back_insert_iterator

Overview

The STL algorithms usually overwrite elements of the range passed to them as parameters. Instead, sometimes it's useful to append new elements to the range. back_insert_iterator is designed exactly to do it.

Details

A back-insert_iterator is a special output iterator which can be  generated from the container that supports push_back() operation. such as standard containers vector, deque and list.

Syntax

The syntax is as below. Template parameter Container represents the container that is updated. 

template < class Container > 
class  back_insert_iterator;

Members

 It defines following types.

member type	definition
conainer_type	Container
iterator_category	output_iterator_tag
value_type	void
difference_type	void
pointer	void
reference	void

Operation

An back_insert_iterator supports three operators *, ++ and =. 

The assignment operator, used both during dereferencing or directly, causes the container to expand by one element. For example, both *i = x and i=x adds a new element.

Dereferencing operator does nothing.

Both pre and post Increments the back_insert_iterator does nothing.

This can be clearly seen in the example below. 

vector<int> v{1,2,3,4};
back_insert_iterator<vector<int> > backiter ( v );

//v:{1,2,3,4,6}
*backiter = 6;

//v:{1,2,3,4,6,7}
backiter = 7;

Functionality

Constructors

Name	Description
back_insert_iterator(Container& c)	Initializes the underlying pointer to the container to addressof(c). Example: vector<int> v{1, 2, 3, 4, 5}; back_insert_iterator<vector<int>> backiter (v);

Overloaded operators

Name	Example
reference operator* ()	No Operation.
back_insert_iterator& operator++() back_insert_iterator& operator++(int)	No Operation.
pointer operator=()	Appends a new element Example: vector<int> v{1,2,3,4}; back_insert_iterator<vector<int> > backiter ( v ); //v:{1,2,3,4,6} *backiter = 6; //v:{1,2,3,4,6,7} backiter = 7;

back_inserter

An utility function to create a back_insert_iterator from a container that supports push_back() method such as vector, deque, list.

Syntax

The syntax is as below. Template parameter Container represents the container for which 

back_inserter_iterator is created. Container represents must support push_back() function as in vector, deque and list.

template < class Container > 
back_insert_iterator<Container >  back_inserter( Container& c );

The following example shows its usage.

vector<int> v{1,2,3,4}, v2;
//same as 
//for_each(begin(v),end(v),[&v2](int i){v2.push_back(i);});
//v2:{1,2,3,4}
copy (v.begin(),v.end(),back_inserter(v2));