std::iterator

 

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Iterator library

Iterator concepts
indirectly_readable (C++20) indirectly_writable (C++20) weakly_incrementable (C++20) incrementable (C++20) is-integer-like is-signed-integer-like (C++20)(C++20)	sentinel_for (C++20) sized_sentinel_for (C++20) input_iterator (C++20) output_iterator (C++20) input_or_output_iterator (C++20)	forward_iterator (C++20) bidirectional_iterator (C++20) random_access_iterator (C++20) contiguous_iterator (C++20)
Iterator primitives
input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag (C++20)	iter_value_titer_difference_titer_reference_titer_const_reference_titer_rvalue_reference_titer_common_reference_t (C++20)(C++20)(C++20)(C++23)(C++20)(C++20)	iterator (deprecated in C++17) iterator_traits incrementable_traits (C++20) indirectly_readable_traits (C++20)
Algorithm concepts and utilities
Indirect callable concepts
indirectly_unary_invocableindirectly_regular_unary_invocable (C++20)(C++20)	indirect_unary_predicate (C++20) indirect_binary_predicate (C++20)	indirect_equivalence_relation (C++20) indirect_strict_weak_order (C++20)
Common algorithm requirements
indirectly_movable (C++20) indirectly_movable_storable (C++20) indirectly_copyable (C++20)	indirectly_copyable_storable (C++20)   indirectly_swappable (C++20) indirectly_comparable (C++20)	permutable (C++20) mergeable (C++20) sortable (C++20)
Utilities
indirect_result_t (C++20)	projected (C++20)	projected_value_t (C++26)
Iterator adaptors
reverse_iterator make_reverse_iterator (C++14) move_iterator (C++11) make_move_iterator (C++11) default_sentinel_tdefault_sentinel (C++20)(C++20) unreachable_sentinel_tunreachable_sentinel (C++20)(C++20)	front_insert_iterator back_insert_iterator inserter insert_iterator front_inserter back_inserter move_sentinel (C++20)	common_iterator (C++20) counted_iterator (C++20) basic_const_iterator (C++23) const_iterator (C++23) const_sentinel (C++23) make_const_iterator (C++23) make_const_sentinel (C++23)
Stream iterators istream_iterator    ostream_iterator istreambuf_iterator ostreambuf_iterator	Iterator customization points ranges::iter_move (C++20) ranges::iter_swap (C++20)
Iterator operations advance distance prev (C++11)   next (C++11) ranges::advance (C++20) ranges::distance (C++20) ranges::prev (C++20) ranges::next (C++20)	Range access begincbegin (C++11)(C++14) rbegincrbegin (C++14)(C++14)   endcend (C++11)(C++14) rendcrend (C++14)(C++14)   sizessize (C++17)(C++20) empty (C++17) data (C++17)

 

Defined in header <iterator>
template<     class Category,     class T,     class Distance =std::ptrdiff_t,     class Pointer = T*,     class Reference = T& >struct iterator;		(deprecated in C++17)

std::iterator is the base class provided to simplify definitions of the required types for iterators.

Template parameters

Category	-	the category of the iterator. Must be one of iterator category tags.
T	-	the type of the values that can be obtained by dereferencing the iterator. This type should be void for output iterators.
Distance	-	a type that can be used to identify distance between iterators
Pointer	-	defines a pointer to the type iterated over (T)
Reference	-	defines a reference to the type iterated over (T)

Member types

Member type	Definition
iterator_category	Category
value_type	T
difference_type	Distance
pointer	Pointer
reference	Reference

Example

The following example shows how to implement an input iterator by inheriting from std::iterator

Run this code

#include <algorithm>#include <iostream>   template<long FROM, long TO>class Range {public:// member typedefs provided through inheriting from std::iteratorclass iterator :public std::iterator<std::input_iterator_tag, // iterator_categorylong, // value_typelong, // difference_typeconstlong*, // pointerlong// reference>{long num = FROM;public:explicit iterator(long _num =0): num(_num){} iterator& operator++(){ num = TO >= FROM ? num +1: num -1;return*this;} iterator operator++(int){ iterator retval =*this;++(*this);return retval;}bool operator==(iterator other)const{return num == other.num;}bool operator!=(iterator other)const{return!(*this == other);} reference operator*()const{return num;}}; iterator begin(){return iterator(FROM);} iterator end(){return iterator(TO >= FROM? TO +1: TO -1);}};   int main(){// std::find requires an input iteratorauto range = Range<15, 25>();auto itr =std::find(range.begin(), range.end(), 18);std::cout<<*itr <<'\n';// 18   // Range::iterator also satisfies range-based for requirementsfor(long l : Range<3, 5>())std::cout<< l <<' ';// 3 4 5std::cout<<'\n';}

Output:

18 3 4 5

See also

iterator_traits	provides uniform interface to the properties of an iterator (class template)
input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag (C++20)	empty class types used to indicate iterator categories (class)