[insert.iterators]

# 24 Iterators library [[iterators]](./#iterators)

## 24.5 Iterator adaptors [[predef.iterators]](predef.iterators#insert.iterators)

### 24.5.2 Insert iterators [insert.iterators]

#### [24.5.2.1](#general) General [[insert.iterators.general]](insert.iterators.general)

[1](#general-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L3779)

To make it possible to deal with insertion in the same way as writing into an array, a special kind of iterator
adaptors, called[*insert iterators*](#def:insert_iterators),
are provided in the library[.](#general-1.sentence-1)

With regular iterator classes,while (first != last) *result++ = *first++; causes a range [first, last)
to be copied into a range starting with result[.](#general-1.sentence-2)

The same code withresult being an insert iterator will insert corresponding elements into the container[.](#general-1.sentence-3)

This device allows all of the
copying algorithms in the library to work in the[*insert mode*](#def:insert_mode) instead of the [*regular overwrite*](#def:regular_overwrite) mode[.](#general-1.sentence-4)

[2](#general-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L3798)

An insert iterator is constructed from a container and possibly one of its iterators pointing to where
insertion takes place if it is neither at the beginning nor at the end of the container[.](#general-2.sentence-1)

Insert iterators meet the requirements of output iterators[.](#general-2.sentence-2)

operator* returns the insert iterator itself[.](#general-2.sentence-3)

The assignmentoperator=(const T& x) is defined on insert iterators to allow writing into them, it insertsx right before where the insert iterator is pointing[.](#general-2.sentence-4)

In other words, an insert iterator is like a cursor pointing into the
container where the insertion takes place[.](#general-2.sentence-5)

back_insert_iterator inserts elements at the end of a container,front_insert_iterator inserts elements at the beginning of a container, andinsert_iterator inserts elements where the iterator points to in a container[.](#general-2.sentence-6)

back_inserter,front_inserter,
andinserter are three
functions making the insert iterators out of a container[.](#general-2.sentence-7)

#### [24.5.2.2](#back.insert.iterator) Class template back_insert_iterator [[back.insert.iterator]](back.insert.iterator)

#### [24.5.2.2.1](#back.insert.iter.general) General [[back.insert.iter.general]](back.insert.iter.general)

[🔗](#lib:back_insert_iterator)

namespace std {template<class Container>class back_insert_iterator {protected: Container* container; public:using iterator_category = output_iterator_tag; using value_type = void; using difference_type = ptrdiff_t; using pointer = void; using reference = void; using container_type = Container; constexpr explicit back_insert_iterator(Container& x); constexpr back_insert_iterator& operator=(const typename Container::value_type& value); constexpr back_insert_iterator& operator=(typename Container::value_type&& value); constexpr back_insert_iterator& operator*(); constexpr back_insert_iterator& operator++(); constexpr back_insert_iterator operator++(int); };}

#### [24.5.2.2.2](#back.insert.iter.ops) Operations [[back.insert.iter.ops]](back.insert.iter.ops)

[🔗](#lib:back_insert_iterator,constructor)

`constexpr explicit back_insert_iterator(Container& x);
`

[1](#back.insert.iter.ops-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L3863)

*Effects*: Initializescontainer with addressof(x)[.](#back.insert.iter.ops-1.sentence-1)

[🔗](#lib:operator=,back_insert_iterator)

`constexpr back_insert_iterator& operator=(const typename Container::value_type& value);
`

[2](#back.insert.iter.ops-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L3876)

*Effects*: As if by: container->push_back(value);

[3](#back.insert.iter.ops-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L3880)

*Returns*: *this[.](#back.insert.iter.ops-3.sentence-1)

[🔗](#lib:operator=,back_insert_iterator_)

`constexpr back_insert_iterator& operator=(typename Container::value_type&& value);
`

[4](#back.insert.iter.ops-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L3891)

*Effects*: As if by: container->push_back(std​::​move(value));

[5](#back.insert.iter.ops-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L3895)

*Returns*: *this[.](#back.insert.iter.ops-5.sentence-1)

[🔗](#lib:operator*,back_insert_iterator)

`constexpr back_insert_iterator& operator*();
`

[6](#back.insert.iter.ops-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L3906)

*Returns*: *this[.](#back.insert.iter.ops-6.sentence-1)

[🔗](#lib:operator++,back_insert_iterator)

`constexpr back_insert_iterator& operator++();
constexpr back_insert_iterator  operator++(int);
`

[7](#back.insert.iter.ops-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L3918)

*Returns*: *this[.](#back.insert.iter.ops-7.sentence-1)

#### [24.5.2.2.3](#back.inserter) back_inserter [[back.inserter]](back.inserter)

[🔗](#lib:back_inserter)

`template<class Container>
  constexpr back_insert_iterator<Container> back_inserter(Container& x);
`

[1](#back.inserter-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L3932)

*Returns*: back_insert_iterator<Container>(x)[.](#back.inserter-1.sentence-1)

#### [24.5.2.3](#front.insert.iterator) Class template front_insert_iterator [[front.insert.iterator]](front.insert.iterator)

#### [24.5.2.3.1](#front.insert.iter.general) General [[front.insert.iter.general]](front.insert.iter.general)

[🔗](#lib:front_insert_iterator)

namespace std {template<class Container>class front_insert_iterator {protected: Container* container; public:using iterator_category = output_iterator_tag; using value_type = void; using difference_type = ptrdiff_t; using pointer = void; using reference = void; using container_type = Container; constexpr explicit front_insert_iterator(Container& x); constexpr front_insert_iterator& operator=(const typename Container::value_type& value); constexpr front_insert_iterator& operator=(typename Container::value_type&& value); constexpr front_insert_iterator& operator*(); constexpr front_insert_iterator& operator++(); constexpr front_insert_iterator operator++(int); };}

#### [24.5.2.3.2](#front.insert.iter.ops) Operations [[front.insert.iter.ops]](front.insert.iter.ops)

[🔗](#lib:front_insert_iterator,constructor)

`constexpr explicit front_insert_iterator(Container& x);
`

[1](#front.insert.iter.ops-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L3976)

*Effects*: Initializescontainer with addressof(x)[.](#front.insert.iter.ops-1.sentence-1)

[🔗](#lib:operator=,front_insert_iterator)

`constexpr front_insert_iterator& operator=(const typename Container::value_type& value);
`

[2](#front.insert.iter.ops-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L3989)

*Effects*: As if by: container->push_front(value);

[3](#front.insert.iter.ops-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L3993)

*Returns*: *this[.](#front.insert.iter.ops-3.sentence-1)

[🔗](#lib:operator=,front_insert_iterator_)

`constexpr front_insert_iterator& operator=(typename Container::value_type&& value);
`

[4](#front.insert.iter.ops-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L4004)

*Effects*: As if by: container->push_front(std​::​move(value));

[5](#front.insert.iter.ops-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L4008)

*Returns*: *this[.](#front.insert.iter.ops-5.sentence-1)

[🔗](#lib:operator*,front_insert_iterator)

`constexpr front_insert_iterator& operator*();
`

[6](#front.insert.iter.ops-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L4019)

*Returns*: *this[.](#front.insert.iter.ops-6.sentence-1)

[🔗](#lib:operator++,front_insert_iterator)

`constexpr front_insert_iterator& operator++();
constexpr front_insert_iterator  operator++(int);
`

[7](#front.insert.iter.ops-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L4031)

*Returns*: *this[.](#front.insert.iter.ops-7.sentence-1)

#### [24.5.2.3.3](#front.inserter) front_inserter [[front.inserter]](front.inserter)

[🔗](#lib:front_inserter)

`template<class Container>
  constexpr front_insert_iterator<Container> front_inserter(Container& x);
`

[1](#front.inserter-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L4045)

*Returns*: front_insert_iterator<Container>(x)[.](#front.inserter-1.sentence-1)

#### [24.5.2.4](#insert.iterator) Class template insert_iterator [[insert.iterator]](insert.iterator)

#### [24.5.2.4.1](#insert.iter.general) General [[insert.iter.general]](insert.iter.general)

[🔗](#lib:insert_iterator)

namespace std {template<class Container>class insert_iterator {protected: Container* container;
 ranges::iterator_t<Container> iter; public:using iterator_category = output_iterator_tag; using value_type = void; using difference_type = ptrdiff_t; using pointer = void; using reference = void; using container_type = Container; constexpr insert_iterator(Container& x, ranges::iterator_t<Container> i); constexpr insert_iterator& operator=(const typename Container::value_type& value); constexpr insert_iterator& operator=(typename Container::value_type&& value); constexpr insert_iterator& operator*(); constexpr insert_iterator& operator++(); constexpr insert_iterator& operator++(int); };}

#### [24.5.2.4.2](#insert.iter.ops) Operations [[insert.iter.ops]](insert.iter.ops)

[🔗](#lib:insert_iterator,constructor)

`constexpr insert_iterator(Container& x, ranges::iterator_t<Container> i);
`

[1](#insert.iter.ops-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L4090)

*Effects*: Initializescontainer with addressof(x) anditer with i[.](#insert.iter.ops-1.sentence-1)

[🔗](#lib:operator=,insert_iterator)

`constexpr insert_iterator& operator=(const typename Container::value_type& value);
`

[2](#insert.iter.ops-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L4105)

*Effects*: As if by:iter = container->insert(iter, value);++iter;

[3](#insert.iter.ops-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L4113)

*Returns*: *this[.](#insert.iter.ops-3.sentence-1)

[🔗](#lib:operator=,insert_iterator_)

`constexpr insert_iterator& operator=(typename Container::value_type&& value);
`

[4](#insert.iter.ops-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L4124)

*Effects*: As if by:iter = container->insert(iter, std::move(value));++iter;

[5](#insert.iter.ops-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L4132)

*Returns*: *this[.](#insert.iter.ops-5.sentence-1)

[🔗](#lib:operator*,insert_iterator)

`constexpr insert_iterator& operator*();
`

[6](#insert.iter.ops-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L4143)

*Returns*: *this[.](#insert.iter.ops-6.sentence-1)

[🔗](#lib:operator++,insert_iterator)

`constexpr insert_iterator& operator++();
constexpr insert_iterator& operator++(int);
`

[7](#insert.iter.ops-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L4155)

*Returns*: *this[.](#insert.iter.ops-7.sentence-1)

#### [24.5.2.4.3](#inserter) inserter [[inserter]](inserter)

[🔗](#lib:inserter)

`template<class Container>
  constexpr insert_iterator<Container>
    inserter(Container& x, ranges::iterator_t<Container> i);
`

[1](#inserter-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L4170)

*Returns*: insert_iterator<Container>(x, i)[.](#inserter-1.sentence-1)