type It satisfies LegacyInputIterator
- The type It satisfies DefaultConstructible
- Objects of the type It provide multipass guarantee described below
- Let T be the value type of It. The type std::iterator_traits<It>::reference must be either
- T& or T&& (since C++11) if It satisfies LegacyOutputIterator (It is mutable), or
- const T& or const T&& (since C++11) otherwise (It is constant),
- (where T is the type denoted by std::iterator_traits<It>::value_type)
- Equality and inequality comparison is defined over all iterators for the same underlying sequence and the value initialized-iterators (since C++14).
- i, dereferenceable lvalue of type It
- reference, the type denoted by std::iterator_traits<It>::reference
The following expressions must be valid and have their specified effects
|Expression||Return type||Equivalent expression|
|i++||It||It ip = i; ++i; return ip;|
A mutable LegacyForwardIterator is a LegacyForwardIterator that additionally satisfies the LegacyOutputIterator requirements.
 Multipass guarantee
Given a and b, dereferenceable iterators of type It
- If a and b compare equal (a == b is contextually convertible to true) then either they are both non-dereferenceable or *a and *b are references bound to the same object.
- If *a and *b refer to the same object, then a == b.
- Assignment through a mutable
ForwardIteratoriterator cannot invalidate the iterator (implicit due to reference defined as a true reference).
- Incrementing a copy of a does not change the value read from a (formally, either It is a raw pointer type or the expression (void)++It(a), *a is equivalent to the expression *a).
- a == b implies ++a == ++b.
Singular iteratorsA value-initialized LegacyForwardIterator behaves like the past-the-end iterator of some unspecified empty container: it compares equal to all value-initialized LegacyForwardIterators of the same type.
For the definition of std::iterator_traits, the following exposition-only concept is defined.
where the exposition-only concept
 Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
|DR||Applied to||Behavior as published||Correct behavior|
||also allows rvalue reference|
 See also
| specifies that an |
|Iterator library||provides definitions for iterators, iterator traits, adaptors, and utility functions|