# std::front_insert_iterator

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< cpp‎ | 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 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)

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