insert_iterator Class

Article
06/17/2022

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

Syntax

template <class Container>
class insert_iterator;

Parameters

Container
The type of container into which elements are to be inserted by an insert_iterator.

Remarks

The container of type Container must satisfy the requirements for a variable-sized container and have a two-argument insert member function where the parameters are of type Container::iterator and Container::value_type and that returns a type Container::iterator. C++ Standard Library sequence and sorted associative containers satisfy these requirements and can be adapted to use with insert_iterators. For associative containers, the position argument is treated as a hint, which has the potential to improve or degrade performance depending on how good the hint is. An insert_iterator must always be initialized with its container.

Constructors

Constructor	Description
insert_iterator	Constructs an `insert_iterator` that inserts an element into a specified position in a container.

Typedefs

Type name	Description
container_type	A type that represents the container into which a general insertion is to be made.
reference	A type that provides a reference to an element in a sequence controlled by the associated container.

Operators

Operator	Description
operator*	Dereferencing operator used to implement the output iterator expression * `i` = `x` for a general insertion.
operator++	Increments the `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 general insertion.

Requirements

Header: <iterator>

Namespace: std

insert_iterator::container_type

A type that represents the container into which a general insertion is to be made.

typedef Container container_type;

Remarks

The type is a synonym for the template parameter Container.

Example

// insert_iterator_container_type.cpp
// compile with: /EHsc
#include <iterator>
#include <list>
#include <iostream>

int main( )
{
   using namespace std;

   list<int> L1;
   insert_iterator<list<int> >::container_type L2 = L1;
   inserter ( L2, L2.end ( ) ) = 20;
   inserter ( L2, L2.end ( ) ) = 10;
   inserter ( L2, L2.begin ( ) ) = 40;

   list <int>::iterator vIter;
   cout << "The list L2 is: ( ";
   for ( vIter = L2.begin ( ) ; vIter != L2.end ( ); vIter++ )
      cout << *vIter << " ";
   cout << ")." << endl;
}
/* Output:
The list L2 is: ( 40 20 10 ).
*/

insert_iterator::insert_iterator

Constructs an insert_iterator that inserts an element into a specified position in a container.

insert_iterator(Container& _Cont, typename Container::iterator _It);

Parameters

_Cont
The container into which the insert_iterator is to insert elements.

_It
The position for the insertion.

Remarks

All containers have the insert member function called by the insert_iterator. For associative containers the position parameter is merely a suggestion. The inserter function provides a convenient way to insert to values.

Example

// insert_iterator_insert_iterator.cpp
// compile with: /EHsc
#include <iterator>
#include <list>
#include <iostream>

int main( )
{
   using namespace std;
   int i;
   list <int>::iterator L_Iter;

   list<int> L;
   for (i = 1 ; i < 4 ; ++i )
   {
      L.push_back ( 10 * i );
   }

   cout << "The list L is:\n ( ";
   for ( L_Iter = L.begin( ) ; L_Iter != L.end( ); L_Iter++)
      cout << *L_Iter << " ";
   cout << ")." << endl;

   // Using the member function to insert an element
   inserter ( L, L.begin ( ) ) = 2;

   // Alternatively, you may use the template version
   insert_iterator< list < int> > Iter(L, L.end ( ) );
*Iter = 300;

   cout << "After the insertions, the list L is:\n ( ";
   for ( L_Iter = L.begin( ) ; L_Iter != L.end( ); L_Iter++ )
      cout << *L_Iter << " ";
   cout << ")." << endl;
}
/* Output:
The list L is:
( 10 20 30 ).
After the insertions, the list L is:
( 2 10 20 30 300 ).
*/

insert_iterator::operator*

Dereferences the insert iterator returning the element is addresses.

insert_iterator<Container>& operator*();

Return Value

The member function returns the value of the element addressed.

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

// insert_iterator_op_deref.cpp
// compile with: /EHsc
#include <iterator>
#include <list>
#include <iostream>

int main( )
{
   using namespace std;
   int i;
   list <int>::iterator L_Iter;

   list<int> L;
   for (i = 0 ; i < 4 ; ++i )
   {
      L.push_back ( 2 * i );
   }

   cout << "The original list L is:\n ( ";
   for ( L_Iter = L.begin( ) ; L_Iter != L.end( ); L_Iter++ )
      cout << *L_Iter << " ";
   cout << ")." << endl;

   insert_iterator< list < int> > Iter(L, L.begin ( ) );
*Iter = 10;
*Iter = 20;
*Iter = 30;

   cout << "After the insertions, the list L is:\n ( ";
   for ( L_Iter = L.begin( ) ; L_Iter != L.end( ); L_Iter++ )
      cout << *L_Iter << " ";
   cout << ")." << endl;
}
/* Output:
The original list L is:
( 0 2 4 6 ).
After the insertions, the list L is:
( 10 20 30 0 2 4 6 ).
*/

insert_iterator::operator++

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

insert_iterator<Container>& operator++();

insert_iterator<Container> operator++(int);

Parameters

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

Remarks

Both preincrementation and postincrementation operators return the same result.

Example

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

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

   vector<int> vec;
   for (i = 1 ; i < 5 ; ++i )
   {
      vec.push_back (  i );
   }

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

   insert_iterator<vector<int> > ii ( vec, vec.begin ( ) );
*ii = 30;
   ii++;
*ii = 40;
   ii++;
*ii = 50;

   cout << "After the insertions, the vector vec becomes:\n ( ";
   for ( vIter = vec.begin ( ) ; vIter != vec.end ( ); vIter++ )
      cout << *vIter << " ";
   cout << ")." << endl;
}
/* Output:
The vector vec is:
( 1 2 3 4 ).
After the insertions, the vector vec becomes:
( 30 40 50 1 2 3 4 ).
*/

insert_iterator::operator=

Inserts a value into the container and returns the iterator updated to point to the new element.

insert_iterator<Container>& operator=(
    typename Container::const_reference val,);

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

Parameters

val
The value to be assigned to the container.

Return Value

A reference to the element inserted into the container.

Remarks

The first member operator evaluates

Iter = container->insert(Iter, val);

++Iter;

then returns *this.

The second member operator evaluates

Iter = container->insert(Iter, std::move(val));

++Iter;

then returns *this.

Example

// insert_iterator_op_assign.cpp
// compile with: /EHsc
#include <iterator>
#include <list>
#include <iostream>

int main( )
{
   using namespace std;
   int i;
   list <int>::iterator L_Iter;

   list<int> L;
   for (i = 0 ; i < 4 ; ++i )
   {
      L.push_back ( 2 * i );
   }

   cout << "The original list L is:\n ( ";
   for ( L_Iter = L.begin( ) ; L_Iter != L.end( ); L_Iter++ )
      cout << *L_Iter << " ";
   cout << ")." << endl;

   insert_iterator< list < int> > Iter(L, L.begin ( ) );
*Iter = 10;
*Iter = 20;
*Iter = 30;

   cout << "After the insertions, the list L is:\n ( ";
   for ( L_Iter = L.begin( ) ; L_Iter != L.end( ); L_Iter++ )
      cout << *L_Iter << " ";
   cout << ")." << endl;
}
/* Output:
The original list L is:
( 0 2 4 6 ).
After the insertions, the list L is:
( 10 20 30 0 2 4 6 ).
*/

insert_iterator::reference

A type that provides a reference to an element in a sequence controlled by the associated container.

typedef typename Container::reference reference;

Remarks

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

Example

// insert_iterator_container_reference.cpp
// compile with: /EHsc
#include <iterator>
#include <list>
#include <iostream>

int main( )
{
   using namespace std;

   list<int> L;
   insert_iterator<list<int> > iivIter( L , L.begin ( ) );
*iivIter = 10;
*iivIter = 20;
*iivIter = 30;

   list<int>::iterator LIter;
   cout << "The list L is: ( ";
   for ( LIter = L.begin ( ) ; LIter != L.end ( ); LIter++ )
      cout << *LIter << " ";
   cout << ")." << endl;

   insert_iterator<list<int> >::reference
        RefFirst = *(L.begin ( ));
   cout << "The first element in the list L is: "
        << RefFirst << "." << endl;
}
/* Output:
The list L is: ( 10 20 30 ).
The first element in the list L is: 10.
*/

insert_iterator Class

Syntax

Parameters

Remarks

Constructors

Typedefs

Operators

Requirements

insert_iterator::container_type

Remarks

Example

insert_iterator::insert_iterator

Parameters

Remarks

Example

insert_iterator::operator*

Return Value

Remarks

Example

insert_iterator::operator++

Parameters

Remarks

Example

insert_iterator::operator=

Parameters

Return Value

Remarks

Example

insert_iterator::reference

Remarks

Example

See also

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