理解iterator

參考：http://www.cplusplus.com/reference/std/iterator/iterator/

// 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;
}
//Output: 10 20 30 40 50

MSDN中的iterator

iterator
template<class C, class T, class Dist = ptrdiff_t>
struct iterator {
    typedef C iterator_category;
    typedef T value_type;
    typedef Dist distance_type;
};
The template class serves as a base type for all iterators. It defines the member types 
iterator_category (a synonym(synonym同義詞) for the template parameter C), 
value_type (a synonym for the template parameter T), 
and distance_type (a synonym for the template parameter Dist).

表示iterator是其他所有迭代器的一個基本類型。

來自http://www.cplusplus.com/reference/std/iterator/iterator/中的iterator

iterator 是一個類模板。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.

iterator的定義如下：

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;
  };

參數說明如下：

TType of elements pointed by the iterator.DistanceType to represent the difference between two iterators.PointerType to represent a pointer to an element pointed by the iterator.ReferenceType to represent a reference to an element pointed by the iterator.CategoryCategory 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

請參見本文最上面的例子。