< cpp‎ | iterator
Iterator library
Iterator concepts
Iterator primitives
Algorithm concepts and utilities
Indirect callable concepts
Common algorithm requirements
Iterator adaptors
Stream iterators
Iterator customization points
Iterator operations
Range access
Defined in header <iterator>

    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.


[edit] 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)

[edit] Member types

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

[edit] Example

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

#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

[edit] See also

provides uniform interface to the properties of an iterator
(class template) [edit]
empty class types used to indicate iterator categories
(class) [edit]