<iterator>

Iterator base class

This is a base class template that can be used to derive iterator classes from it. It is not an iterator class and does not provide any of the functionality an iterator is expected to have.

This base class only provides some member types, which in fact are not required to be present in any iterator type (iterator types have no specific member requirements), but they might be useful, since they define the members needed for the default iterator_traits class template to generate the appropriate iterator_traits class automatically.

It is defined as:

template <class Category, class T, class Distance = ptrdiff_t,
          class Pointer = T*, class Reference = T&>
  struct iterator {
    typedef T         value_type;
    typedef Distance  difference_type;
    typedef Pointer   pointer;
    typedef Reference reference;
    typedef Category  iterator_category;
  };

Template parameters

Category

Category to which the iterator belongs to. It must be one of the following iterator tags:

iterator tag	Category of iterators
input_iterator_tag	Input Iterator
output_iterator_tag	Output Iterator
forward_iterator_tag	Forward Iterator
bidirectional_iterator_tag	Bidirectional Iterator
random_access_iterator_tag	Random Access Iterator

T

Type of elements pointed by the iterator.

Distance

Type to represent the difference between two iterators.

Pointer

Type to represent a pointer to an element pointed by the iterator.

Reference

Type to represent a reference to an element pointed by the iterator.

Example

// iterator example
#include <iostream>
#include <iterator>
using namespace std;

class myiterator : public iterator<input_iterator_tag, int>
{
  int* p;
public:
  myiterator(int* x) :p(x) {}
  myiterator(const myiterator& mit) : p(mit.p) {}
  myiterator& operator++() {++p;return *this;}
  myiterator& operator++(int) {p++;return *this;}
  bool operator==(const myiterator& rhs) {return p==rhs.p;}
  bool operator!=(const myiterator& rhs) {return p!=rhs.p;}
  int& operator*() {return *p;}
};

int main () {
  int numbers[]={10,20,30,40,50};
  myiterator beginning(numbers);
  myiterator end(numbers+5);
  for (myiterator it=beginning; it!=end; it++)
	  cout << *it << " ";
  cout << endl;

  return 0;
}

Output

10 20 30 40 50

See also