std::iterator (3) - Linux Manuals

std::iterator: std::iterator


std::iterator - std::iterator


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

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


The following example shows how to implement a input_iterator by inheriting from std::iterator
// Run this code

  #include <iostream>
  #include <algorithm>

  template<long FROM, long TO>
  class Range {
      // member typedefs provided through inheriting from std::iterator
      class iterator: public std::iterator<
                          std::input_iterator_tag, // iterator_category
                          long, // value_type
                          long, // difference_type
                          const long*, // pointer
                          long // reference
          long num = FROM;
          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 iterator
      auto 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 requirements
      for(long l : Range<3, 5>()) {
          std::cout << l << ' '; // 3 4 5
      std::cout << '\n';


  3 4 5

See also

                           provides uniform interface to the properties of an iterator
iterator_traits (class template)

contiguous_iterator_tag empty class types used to indicate iterator categories