back_insert_iterator Class

Describes an iterator adaptor that satisfies the requirements of an output iterator. It inserts, rather than overwrites, elements into the back end of a sequence and thus provides semantics that are different from the overwrite semantics provided by the iterators of the C++ sequence containers. The back_insert_iterator class is templatized on the type of container.

Syntax

template <class Container>
class back_insert_iterator;

Parameters

Container
The type of container into the back of which elements are to be inserted by a back_insert_iterator.

Remarks

The container must satisfy the requirements for a back insertion sequence where is it possible to insert elements at the end of the sequence in amortized constant time. C++ Standard Library sequence containers defined by the deque Class, list Class and vector Class provide the needed push_back member function and satisfy these requirements. These three containers and strings may each be adapted to use with back_insert_iterators. A back_insert_iterator must always be initialized with its container.

Constructors

Constructor	Description
back_insert_iterator	Constructs a back_insert_iterator that inserts elements after the last element in a container.

Typedefs

Type name	Description
container_type	A type that provides a container for the back_insert_iterator.
reference	A type that provides a reference for the back_insert_iterator.

Operators

Operator	Description
operator*	Dereferencing operator used to implement the output iterator expression * i = x for a back insertion.
operator++	Increments the back_insert_iterator to the next location into which a value may be stored.
operator=	Assignment operator used to implement the output iterator expression * i = x for a back insertion.

Requirements

Header: <iterator>

Namespace: std

back_insert_iterator::back_insert_iterator

Constructs a back_insert_iterator that inserts elements after the last element in a container.

explicit back_insert_iterator(Container& _Cont);

Parameters

_Cont
The container that the back_insert_iterator is to insert an element into.

Return Value

A back_insert_iterator for the parameter container.

Example

// back_insert_iterator_back_insert_iterator.cpp
// compile with: /EHsc
#include <iterator>
#include <vector>
#include <iostream>

int main( )
{
   using namespace std;
   int i;

   vector<int> vec;
   for ( i = 1 ; i < 4 ; ++i )
   {
      vec.push_back ( i );
   }

   vector <int>::iterator vIter;
   cout << "The initial vector vec is: ( ";
   for ( vIter = vec.begin ( ) ; vIter != vec.end ( ); vIter++)
      cout << *vIter << " ";
   cout << ")." << endl;

   // Insertions with member function
   back_inserter ( vec ) = 40;
   back_inserter ( vec ) = 50;

   // Alternatively, insertions can be done with template function
   back_insert_iterator<vector<int> > backiter ( vec );
*backiter = 600;
   backiter++;
*backiter = 700;

   cout << "After the insertions, the vector vec is: ( ";
   for ( vIter = vec.begin ( ) ; vIter != vec.end ( ); vIter++)
      cout << *vIter << " ";
   cout << ")." << endl;
}

The initial vector vec is: ( 1 2 3 ).
After the insertions, the vector vec is: ( 1 2 3 40 50 600 700 ).

back_insert_iterator::container_type

A type that provides a container for the back_insert_iterator.

typedef Container
container_type;

Remarks

The type is a synonym for the template parameter Container.

Example

// back_insert_iterator_container_type.cpp
// compile with: /EHsc
#include <iterator>
#include <vector>
#include <iostream>

int main( )
{
   using namespace std;
   int i;

   vector<int> vec;
   for (i = 1 ; i < 4 ; ++i )
   {
      vec.push_back (  i );
   }

   vector <int>::iterator vIter;
   cout << "The original vector vec is: ( ";
   for ( vIter = vec.begin ( ) ; vIter != vec.end ( ); vIter++)
      cout << *vIter << " ";
   cout << ")." << endl;

   back_insert_iterator<vector<int> >::container_type vec1 = vec;
   back_inserter ( vec1 ) = 40;

   cout << "After the insertion, the vector is: ( ";
   for ( vIter = vec1.begin ( ) ; vIter != vec1.end ( ); vIter++)
      cout << *vIter << " ";
   cout << ")." << endl;
}

The original vector vec is: ( 1 2 3 ).
After the insertion, the vector is: ( 1 2 3 40 ).

back_insert_iterator::operator*

Dereferencing operator used to implement the output iterator expression * i = x.

back_insert_iterator<Container>& operator*();

Return Value

A reference to the element inserted at the back of the container.

Remarks

Used to implement the output iterator expression *Iter = value. If Iter is an iterator that addresses an element in a sequence, then *Iter = value replaces that element with value and doesn't change the total number of elements in the sequence.

Example

// back_insert_iterator_back_insert.cpp
// compile with: /EHsc
#include <iterator>
#include <vector>
#include <iostream>

int main( )
{
   using namespace std;
   int i;

   vector<int> vec;
   for (i = 1 ; i < 4 ; ++i )
   {
      vec.push_back ( i );
   }

   vector <int>::iterator vIter;
   cout << "The vector vec is: ( ";
   for ( vIter = vec.begin ( ) ; vIter != vec.end ( ); vIter++)
      cout << *vIter << " ";
   cout << ")." << endl;

   back_insert_iterator<vector<int> > backiter ( vec );
*backiter = 10;
   backiter++;      // Increment to the next element
*backiter = 20;
   backiter++;

   cout << "After the insertions, the vector vec becomes: ( ";
   for ( vIter = vec.begin ( ) ; vIter != vec.end ( ); vIter++)
      cout << *vIter << " ";
   cout << ")." << endl;
}

The vector vec is: ( 1 2 3 ).
After the insertions, the vector vec becomes: ( 1 2 3 10 20 ).

back_insert_iterator::operator++

Increments the back_insert_iterator to the next location into which a value may be stored.

back_insert_iterator<Container>& operator++();
back_insert_iterator<Container> operator++(int);

Return Value

A back_insert_iterator addressing the next location into which a value may be stored.

Remarks

Both preincrementation and postincrementation operators return the same result.

Example

// back_insert_iterator_op_incre.cpp
// compile with: /EHsc
#include <iterator>
#include <vector>
#include <iostream>

int main( )
{
   using namespace std;
   int i;

   vector<int> vec;
   for (i = 1 ; i < 3 ; ++i )
   {
      vec.push_back ( 10 * i );
   }

   vector <int>::iterator vIter;
   cout << "The vector vec is: ( ";
   for ( vIter = vec.begin ( ) ; vIter != vec.end ( ); vIter++)
      cout << *vIter << " ";
   cout << ")." << endl;

   back_insert_iterator<vector<int> > backiter ( vec );
*backiter = 30;
   backiter++;      // Increment to the next element
*backiter = 40;
   backiter++;

   cout << "After the insertions, the vector vec becomes: ( ";
   for ( vIter = vec.begin ( ) ; vIter != vec.end ( ); vIter++)
      cout << *vIter << " ";
   cout << ")." << endl;
}

The vector vec is: ( 10 20 ).
After the insertions, the vector vec becomes: ( 10 20 30 40 ).

back_insert_iterator::operator=

Appends or pushes a value onto the back end of a container.

back_insert_iterator<Container>& operator=(typename Container::const_reference val);
back_insert_iterator<Container>& operator=(typename Container::value_type&& val);

Parameters

val
The value to be inserted into the container.

Return Value

A reference to the last element inserted at the back of the container.

Remarks

The first member operator evaluates Container.push_back( val),

then returns *this. The second member operator evaluates

container->push_back((typename Container::value_type&&)val),

then returns *this.

Example

// back_insert_iterator_op_assign.cpp
// compile with: /EHsc
#include <iterator>
#include <vector>
#include <iostream>

int main( )
{
   using namespace std;
   int i;

   vector<int> vec;
   for (i = 1 ; i < 4 ; ++i )
   {
      vec.push_back ( i );
   }

   vector <int>::iterator vIter;
   cout << "The vector vec is: ( ";
   for ( vIter = vec.begin ( ) ; vIter != vec.end ( ); vIter++)
      cout << *vIter << " ";
   cout << ")." << endl;

   back_insert_iterator<vector<int> > backiter ( vec );
*backiter = 10;
   backiter++;      // Increment to the next element
*backiter = 20;
   backiter++;

   cout << "After the insertions, the vector vec becomes: ( ";
   for ( vIter = vec.begin ( ) ; vIter != vec.end ( ); vIter++)
      cout << *vIter << " ";
   cout << ")." << endl;
}

back_insert_iterator::reference

A type that provides a reference for the back_insert_iterator.

typedef typename Container::reference reference;

Remarks

The type describes a reference to an element of the sequence controlled by the associated container.

Example

// back_insert_iterator_reference.cpp
// compile with: /EHsc
#include <iterator>
#include <vector>
#include <iostream>

int main( )
{
   using namespace std;
   int i;

   vector<int> vec;
   for (i = 1 ; i < 4 ; ++i )
   {
      vec.push_back ( i );
   }

   vector <int>::iterator vIter;
   cout << "The vector vec is: ( ";
   for ( vIter = vec.begin ( ) ; vIter != vec.end ( ); vIter++)
      cout << *vIter << " ";
   cout << ")." << endl;

   back_insert_iterator<vector<int> >::reference
        RefLast = *(vec.end ( ) - 1 );
   cout << "The last element in the vector vec is: "
        << RefLast << "." << endl;
}

The vector vec is: ( 1 2 3 ).
The last element in the vector vec is: 3.

See also

<iterator>
Thread Safety in the C++ Standard Library
C++ Standard Library Reference