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std::iterator(3)	      C++ Standard Libary	      std::iterator(3)

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 derefer-
       encing the
		      iterator.	This type should be void for output iterators.
	  Distance  - a	type that can be used to identify distance between it-
       erators
	  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_cate-
       gory
				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 proper-
       ties of an
	  iterator_traits	     iterator
				     (class template)
	  input_iterator_tag
	  output_iterator_tag
	  forward_iterator_tag	     empty class types used to indicate	itera-
       tor categories
	  bidirectional_iterator_tag (class)
	  random_access_iterator_tag
	  contiguous_iterator_tag
	  (C++20)

http://cppreference.com		  2022.07.31		      std::iterator(3)

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