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    cpp/iterator/back insert iterator: Difference between revisions

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    Line 47: Line 47:
    #include <iterator>
    #include <iterator>
    #include <algorithm>
    #include <algorithm>
    #include <cstdlib>
    #include <vector>
    #include <vector>


    Line 54: Line 53:
         std::vector<int> v;
         std::vector<int> v;
         std::generate_n(std::back_insert_iterator<std::vector<int>>(v), // can be simplified
         std::generate_n(std::back_insert_iterator<std::vector<int>>(v), // can be simplified
                         10, [](){ return std::rand() % 10; });        // with std::back_inserter
                         10, []() { return ; });        // with std::back_inserter
         for (int n : v)
         for (int n : v)
             std::cout << n << ' ';
             std::cout << n << ' ';
    Line 60: Line 59:
    }
    }
      | output=
      | output=
    3 6 7 5 3 5 6 2 9 1
    3 6 7 9
    }}
    }}


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    {{dsc end}}
    {{dsc end}}


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    Revision as of 03:56, 6 May 2018

     
    C++
     
    Iterator library
    Iterator concepts
    Iterator primitives
    Algorithm concepts and utilities
    Indirect callable concepts
    Common algorithm requirements
    (C++20)
    (C++20)
    (C++20)
    Utilities
    (C++20)
    Iterator adaptors
    Range access
    (C++11)(C++14)
    (C++14)(C++14)  
    (C++11)(C++14)
    (C++14)(C++14)  
    (C++17)(C++20)
    (C++17)
    (C++17)
     
    std::back_insert_iterator
     
    Defined in header <iterator> 
    template< class Container >
class back_insert_iterator : public std::iterator< std::output_iterator_tag,
                                                   void, void, void, void >
    		(until C++17) 
    template< class Container >
class back_insert_iterator;
    		(since C++17)

    std::back_insert_iterator is an Template:concept that appends to a container for which it was constructed. The container's push_back() member function is called whenever the iterator (whether dereferenced or not) is assigned to. Incrementing the std::back_insert_iterator is a no-op.

    Member types

    Member type Definition
    container_type Container

    Member functions

    		 constructs a new back_insert_iterator
    (public member function) [edit]
    		inserts an object into the associated container
    (public member function) [edit]
    		no-op
    (public member function) [edit]
    		no-op
    (public member function) [edit]

    Member objects

    Member name Definition
    container (protected) a pointer of type Container*

    Member types

    Member type Definition
    iterator_category std::output_iterator_tag
    value_type void
    difference_type

    void

    		(until C++20)

    std::ptrdiff_t

    		(since C++20)
    pointer void
    reference void

    Member types iterator_category, value_type, difference_type, pointer and reference are required to be obtained by inheriting from std::iterator<std::output_iterator_tag, void, void, void, void>.

    		(until C++17)

    Example

    Run this code
    #include <iostream>
#include <iterator>
#include <algorithm>
#include <vector>

int main()
{
    std::vector<int> v;
    std::generate_n(std::back_insert_iterator<std::vector<int>>(v), // can be simplified
                    10, [n=0]() mutable { return ++n; });        // with std::back_inserter
    for (int n : v)
        std::cout << n << ' ';
    std::cout << '\n';
}

    Output: 

    1 2 3 4 5 6 7 8 9 10

    See also

    		 creates a std::back_insert_iterator of type inferred from the argument
    (function template) [edit]
    		iterator adaptor for insertion at the front of a container
    (class template) [edit]
    		iterator adaptor for insertion into a container
    (class template) [edit]