front_insert_iterator


class template
<iterator> 
template <class Container> class front_insert_iterator;

Front insert iterator

Front insert iterators are a special output iterator class designed to allow algorithms that usually overwrite elements (such as copy) to instead insert new elements at the front of the container.

The container must have member push_front defined (such as standard containers deque and list).

Using the assignment operator on the front_insert_iterator, even when dereferenced, causes the container to insert a new element at its beginning. The other typical operators of an output iterator are also defined for front_insert_iterator but have no effect.

It is defined with an identical operation to:
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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; }
};


The library provides a function, called front_inserter, that automatically generates a front_insert_iterator class from a container.

Member functions

constructor
front_insert_iterator objects are constructed from a container.
operator=
Inserts a new element in the container, initializing its value to a copy of 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>
#include <iterator>
#include <deque>
using namespace std;

int main () {
  deque<int> firstdeque, seconddeque;
  for (int i=1; i<=5; i++)
  { firstdeque.push_back(i); seconddeque.push_back(i*10); }

  front_insert_iterator< deque<int> > front_it (firstdeque);

  copy (seconddeque.begin(),seconddeque.end(),front_it);

  deque<int>::iterator it;
  for ( it = firstdeque.begin(); it!= firstdeque.end(); ++it )
	  cout << *it << " ";
  cout << endl;

  return 0;
}


Output:

50 40 30 20 10 1 2 3 4 5


See also

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