list实现

//链表结点结构
template <class T>
struct _list_node
{
    typedef void *void_pointer;
    //指针类型为void *,其实可以设为_list_node<T>*
    void_pointer prev;
    void_pointer next;
    T data;
};

/*
迭代器有五种类型，Input Iterator,output Iterator,Forward Iterator只支持++，Biderectional Iterator支持++、--,Random Access Iterator支持
所有运算，效率最高
*/
struct input_iterator_tag{};
struct output_iterator_tag{};
struct forward_iterator_tag :public input_iterator_tag{};
struct bidirectional_iterator_tag :public forward_iterator_tag{};
struct random_access_iterator_tag :public bidirectional_iterator_tag{};

//list迭代器设计
template <class T,class Ref,class Ptr>
struct _list_iterator
{
    typedef _list_iterator<T, T&, T*> iterator;
    typedef _list_iterator<T, Ref, Ptr>self;

    //traits萃取
    typedef bidirectional_iterator_tag iterator_category;
    typedef T value_type;
    typedef Ptr pointer;
    typedef Ref reference;
    typedef ptrdiff_t difference_type;
    typedef _list_node<T>* link_type;
    typedef size_t size_type;

    link_type node;//迭代器内部的普通指针，指向list的结点

    //构造函数
    _list_iterator(link_type x) :node(x){}
    _list_iterator(){}
    _list_iterator(const iterator& x) :node(x.node){}

    reference operator*()const
    {
        return (*node).data;
    }
    pointer operator->()const
    {
        return &(operator*());
    }

    //前增量
    self &operator++()
    {
        node = (link_type)((*node).next);
        return *this;
    }
    //后增量
    self operator++(int)
    {
        self tmp = *this;
        ++*this;
        return tmp;
    }

    self &operator--()
    {
        node = (link_type)((*node).prev);
        return *this;
    }

    self operator--(int)
    {
        self tmp = *this;
        --*this;
        return tmp;
    }
};

//SGI list是一个环状双向链表
template<class T,class Alloc=alloc>
class list
{
protected:
    typedef _list_node<T> list_node;
public:
    typedef list_node* link_type;

protected:
    link_type node;//该指针表示整个环状双向链表，可使其指向置于尾端的一个空白结点
    //list缺省使用alloc作为空间配置器，并据此另外定义了list_node_allocator,为的是更方便地以节点大小为配置单位
    typedef simple_alloc<list_node, Alloc>list_node_allocator;
};