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Reference

class template
<iterator>

std::front_insert_iterator

template <class Container> class front_insert_iterator;
Front insert iterator

Front-insert iterators are specialoutput iterators designed to allowalgorithms that usually overwrite elements (such ascopy) to instead insert new elements at the beginning of the container.

The container needs to have apush_front member function (such as the standard containersdeque andlist).

Using the assignment operator on thefront_insert_iterator (both while being dereferenced or not), causes the container to expand by one element, which is initialized to the value assigned.

The other typical operators of anoutput iterator are also defined forfront_insert_iterator but have no effect: all values assigned are inserted at the beginning of the container.

It is defined with the same behavior as:
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template <class Container>class front_insert_iterator :public iterator<output_iterator_tag,void,void,void,void>{protected:  Container* container;public:typedef Container container_type;explicit front_insert_iterator (Container& x) : container(&x) {}  front_insert_iterator<Container>&operator= (typename Container::const_reference value)    { container->push_front(value);return *this; }  front_insert_iterator<Container>&operator* ()    {return *this; }  front_insert_iterator<Container>&operator++ ()    {return *this; }  front_insert_iterator<Container>operator++ (int)    {return *this; }};
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template <class Container>class front_insert_iterator :public iterator<output_iterator_tag,void,void,void,void>{protected:  Container* container;public:typedef Container container_type;explicit front_insert_iterator (Container& x) : container(&x) {}  front_insert_iterator<Container>&operator= (consttypename Container::value_type& value)    { container->push_front(value);return *this; }  front_insert_iterator<Container>&operator= (typename Container::value_type&& value)    { container->push_front(std::move(value));return *this; }  front_insert_iterator<Container>&operator* ()    {return *this; }  front_insert_iterator<Container>&operator++ ()    {return *this; }  front_insert_iterator<Container>operator++ (int)    {return *this; }};
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template <class Container>class front_insert_iterator :public iterator<output_iterator_tag,void,void,void,void>{protected:  Container* container;public:typedef Container container_type;explicit front_insert_iterator (Container& x) : container(std::addressof(x)) {}  front_insert_iterator<Container>&operator= (consttypename Container::value_type& value)    { container->push_front(value);return *this; }  front_insert_iterator<Container>&operator= (typename Container::value_type&& value)    { container->push_front(std::move(value));return *this; }  front_insert_iterator<Container>&operator* ()    {return *this; }  front_insert_iterator<Container>&operator++ ()    {return *this; }  front_insert_iterator<Container>operator++ (int)    {return *this; }};

The library provides a function, calledfront_inserter, that automatically generates afront_insert_iterator class from a suitable container.

Template parameters

Container
A container class with memberpush_front defined (such as the standard containersdeque andlist).

Member types

memberdefinition infront_insert_iterator
iterator_categoryoutput_iterator_tag
value_typevoid
difference_typevoid
pointervoid
referencevoid
iterator_typevoid

Member functions

constructor
front_insert_iterator objects are constructed from a container, of which they keep a reference internally.
operator=
Inserts a new element at the beginning of the container, initializing it with the argument.
operator*
Does nothing. Returns a reference to the object.
operator++
Does nothing. Returns a reference to the object.

Example

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// front_insert_iterator example#include <iostream>// std::cout#include <iterator>// std::front_insert_iterator#include <deque>// std::deque#include <algorithm>// std::copyint main () {  std::deque<int> foo, bar;for (int i=1; i<=5; i++)  { foo.push_back(i); bar.push_back(i*10); }  std::front_insert_iterator< std::deque<int> > front_it (foo);  std::copy (bar.begin(),bar.end(),front_it);  std::cout <<"foo:";for ( std::deque<int>::iterator it = foo.begin(); it!= foo.end(); ++it )  std::cout <<' ' << *it;  std::cout <<'\n';return 0;}

Output:
50 40 30 20 10 1 2 3 4 5


See also

front_inserter
Constructs front insert iterator(function template)
back_insert_iterator
Back insert iterator(class template)
insert_iterator
Insert iterator(class template)
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