NAME¶

std::iterator - std::iterator

Synopsis¶

Defined in header <iterator>
template<

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

Example¶

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

// Run this code

#include <iostream>
#include <algorithm>

template<long FROM, long TO>
class Range {
public:
// 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;
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 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';
}

Output:¶

18
3 4 5

See also¶

provides uniform interface to the properties of an
iterator_traits iterator
(class template)
input_iterator_tag
output_iterator_tag
forward_iterator_tag empty class types used to indicate iterator categories
bidirectional_iterator_tag (class)
random_access_iterator_tag
contiguous_iterator_tag
(C++20)