back-insert-iterator-class.md

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Learn more about: back_insert_iterator Class	back_insert_iterator Class	06/07/2022	iterator/std::back_insert_iterator iterator/std::back_insert_iterator::container_type iterator/std::back_insert_iterator::reference	std::back_insert_iterator [C++] std::back_insert_iterator [C++], container_type std::back_insert_iterator [C++], reference	a1ee07f2-cf9f-46a1-8608-cfaf207f9713	devdivchpfy22

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 <classContainer> classback_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.

explicitback_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>intmain( ) { usingnamespacestd;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 functionback_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>intmain( ) { usingnamespacestd;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>intmain( ) { usingnamespacestd;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>intmain( ) { usingnamespacestd;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>intmain( ) { usingnamespacestd;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.

typedeftypename 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>intmain( ) { usingnamespacestd;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