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std::front_insert_iterator

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 a LegacyOutputIterator 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
iterator_category std::output_iterator_tag
value_type void
difference_type

void

 (until C++20)

std::ptrdiff_t

 (since C++20)
pointer void
reference void
container_type Container

Member types iterator_category, value_type, difference_type, pointer and reference are required to be obtained by inheriting from std::iterator<std::output_iterator_tag, void, void, void, void>.

 (until C++17)

Member functions

constructs a new front_insert_iterator
(public member function)
inserts an object into the associated container
(public member function)
no-op
(public member function)
no-op
(public member function)

Member objects

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

Example

#include <algorithm>
#include <deque>
#include <iostream>
#include <iterator>
#include <vector>
 
namespace stb
{
    void println(auto, auto const& d)
    {
        std::ranges::copy(d, std::ostream_iterator<int>(std::cout, " "));
        std::cout << '\n';
    }
}
 
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)
 
    stb::println("{}", d);
}

Output:

5 4 3 2 1

See also

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

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