定义自己的迭代器的步骤
基本上iterator必须做两件事情
1)必须指向某物
2)他必须能够遍历任何一个有效区间。一旦定义了operator* operator++通常剩下的行为就比较简单了。
必须确定iterator被正确的定义为constant或者mutable。这是常犯的错误之一。不过input iterator不在乎这一点，因为具有只读性。outputIterator具有只写性。
对于其他的类型的iterator就不一样了
定义自己的Iterator时，必须定义五个嵌套类型，iterator_category、value_type、difference_type、pointer和reference。
STL含有一个辅助类，base class iterator,
An empty base class that provides types and that may be used to ensure that a user-defines iterator class works properly with iterator_traits.
template<class Category, class Type, class Distance = ptrdiff_t
class Pointer = Type*, class Reference = Type&>
struct iterator {
typedef Category iterator_category;
typedef Type value_type;
typedef Distance difference_type;
typedef Pointer pointer;
typedef Reference reference;
};
Remarks
The template class serves as a base type for all iterators. It defines the member types
-
iterator_category (a synonym for the template parameter Category).
-
value_type (a synonym for the template parameter Type).
-
difference_type (a synonym for the template parameter Distance).
-
pointer (a synonym for the template parameter Pointer).
-
reference (a synonym for the template parameter Reference).
Note that value_type should not be a constant type even if pointer points at an object of const Type and reference designates an object of const Type.
下面是一个iterator的完整定义和使用
#include "stdafx.h"
#include <iterator>
using namespace std;
//下面函数主要来定义迭代器，一个专门针对还含有next的铁代器
template <typename Node, typename Reference = Node&, typename Pointer = Node*>
struct node_wrap_base_iterator:public iterator<forward_iterator_tag,Node,ptrdiff_t,Pointer,Reference>
{
typedef node_wrap_base_iterator<Node,Node&,Node*> iterator;
typedef node_wrap_base_iterator<Node,const Node&,const Node*> const_iterator;
Pointer ptr;
node_wrap_base_iterator(Pointer p = 0):ptr(p){}
node_wrap_base_iterator(const iterator& x):ptr(x.ptr){}
Reference operator*()const{return *ptr;}
Pointer operator->()const{return ptr;}
void incr(){ptr=ptr->next;}
node_wrap_base_iterator& operator++(){incr(); return *this;}
node_wrap_base_iterator operator++(int){node_wrap_base_iterator tmp=*this;incr();return tmp;}
bool operator==(const node_wrap_base_iterator& x) const {return ptr==x.ptr;}
bool operator!=(const node_wrap_base_iterator& x) const {return ptr!=x.ptr;}
};
测试：
typedef struct Node
{
int value;
Node* next;
}Node;
//重载<<
ostream& operator<<(ostream & out,Node node)
{
out<<node.value;
return out;
}
//使用迭代器
template<typename iterator>
void display(iterator begin,iterator end)
{
iterator tmp = begin;
while(tmp!=end&&tmp!=NULL)
{
cout<<*tmp<<" ";
tmp++;
}
cout<<endl;
}
template <typename Iterator>
//学习使用iterator_traits
typename iterator_traits<Iterator>::value_type test_traits(Iterator iter)
{
return *iter;
}
#define N 10
typedef node_wrap_base_iterator<Node>::iterator node_iterator;
int _tmain(int argc, _TCHAR* argv[])
{
Node node[N];
for(int i=0; i<N;i++)
{
node[i].value=i;
if(i < N-1)
node[i].next=&node[i+1];
else
node[i].next=NULL;
}
node_iterator beg(node);
node_iterator end(node+N);
display(beg,end);
Node test;
test.value=11;
test.next=NULL;
node_iterator iter(&test);
cout<<test_traits(iter);
cout<<endl;
return 0;
}
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