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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:
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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;
};
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Template parameters
- Category
- Category to which the iterator belongs to. It must be one of the following iterator tags:
- 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
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// 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) {myiterator tmp(*this); operator++(); return tmp;}
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;
}
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Output
See also
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