std::iterator - cppreference.com (original) (raw)
| | | | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | --------------------- | | 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.
[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 an input iterator by inheriting from std::iterator
#include #include 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: