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std::iterator

From cppreference.com
< cpp‎ | iterator
 
 
Iterator library
Iterator concepts
(C++20)
(C++20)
(C++20)
(C++20)
Iterator primitives
Iterator adaptors
Stream iterators
Iterator customization points
Iterator operations
(C++11)
(C++11)
Range access
(C++11)(C++14)
(C++11)(C++14)
(C++17)(C++20)
(C++14)(C++14)
(C++14)(C++14)
(C++17)
(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.

Contents

[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 {
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

[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]