# std::back_insert_iterator

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< cpp‎ | iterator

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

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

### Member types

Member type | Definition
`container_type` | `Container`

### Member functions

(constructor) | constructs a new `back_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 <iostream>
    #include <iterator>
    #include <algorithm>
    #include <cstdlib>
    #include <vector>

    int main()
    {
        std::vector<int> v;
        std::generate_n(std::back_insert_iterator<std::vector<int>>(v), // can be simplified
                        10, [](){ return std::rand() % 10; });        // with std::back_inserter
        for (int n : v)
            std::cout << n << ' ';
        std::cout << '\n';
    }

Output:

    3 6 7 5 3 5 6 2 9 1

### See also

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

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