std::front_insert_iterator

 

C++

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Technical Specifications

 

Iterator library

Iterator primitives
iterator_traits
input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tag
iterator
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reverse_iterator move_iterator (C++11) back_insert_iterator front_insert_iterator insert_iterator	make_reverse_iterator (C++14) make_move_iterator (C++11) back_inserter front_inserter inserter
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size (C++17)
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data (C++17)

 

std::front_insert_iterator

Member functions

front_insert_iterator::front_insert_iterator

front_insert_iterator::operator=

front_insert_iterator::operator*

front_insert_iterator::operator++front_insert_iterator::operator++(int)

 

Defined in header <iterator>
template< class Container > class front_insert_iterator : public std::iterator< std::output_iterator_tag,                                                    void,void,void,void >		(until C++17)
template< class Container > class front_insert_iterator;		(since C++17)

std::front_insert_iterator is an OutputIterator that prepends elements to a container for which it was constructed. The container's push_front() member function is called whenever the iterator (whether dereferenced or not) is assigned to. Incrementing the std::front_insert_iterator is a no-op.

Member types

Member type	Definition
container_type	Container

Member functions

(constructor)	constructs a new front_insert_iterator (public member function)
operator=	inserts an object into the associated container (public member function)
operator*	no-op (public member function)
operator++operator++(int)	no-op (public member function)

Member objects

Member name	Definition
container (protected)	a pointer of type Container*

Member types

Member type	Definition
value_type	void
difference_type	void
pointer	void
reference	void
iterator_category	std::output_iterator_tag

Note: before C++17, these member types are required to be obtained by inheriting from std::iterator<std::output_iterator_tag,void,void,void,void>.

Example

Run this code

#include <vector>
#include <deque>
#include <iostream>
#include <iterator>
#include <algorithm>
int main()
{
    std::vector<int> v{1,2,3,4,5};
    std::deque<int> d;
    std::copy(v.begin(), v.end(),
              std::front_insert_iterator<std::deque<int>>(d)); // or std::front_inserter(d)
    for(int n : d)
        std::cout << n << ' ';
    std::cout << '\n';
}

Output:

5 4 3 2 1

See also

front_inserter	creates a std::front_insert_iterator of type inferred from the argument (function template)
back_insert_iterator	iterator adaptor for insertion at the end of a container (class template)
insert_iterator	iterator adaptor for insertion into a container (class template)