STL源代码剖析 容器 stl_deque.h

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deque

------------------------------------------------------------------------

??一直看不懂 operator->() 。不明确它为什么不用接受參数。直接 return &(operator*())

好像我们用迭代器的时候也不没怎么用到这个函数，甚至我都不会用





1.概述

vector 是单向开口的连续线性空间。deque 则是一种双向开口的连续线性空间

同意常数时间内对起头端进行元素的插入和移除操作

没有容量概念。由于它是动态地以分段连续空间组合而成，随时能够添加一段新的空间并链接起来

deque 的迭代器不是普通指针，如非必要。应选择 vector 而非 deque

对deque 排序，可将 deque 先完整拷贝到一个 vector 身上，将 vector 排序后，再复制回 deque

图 4-9

2.deque 的中控器

map (不是 STL 里的 map 容器) --> 主控，是一小块连续空间。每一个元素指向还有一段较大的连续空间 node-buffer

node-buffer --> 存储空间主体

图 4-10

3.迭代器

cur --> 指出分段连续空间在哪里 

first, last --> 推断自己是否已经处于缓冲区的边缘

node --> 在缓冲区边缘前进或后退时必须知道中控器在哪

图4-11

图4-12

#ifndef __SGI_STL_INTERNAL_DEQUE_H
#define __SGI_STL_INTERNAL_DEQUE_H

__STL_BEGIN_NAMESPACE 

#if defined(__sgi) && !defined(__GNUC__) && (_MIPS_SIM != _MIPS_SIM_ABI32)
#pragma set woff 1174
#endif

// Note: this function is simply a kludge to work around several compilers'
//  bugs in handling constant expressions.
// 决定缓冲区大小
// 假设 n 不为 0。传回n ，表示 buffer size 由用户自己定义
// 假设 n 为 0，表示 buffer size 使用默认值，那么
// 	 假设 sz(元素大小，sizeof(value_type))小于512，返回 512/sz,
//	 假设 sz不小于 512。返回 1
inline size_t __deque_buf_size(size_t n, size_t sz)
{
  return n != 0 ? n : (sz < 512 ? size_t(512 / sz) : size_t(1));
}

#ifndef __STL_NON_TYPE_TMPL_PARAM_BUG
template <class T, class Ref, class Ptr, size_t BufSiz>
struct __deque_iterator {
  typedef __deque_iterator<T, T&, T*, BufSiz>             iterator;
  typedef __deque_iterator<T, const T&, const T*, BufSiz> const_iterator;
  static size_t buffer_size() {return __deque_buf_size(BufSiz, sizeof(T)); }
#else /* __STL_NON_TYPE_TMPL_PARAM_BUG */
template <class T, class Ref, class Ptr>
struct __deque_iterator {
  typedef __deque_iterator<T, T&, T*>             iterator;
  typedef __deque_iterator<T, const T&, const T*> const_iterator;
  static size_t buffer_size() {return __deque_buf_size(0, sizeof(T)); }
#endif

  typedef random_access_iterator_tag iterator_category;
  typedef T value_type;
  typedef Ptr pointer;
  typedef Ref reference;
  typedef size_t size_type;
  typedef ptrdiff_t difference_type;
  typedef T** map_pointer;

  typedef __deque_iterator self;

  T* cur; //指向缓冲区的现行元素
  T* first; //指向缓冲区的头
  T* last; // 指向缓冲区的尾

  map_pointer node; //指向中控器

  __deque_iterator(T* x, map_pointer y)
    : cur(x), first(*y), last(*y + buffer_size()), node(y) {}
  __deque_iterator() : cur(0), first(0), last(0), node(0) {}
  __deque_iterator(const iterator& x)
    : cur(x.cur), first(x.first), last(x.last), node(x.node) {}
  //解引用
  reference operator*() const { return *cur; }
#ifndef __SGI_STL_NO_ARROW_OPERATOR
  //？？好像没用过这东西
  pointer operator->() const { return &(operator*()); }
#endif /* __SGI_STL_NO_ARROW_OPERATOR */
  //两个迭代器之间的距离
  difference_type operator-(const self& x) const {
    return difference_type(buffer_size()) * (node - x.node - 1) +
      (cur - first) + (x.last - x.cur);
  }
  //前置++
  self& operator++() {
    ++cur;					//切换至下一个元素
    if (cur == last) {		//假设已达到所在缓冲区的尾端
      set_node(node + 1);	//就切换至下一缓冲区的第一个元素
      cur = first;
    }
    return *this;
  }
  //后置++
  self operator++(int)  {
    self tmp = *this;
    ++*this;				//调用前置++ 完毕前进 ?

--> yes
    return tmp;
  }
  //前置--
  self& operator--() {
    if (cur == first) {
      set_node(node - 1);
      cur = last;
    }
    --cur;
    return *this;
  }
  //后置--
  self operator--(int) {
    self tmp = *this;
    --*this;
    return tmp;
  }
  //随机存取
  self& operator+=(difference_type n) {
    difference_type offset = n + (cur - first);
	//目标位置在同一缓冲区
    if (offset >= 0 && offset < difference_type(buffer_size()))
      cur += n;
	//目标位置在不同缓冲区
    else {
      difference_type node_offset =
        offset > 0 ? offset / difference_type(buffer_size())
                   : -difference_type((-offset - 1) / buffer_size()) - 1;
      //切换至正确的节点(缓冲区)
	  set_node(node + node_offset);
	  //切换至正确的元素
      cur = first + (offset - node_offset * difference_type(buffer_size()));
    }
    return *this;
  }

  self operator+(difference_type n) const {
    self tmp = *this;
    return tmp += n; //? 不懂为什么是对 暂时变量 调用 operator+= --> 由于是 operator+，本来就不用改变 this 指向的对象
  }

  self& operator-=(difference_type n) { return *this += -n; }

  self operator-(difference_type n) const {
    self tmp = *this;
    return tmp -= n;
  }

  reference operator[](difference_type n) const { return *(*this + n); }

  bool operator==(const self& x) const { return cur == x.cur; }
  bool operator!=(const self& x) const { return !(*this == x); }
  bool operator<(const self& x) const {
    return (node == x.node) ? (cur < x.cur) : (node < x.node);
  }
  //使用 set_node 来跳一个缓冲区
  void set_node(map_pointer new_node) {
    node = new_node;
    first = *new_node;
    last = first + difference_type(buffer_size());
  }
};

#ifndef __STL_CLASS_PARTIAL_SPECIALIZATION

#ifndef __STL_NON_TYPE_TMPL_PARAM_BUG

template <class T, class Ref, class Ptr, size_t BufSiz>
inline random_access_iterator_tag
iterator_category(const __deque_iterator<T, Ref, Ptr, BufSiz>&) {
  return random_access_iterator_tag();
}

template <class T, class Ref, class Ptr, size_t BufSiz>
inline T* value_type(const __deque_iterator<T, Ref, Ptr, BufSiz>&) {
  return 0;
}

template <class T, class Ref, class Ptr, size_t BufSiz>
inline ptrdiff_t* distance_type(const __deque_iterator<T, Ref, Ptr, BufSiz>&) {
  return 0;
}

#else /* __STL_NON_TYPE_TMPL_PARAM_BUG */

template <class T, class Ref, class Ptr>
inline random_access_iterator_tag
iterator_category(const __deque_iterator<T, Ref, Ptr>&) {
  return random_access_iterator_tag();
}

template <class T, class Ref, class Ptr>
inline T* value_type(const __deque_iterator<T, Ref, Ptr>&) { return 0; }

template <class T, class Ref, class Ptr>
inline ptrdiff_t* distance_type(const __deque_iterator<T, Ref, Ptr>&) {
  return 0;
}

#endif /* __STL_NON_TYPE_TMPL_PARAM_BUG */

#endif /* __STL_CLASS_PARTIAL_SPECIALIZATION */

// See __deque_buf_size().  The only reason that the default value is 0
//  is as a workaround for bugs in the way that some compilers handle
//  constant expressions.

// deque 类
template <class T, class Alloc = alloc, size_t BufSiz = 0>
class deque {
public:                         // Basic types
  typedef T value_type;
  typedef value_type* pointer;
  typedef const value_type* const_pointer;
  typedef value_type& reference;
  typedef const value_type& const_reference;
  typedef size_t size_type;
  typedef ptrdiff_t difference_type;

public:                         // Iterators
#ifndef __STL_NON_TYPE_TMPL_PARAM_BUG
  typedef __deque_iterator<T, T&, T*, BufSiz>              iterator;
  typedef __deque_iterator<T, const T&, const T&, BufSiz>  const_iterator;
#else /* __STL_NON_TYPE_TMPL_PARAM_BUG */
  typedef __deque_iterator<T, T&, T*>                      iterator;
  typedef __deque_iterator<T, const T&, const T*>          const_iterator;
#endif /* __STL_NON_TYPE_TMPL_PARAM_BUG */

#ifdef __STL_CLASS_PARTIAL_SPECIALIZATION
  typedef reverse_iterator<const_iterator> const_reverse_iterator;
  typedef reverse_iterator<iterator> reverse_iterator;
#else /* __STL_CLASS_PARTIAL_SPECIALIZATION */
  typedef reverse_iterator<const_iterator, value_type, const_reference,
                           difference_type>
          const_reverse_iterator;
  typedef reverse_iterator<iterator, value_type, reference, difference_type>
          reverse_iterator;
#endif /* __STL_CLASS_PARTIAL_SPECIALIZATION */

protected:                      // Internal typedefs
  //元素指针的指针，即指向 map 中元素的指针
  typedef pointer* map_pointer;
  //空间配置器。每次配置一个元素大小
  typedef simple_alloc<value_type, Alloc> data_allocator;
  //空间配置器，每次配置一个指针大小
  typedef simple_alloc<pointer, Alloc> map_allocator;

  static size_type buffer_size() {
    return __deque_buf_size(BufSiz, sizeof(value_type));
  }
  static size_type initial_map_size() { return 8; }

protected:                      // Data members
  iterator start;				//第一缓冲区的第一个元素
  iterator finish;				//最后缓冲区的最后一个元素

  map_pointer map; //指向 map
  size_type map_size; // map 内可容纳多少指针

public:                         // Basic accessors
  iterator begin() { return start; }
  iterator end() { return finish; }
  const_iterator begin() const { return start; }
  const_iterator end() const { return finish; }

  reverse_iterator rbegin() { return reverse_iterator(finish); }
  reverse_iterator rend() { return reverse_iterator(start); }
  const_reverse_iterator rbegin() const {
    return const_reverse_iterator(finish);
  }
  const_reverse_iterator rend() const {
    return const_reverse_iterator(start);
  }

  reference operator[](size_type n) { return start[difference_type(n)]; }
  const_reference operator[](size_type n) const {
    return start[difference_type(n)];
  }

  reference front() { return *start; }
  reference back() {
    //?

下面三行为什么不改为： return *(finish - 1);
	iterator tmp = finish;
    --tmp;
    return *tmp;
  }
  const_reference front() const { return *start; }
  const_reference back() const {
    const_iterator tmp = finish;
    --tmp;
    return *tmp;
  }

  size_type size() const { return finish - start;; }
  size_type max_size() const { return size_type(-1); }
  bool empty() const { return finish == start; }

public:                         // Constructor, destructor.
  deque()
    : start(), finish(), map(0), map_size(0)
  {
    create_map_and_nodes(0);
  }

  deque(const deque& x)
    : start(), finish(), map(0), map_size(0)
  {
    create_map_and_nodes(x.size());
    __STL_TRY {
      uninitialized_copy(x.begin(), x.end(), start);
    }
    __STL_UNWIND(destroy_map_and_nodes());
  }

  deque(size_type n, const value_type& value)
    : start(), finish(), map(0), map_size(0)
  {
    fill_initialize(n, value);
  }

  deque(int n, const value_type& value)
    : start(), finish(), map(0), map_size(0)
  {
    fill_initialize(n, value);
  }

  deque(long n, const value_type& value)
    : start(), finish(), map(0), map_size(0)
  {
    fill_initialize(n, value);
  }

  explicit deque(size_type n)
    : start(), finish(), map(0), map_size(0)
  {
    fill_initialize(n, value_type());
  }

#ifdef __STL_MEMBER_TEMPLATES

  template <class InputIterator>
  deque(InputIterator first, InputIterator last)
    : start(), finish(), map(0), map_size(0)
  {
    range_initialize(first, last, iterator_category(first));
  }

#else /* __STL_MEMBER_TEMPLATES */

  deque(const value_type* first, const value_type* last)
    : start(), finish(), map(0), map_size(0)
  {
    create_map_and_nodes(last - first);
    __STL_TRY {
      uninitialized_copy(first, last, start);
    }
    __STL_UNWIND(destroy_map_and_nodes());
  }

  deque(const_iterator first, const_iterator last)
    : start(), finish(), map(0), map_size(0)
  {
    create_map_and_nodes(last - first);
    __STL_TRY {
      uninitialized_copy(first, last, start);
    }
    __STL_UNWIND(destroy_map_and_nodes());
  }

#endif /* __STL_MEMBER_TEMPLATES */

  ~deque() {
    destroy(start, finish);
    destroy_map_and_nodes();
  }

  deque& operator= (const deque& x) {
    const size_type len = size();
    if (&x != this) {
      if (len >= x.size())
        erase(copy(x.begin(), x.end(), start), finish);
      else {
        const_iterator mid = x.begin() + difference_type(len);
        copy(x.begin(), mid, start);
        insert(finish, mid, x.end());
      }
    }
    return *this;
  }        

  void swap(deque& x) {
    __STD::swap(start, x.start);
    __STD::swap(finish, x.finish);
    __STD::swap(map, x.map);
    __STD::swap(map_size, x.map_size);
  }

public:                         // push_* and pop_*

  void push_back(const value_type& t) {
    //最后缓冲区尚有一个以上的备用空间
    if (finish.cur != finish.last - 1) {
      construct(finish.cur, t);
      ++finish.cur;
    }
	//仅仅剩一个备用空间
    else
      push_back_aux(t);
  }

  void push_front(const value_type& t) {
    //第一缓冲区尚有备用空间
    if (start.cur != start.first) {
      construct(start.cur - 1, t);
      --start.cur;
    }
	//尚有备用空间
    else
      push_front_aux(t);
  }

  void pop_back() {
    //最后缓冲区有一个或很多其它的元素
    if (finish.cur != finish.first) {
      --finish.cur; //指针前移。相当于排除了最后的元素
      destroy(finish.cur); //析构并释放最后的元素
    }
	//最后缓冲区没有不论什么元素
    else
      pop_back_aux();
  }

  void pop_front() {
    //第一缓冲区有一个或很多其它个元素
    if (start.cur != start.last - 1) {
      destroy(start.cur);
      ++start.cur;
    }
	//第一缓冲区且有一个元素
    else
      pop_front_aux();
  }

public:                         // Insert

  iterator insert(iterator position, const value_type& x) {
   //假设插入点是 deque 最前端，交给 push_front 去做
    if (position.cur == start.cur) {
      push_front(x);
      return start;
    }
	//假设插入点是 deque 最后端，交给 push_back 去做
    else if (position.cur == finish.cur) {
      push_back(x);
      iterator tmp = finish;
      --tmp;
      return tmp;
    }
	//其它情况交给 insert_aux 去做
    else {
      return insert_aux(position, x);
    }
  }

  iterator insert(iterator position) { return insert(position, value_type()); }

  void insert(iterator pos, size_type n, const value_type& x); 

  void insert(iterator pos, int n, const value_type& x) {
    insert(pos, (size_type) n, x);
  }
  void insert(iterator pos, long n, const value_type& x) {
    insert(pos, (size_type) n, x);
  }

#ifdef __STL_MEMBER_TEMPLATES  

  template <class InputIterator>
  void insert(iterator pos, InputIterator first, InputIterator last) {
    insert(pos, first, last, iterator_category(first));
  }

#else /* __STL_MEMBER_TEMPLATES */

  void insert(iterator pos, const value_type* first, const value_type* last);
  void insert(iterator pos, const_iterator first, const_iterator last);

#endif /* __STL_MEMBER_TEMPLATES */

  void resize(size_type new_size, const value_type& x) {
    const size_type len = size();
    if (new_size < len)
      erase(start + new_size, finish);
    else
      insert(finish, new_size - len, x);
  }

  void resize(size_type new_size) { resize(new_size, value_type()); }

public:                         // Erase
  //清除 pos 所指的元素
  iterator erase(iterator pos) {
    iterator next = pos;
    ++next;
    difference_type index = pos - start; // 清除点前的元素个数
    if (index < (size() >> 1)) { // 假设清除点之前的元素比較少，则移动清除点之前的元素
      copy_backward(start, pos, next);
      pop_front();
    }
    else { //假设清除点之后的元素比較少，则移动清除点之后的元素
      copy(next, finish, pos);
      pop_back();
    }
    return start + index;
  }

  iterator erase(iterator first, iterator last);
  void clear(); 

protected:                        // Internal construction/destruction

  void create_map_and_nodes(size_type num_elements);
  void destroy_map_and_nodes();
  void fill_initialize(size_type n, const value_type& value);

#ifdef __STL_MEMBER_TEMPLATES  

  template <class InputIterator>
  void range_initialize(InputIterator first, InputIterator last,
                        input_iterator_tag);

  template <class ForwardIterator>
  void range_initialize(ForwardIterator first, ForwardIterator last,
                        forward_iterator_tag);

#endif /* __STL_MEMBER_TEMPLATES */

protected:                        // Internal push_* and pop_*

  void push_back_aux(const value_type& t);
  void push_front_aux(const value_type& t);
  void pop_back_aux();
  void pop_front_aux();

protected:                        // Internal insert functions

#ifdef __STL_MEMBER_TEMPLATES  

  template <class InputIterator>
  void insert(iterator pos, InputIterator first, InputIterator last,
              input_iterator_tag);

  template <class ForwardIterator>
  void insert(iterator pos, ForwardIterator first, ForwardIterator last,
              forward_iterator_tag);

#endif /* __STL_MEMBER_TEMPLATES */

  iterator insert_aux(iterator pos, const value_type& x);
  void insert_aux(iterator pos, size_type n, const value_type& x);

#ifdef __STL_MEMBER_TEMPLATES  

  template <class ForwardIterator>
  void insert_aux(iterator pos, ForwardIterator first, ForwardIterator last,
                  size_type n);

#else /* __STL_MEMBER_TEMPLATES */

  void insert_aux(iterator pos,
                  const value_type* first, const value_type* last,
                  size_type n);

  void insert_aux(iterator pos, const_iterator first, const_iterator last,
                  size_type n);

#endif /* __STL_MEMBER_TEMPLATES */

  iterator reserve_elements_at_front(size_type n) {
    size_type vacancies = start.cur - start.first;
    if (n > vacancies)
      new_elements_at_front(n - vacancies);
    return start - difference_type(n);
  }

  iterator reserve_elements_at_back(size_type n) {
    size_type vacancies = (finish.last - finish.cur) - 1;
    if (n > vacancies)
      new_elements_at_back(n - vacancies);
    return finish + difference_type(n);
  }

  void new_elements_at_front(size_type new_elements);
  void new_elements_at_back(size_type new_elements);

  void destroy_nodes_at_front(iterator before_start);
  void destroy_nodes_at_back(iterator after_finish);

protected:                      // Allocation of map and nodes

  // Makes sure the map has space for new nodes.  Does not actually
  //  add the nodes.  Can invalidate map pointers.  (And consequently,
  //  deque iterators.)

  void reserve_map_at_back (size_type nodes_to_add = 1) {
    if (nodes_to_add + 1 > map_size - (finish.node - map))
      reallocate_map(nodes_to_add, false);
  }

  void reserve_map_at_front (size_type nodes_to_add = 1) {
    if (nodes_to_add > start.node - map)
      reallocate_map(nodes_to_add, true);
  }

  void reallocate_map(size_type nodes_to_add, bool add_at_front);

  pointer allocate_node() { return data_allocator::allocate(buffer_size()); }
  void deallocate_node(pointer n) {
    data_allocator::deallocate(n, buffer_size());
  }

#ifdef __STL_NON_TYPE_TMPL_PARAM_BUG
public:
  bool operator==(const deque<T, Alloc, 0>& x) const {
    return size() == x.size() && equal(begin(), end(), x.begin());
  }
  bool operator!=(const deque<T, Alloc, 0>& x) const {
    return size() != x.size() || !equal(begin(), end(), x.begin());
  }
  bool operator<(const deque<T, Alloc, 0>& x) const {
    return lexicographical_compare(begin(), end(), x.begin(), x.end());
  }
#endif /* __STL_NON_TYPE_TMPL_PARAM_BUG */
};

// Non-inline member functions

template <class T, class Alloc, size_t BufSize>
void deque<T, Alloc, BufSize>::insert(iterator pos,
                                      size_type n, const value_type& x) {
  if (pos.cur == start.cur) {
    iterator new_start = reserve_elements_at_front(n);
    uninitialized_fill(new_start, start, x);
    start = new_start;
  }
  else if (pos.cur == finish.cur) {
    iterator new_finish = reserve_elements_at_back(n);
    uninitialized_fill(finish, new_finish, x);
    finish = new_finish;
  }
  else
    insert_aux(pos, n, x);
}

#ifndef __STL_MEMBER_TEMPLATES  

template <class T, class Alloc, size_t BufSize>
void deque<T, Alloc, BufSize>::insert(iterator pos,
                                      const value_type* first,
                                      const value_type* last) {
  size_type n = last - first;
  if (pos.cur == start.cur) {
    iterator new_start = reserve_elements_at_front(n);
    __STL_TRY {
      uninitialized_copy(first, last, new_start);
      start = new_start;
    }
    __STL_UNWIND(destroy_nodes_at_front(new_start));
  }
  else if (pos.cur == finish.cur) {
    iterator new_finish = reserve_elements_at_back(n);
    __STL_TRY {
      uninitialized_copy(first, last, finish);
      finish = new_finish;
    }
    __STL_UNWIND(destroy_nodes_at_back(new_finish));
  }
  else
    insert_aux(pos, first, last, n);
}

template <class T, class Alloc, size_t BufSize>
void deque<T, Alloc, BufSize>::insert(iterator pos,
                                      const_iterator first,
                                      const_iterator last)
{
  size_type n = last - first;
  if (pos.cur == start.cur) {
    iterator new_start = reserve_elements_at_front(n);
    __STL_TRY {
      uninitialized_copy(first, last, new_start);
      start = new_start;
    }
    __STL_UNWIND(destroy_nodes_at_front(new_start));
  }
  else if (pos.cur == finish.cur) {
    iterator new_finish = reserve_elements_at_back(n);
    __STL_TRY {
      uninitialized_copy(first, last, finish);
      finish = new_finish;
    }
    __STL_UNWIND(destroy_nodes_at_back(new_finish));
  }
  else
    insert_aux(pos, first, last, n);
}

#endif /* __STL_MEMBER_TEMPLATES */

template <class T, class Alloc, size_t BufSize>
deque<T, Alloc, BufSize>::iterator
//清除[first, last)区间内的全部元素
deque<T, Alloc, BufSize>::erase(iterator first, iterator last) {
  //假设清除区间就是整个 deque ，直接调用 clear() 就可以
  if (first == start && last == finish) {
    clear();
    return finish;
  }
  else {
    difference_type n = last - first;
    difference_type elems_before = first - start;
	//假设清除区间前面的元素较少，向后移动前方元素(覆盖清除区间)。然后析构冗余元素
    if (elems_before < (size() - n) / 2) {
      copy_backward(start, first, last);
      iterator new_start = start + n;
      destroy(start, new_start);
      for (map_pointer cur = start.node; cur < new_start.node; ++cur)
        data_allocator::deallocate(*cur, buffer_size());
      start = new_start;
    }
	//假设清除区间后面的元素较少。向前移动后方元素，然后析构冗余元素
    else {
      copy(last, finish, first);
      iterator new_finish = finish - n;
      destroy(new_finish, finish);
      for (map_pointer cur = new_finish.node + 1; cur <= finish.node; ++cur)
        data_allocator::deallocate(*cur, buffer_size());
      finish = new_finish;
    }
    return start + elems_before;
  }
}

//清除整个 deque ，须要保有一个缓冲区。

template <class T, class Alloc, size_t BufSize>
void deque<T, Alloc, BufSize>::clear() {
  //针对头尾以外的每一个缓冲区。析构全部元素并释放缓冲区空间
  for (map_pointer node = start.node + 1; node < finish.node; ++node) {
    destroy(*node, *node + buffer_size());
    data_allocator::deallocate(*node, buffer_size());
  }
  //还剩头尾两个缓冲区
  if (start.node != finish.node) {
    destroy(start.cur, start.last);
    destroy(finish.first, finish.cur);
	//仅仅释放尾部缓冲区的空间，保留头缓冲区
    data_allocator::deallocate(finish.first, buffer_size());
  }
  //仅仅剩一个缓冲区
  else
    //不释放唯一的缓冲区空间
    destroy(start.cur, finish.cur);

  finish = start;
}
//产生并安排好 deque 的结构
template <class T, class Alloc, size_t BufSize>
void deque<T, Alloc, BufSize>::create_map_and_nodes(size_type num_elements) {
  //须要的节点数 = (元素个数/每一个缓冲区可容纳的元素个数) + 1
  //假设刚好整除。会多配一个节点
  size_type num_nodes = num_elements / buffer_size() + 1;
  // initial_map_size 函数返回 8 ，所以这里是取 8 和 "所需节点数加2(前后预留一个。扩充时可用)" 的最大值
  map_size = max(initial_map_size(), num_nodes + 2);
  //配置出一个"具有 map_size 个节点"的 map
  map = map_allocator::allocate(map_size);

  //令 nstart 和 nfinish 指向 map 所拥有之全部节点的最中央区段
  map_pointer nstart = map + (map_size - num_nodes) / 2;
  map_pointer nfinish = nstart + num_nodes - 1;

  map_pointer cur;
  __STL_TRY {
    //为 map 内的每一个现用节点配置缓冲区。

全部缓冲区加起来就是 deque 的可用空间(最后一个缓冲区可能留有一些余裕)
    for (cur = nstart; cur <= nfinish; ++cur)
      *cur = allocate_node();
  }
#     ifdef  __STL_USE_EXCEPTIONS
  catch(...) {
    for (map_pointer n = nstart; n < cur; ++n)
      deallocate_node(*n);
    map_allocator::deallocate(map, map_size);
    throw;
  }
#     endif /* __STL_USE_EXCEPTIONS */
  //为 deque 内的两个迭代器 start 和 end 设定正确内容
  start.set_node(nstart);
  finish.set_node(nfinish);
  start.cur = start.first;
  finish.cur = finish.first + num_elements % buffer_size();
}

// This is only used as a cleanup function in catch clauses.
template <class T, class Alloc, size_t BufSize>
void deque<T, Alloc, BufSize>::destroy_map_and_nodes() {
  for (map_pointer cur = start.node; cur <= finish.node; ++cur)
    deallocate_node(*cur);
  map_allocator::deallocate(map, map_size);
}

//负责产生并安排好 deque 的结构，并元素的初值设定妥当
template <class T, class Alloc, size_t BufSize>
void deque<T, Alloc, BufSize>::fill_initialize(size_type n,
                                               const value_type& value) {
  create_map_and_nodes(n);//把 deque 的结构都产生并安排好
  map_pointer cur;
  __STL_TRY {
    //为每一个节点的缓冲区设定初值
    for (cur = start.node; cur < finish.node; ++cur)
      uninitialized_fill(*cur, *cur + buffer_size(), value);
    //最后一个节点的设定稍有不同(由于尾端可能有备用空间。不必设初值)
	uninitialized_fill(finish.first, finish.cur, value);
  }
#       ifdef __STL_USE_EXCEPTIONS
  catch(...) {
    for (map_pointer n = start.node; n < cur; ++n)
      destroy(*n, *n + buffer_size());
    destroy_map_and_nodes();
    throw;
  }
#       endif /* __STL_USE_EXCEPTIONS */
}

#ifdef __STL_MEMBER_TEMPLATES  

template <class T, class Alloc, size_t BufSize>
template <class InputIterator>
void deque<T, Alloc, BufSize>::range_initialize(InputIterator first,
                                                InputIterator last,
                                                input_iterator_tag) {
  create_map_and_nodes(0);
  for ( ; first != last; ++first)
    push_back(*first);
}

template <class T, class Alloc, size_t BufSize>
template <class ForwardIterator>
void deque<T, Alloc, BufSize>::range_initialize(ForwardIterator first,
                                                ForwardIterator last,
                                                forward_iterator_tag) {
  size_type n = 0;
  distance(first, last, n);
  create_map_and_nodes(n);
  __STL_TRY {
    uninitialized_copy(first, last, start);
  }
  __STL_UNWIND(destroy_map_and_nodes());
}

#endif /* __STL_MEMBER_TEMPLATES */

// 仅仅有当 finish.cur == finish.last - 1 时才会调用，即仅仅剩一个备用空间
template <class T, class Alloc, size_t BufSize>
void deque<T, Alloc, BufSize>::push_back_aux(const value_type& t) {
  value_type t_copy = t;
  reserve_map_at_back();
  //配置一个新缓冲区
  *(finish.node + 1) = allocate_node();
  __STL_TRY {
    construct(finish.cur, t_copy); //设置元素值
    finish.set_node(finish.node + 1); //改变 finish， 令其指向新节点
    finish.cur = finish.first; //设定 finish 的状态
  }
  __STL_UNWIND(deallocate_node(*(finish.node + 1)));
}

// 仅仅有当 start.cur == start.first 才会被调用。即第一个缓冲区尚有备用空间可用了
//--> 为什么 push_back 的时候是仅仅有一个备用空间时调用。而 push_front 是没有备用空间时调用 ？？
template <class T, class Alloc, size_t BufSize>
void deque<T, Alloc, BufSize>::push_front_aux(const value_type& t) {
  value_type t_copy = t;
  reserve_map_at_front();
  *(start.node - 1) = allocate_node();
  __STL_TRY {
    start.set_node(start.node - 1);
    start.cur = start.last - 1;
    construct(start.cur, t_copy);
  }
#     ifdef __STL_USE_EXCEPTIONS
  catch(...) {
    start.set_node(start.node + 1);
    start.cur = start.first;
    deallocate_node(*(start.node - 1));
    throw;
  }
#     endif /* __STL_USE_EXCEPTIONS */
} 

// 仅仅有当 finish.cur == finish.first 时才会调用
template <class T, class Alloc, size_t BufSize>
void deque<T, Alloc, BufSize>:: pop_back_aux() {
  deallocate_node(finish.first); //释放最后一个缓冲区
  finish.set_node(finish.node - 1); //调整 finish 的状态，使指向上一个缓冲区的最后一个元素
  finish.cur = finish.last - 1;
  destroy(finish.cur); //将该元素析构
}

//仅仅有当 start.cur == start.last - 1 时才会调用
template <class T, class Alloc, size_t BufSize>
void deque<T, Alloc, BufSize>::pop_front_aux() {
  destroy(start.cur); //将第一缓冲区的第一个元素析构
  deallocate_node(start.first); //释放第一缓冲区
  start.set_node(start.node + 1); //调整 start 的状态，使指向下一个缓冲区的第一个元素
  start.cur = start.first;
}      

#ifdef __STL_MEMBER_TEMPLATES  

template <class T, class Alloc, size_t BufSize>
template <class InputIterator>
void deque<T, Alloc, BufSize>::insert(iterator pos,
                                      InputIterator first, InputIterator last,
                                      input_iterator_tag) {
  copy(first, last, inserter(*this, pos));
}

template <class T, class Alloc, size_t BufSize>
template <class ForwardIterator>
void deque<T, Alloc, BufSize>::insert(iterator pos,
                                      ForwardIterator first,
                                      ForwardIterator last,
                                      forward_iterator_tag) {
  size_type n = 0;
  distance(first, last, n);
  if (pos.cur == start.cur) {
    iterator new_start = reserve_elements_at_front(n);
    __STL_TRY {
      uninitialized_copy(first, last, new_start);
      start = new_start;
    }
    __STL_UNWIND(destroy_nodes_at_front(new_start));
  }
  else if (pos.cur == finish.cur) {
    iterator new_finish = reserve_elements_at_back(n);
    __STL_TRY {
      uninitialized_copy(first, last, finish);
      finish = new_finish;
    }
    __STL_UNWIND(destroy_nodes_at_back(new_finish));
  }
  else
    insert_aux(pos, first, last, n);
}

#endif /* __STL_MEMBER_TEMPLATES */

template <class T, class Alloc, size_t BufSize>
typename deque<T, Alloc, BufSize>::iterator
deque<T, Alloc, BufSize>::insert_aux(iterator pos, const value_type& x) {
  difference_type index = pos - start;
  value_type x_copy = x;
  //假设插入点之前的元素个数比較少。在最前端增加与第一个元素同值的元素，然后进行元素移动
  if (index < size() / 2) {
    push_front(front());
    iterator front1 = start;
    ++front1;
    iterator front2 = front1;
    ++front2;
    pos = start + index;
    iterator pos1 = pos;
    ++pos1;
    copy(front2, pos1, front1);
  }

  //假设插入点之后的元素个数比較少，在最后端增加与最后一个元素同值的元素。然后进行元素移动
  else {
    push_back(back());
    iterator back1 = finish;
    --back1;
    iterator back2 = back1;
    --back2;
    pos = start + index;
    copy_backward(pos, back2, back1);
  }
  //在插入点上设定新值
  *pos = x_copy;
  return pos;
}

template <class T, class Alloc, size_t BufSize>
void deque<T, Alloc, BufSize>::insert_aux(iterator pos,
                                          size_type n, const value_type& x) {
  const difference_type elems_before = pos - start;
  size_type length = size();
  value_type x_copy = x;
  if (elems_before < length / 2) {
    iterator new_start = reserve_elements_at_front(n);
    iterator old_start = start;
    pos = start + elems_before;
    __STL_TRY {
      if (elems_before >= difference_type(n)) {
        iterator start_n = start + difference_type(n);
        uninitialized_copy(start, start_n, new_start);
        start = new_start;
        copy(start_n, pos, old_start);
        fill(pos - difference_type(n), pos, x_copy);
      }
      else {
        __uninitialized_copy_fill(start, pos, new_start, start, x_copy);
        start = new_start;
        fill(old_start, pos, x_copy);
      }
    }
    __STL_UNWIND(destroy_nodes_at_front(new_start));
  }
  else {
    iterator new_finish = reserve_elements_at_back(n);
    iterator old_finish = finish;
    const difference_type elems_after = difference_type(length) - elems_before;
    pos = finish - elems_after;
    __STL_TRY {
      if (elems_after > difference_type(n)) {
        iterator finish_n = finish - difference_type(n);
        uninitialized_copy(finish_n, finish, finish);
        finish = new_finish;
        copy_backward(pos, finish_n, old_finish);
        fill(pos, pos + difference_type(n), x_copy);
      }
      else {
        __uninitialized_fill_copy(finish, pos + difference_type(n),
                                  x_copy,
                                  pos, finish);
        finish = new_finish;
        fill(pos, old_finish, x_copy);
      }
    }
    __STL_UNWIND(destroy_nodes_at_back(new_finish));
  }
}

#ifdef __STL_MEMBER_TEMPLATES  

template <class T, class Alloc, size_t BufSize>
template <class ForwardIterator>
void deque<T, Alloc, BufSize>::insert_aux(iterator pos,
                                          ForwardIterator first,
                                          ForwardIterator last,
                                          size_type n)
{
  const difference_type elems_before = pos - start;
  size_type length = size();
  if (elems_before < length / 2) {
    iterator new_start = reserve_elements_at_front(n);
    iterator old_start = start;
    pos = start + elems_before;
    __STL_TRY {
      if (elems_before >= difference_type(n)) {
        iterator start_n = start + difference_type(n);
        uninitialized_copy(start, start_n, new_start);
        start = new_start;
        copy(start_n, pos, old_start);
        copy(first, last, pos - difference_type(n));
      }
      else {
        ForwardIterator mid = first;
        advance(mid, difference_type(n) - elems_before);
        __uninitialized_copy_copy(start, pos, first, mid, new_start);
        start = new_start;
        copy(mid, last, old_start);
      }
    }
    __STL_UNWIND(destroy_nodes_at_front(new_start));
  }
  else {
    iterator new_finish = reserve_elements_at_back(n);
    iterator old_finish = finish;
    const difference_type elems_after = difference_type(length) - elems_before;
    pos = finish - elems_after;
    __STL_TRY {
      if (elems_after > difference_type(n)) {
        iterator finish_n = finish - difference_type(n);
        uninitialized_copy(finish_n, finish, finish);
        finish = new_finish;
        copy_backward(pos, finish_n, old_finish);
        copy(first, last, pos);
      }
      else {
        ForwardIterator mid = first;
        advance(mid, elems_after);
        __uninitialized_copy_copy(mid, last, pos, finish, finish);
        finish = new_finish;
        copy(first, mid, pos);
      }
    }
    __STL_UNWIND(destroy_nodes_at_back(new_finish));
  }
}

#else /* __STL_MEMBER_TEMPLATES */

template <class T, class Alloc, size_t BufSize>
void deque<T, Alloc, BufSize>::insert_aux(iterator pos,
                                          const value_type* first,
                                          const value_type* last,
                                          size_type n)
{
  const difference_type elems_before = pos - start;
  size_type length = size();
  if (elems_before < length / 2) {
    iterator new_start = reserve_elements_at_front(n);
    iterator old_start = start;
    pos = start + elems_before;
    __STL_TRY {
      if (elems_before >= difference_type(n)) {
        iterator start_n = start + difference_type(n);
        uninitialized_copy(start, start_n, new_start);
        start = new_start;
        copy(start_n, pos, old_start);
        copy(first, last, pos - difference_type(n));
      }
      else {
        const value_type* mid = first + (difference_type(n) - elems_before);
        __uninitialized_copy_copy(start, pos, first, mid, new_start);
        start = new_start;
        copy(mid, last, old_start);
      }
    }
    __STL_UNWIND(destroy_nodes_at_front(new_start));
  }
  else {
    iterator new_finish = reserve_elements_at_back(n);
    iterator old_finish = finish;
    const difference_type elems_after = difference_type(length) - elems_before;
    pos = finish - elems_after;
    __STL_TRY {
      if (elems_after > difference_type(n)) {
        iterator finish_n = finish - difference_type(n);
        uninitialized_copy(finish_n, finish, finish);
        finish = new_finish;
        copy_backward(pos, finish_n, old_finish);
        copy(first, last, pos);
      }
      else {
        const value_type* mid = first + elems_after;
        __uninitialized_copy_copy(mid, last, pos, finish, finish);
        finish = new_finish;
        copy(first, mid, pos);
      }
    }
    __STL_UNWIND(destroy_nodes_at_back(new_finish));
  }
}

template <class T, class Alloc, size_t BufSize>
void deque<T, Alloc, BufSize>::insert_aux(iterator pos,
                                          const_iterator first,
                                          const_iterator last,
                                          size_type n)
{
  const difference_type elems_before = pos - start;
  size_type length = size();
  if (elems_before < length / 2) {
    iterator new_start = reserve_elements_at_front(n);
    iterator old_start = start;
    pos = start + elems_before;
    __STL_TRY {
      if (elems_before >= n) {
        iterator start_n = start + n;
        uninitialized_copy(start, start_n, new_start);
        start = new_start;
        copy(start_n, pos, old_start);
        copy(first, last, pos - difference_type(n));
      }
      else {
        const_iterator mid = first + (n - elems_before);
        __uninitialized_copy_copy(start, pos, first, mid, new_start);
        start = new_start;
        copy(mid, last, old_start);
      }
    }
    __STL_UNWIND(destroy_nodes_at_front(new_start));
  }
  else {
    iterator new_finish = reserve_elements_at_back(n);
    iterator old_finish = finish;
    const difference_type elems_after = length - elems_before;
    pos = finish - elems_after;
    __STL_TRY {
      if (elems_after > n) {
        iterator finish_n = finish - difference_type(n);
        uninitialized_copy(finish_n, finish, finish);
        finish = new_finish;
        copy_backward(pos, finish_n, old_finish);
        copy(first, last, pos);
      }
      else {
        const_iterator mid = first + elems_after;
        __uninitialized_copy_copy(mid, last, pos, finish, finish);
        finish = new_finish;
        copy(first, mid, pos);
      }
    }
    __STL_UNWIND(destroy_nodes_at_back(new_finish));
  }
}

#endif /* __STL_MEMBER_TEMPLATES */

template <class T, class Alloc, size_t BufSize>
void deque<T, Alloc, BufSize>::new_elements_at_front(size_type new_elements) {
  size_type new_nodes = (new_elements + buffer_size() - 1) / buffer_size();
  reserve_map_at_front(new_nodes);
  size_type i;
  __STL_TRY {
    for (i = 1; i <= new_nodes; ++i)
      *(start.node - i) = allocate_node();
  }
#       ifdef __STL_USE_EXCEPTIONS
  catch(...) {
    for (size_type j = 1; j < i; ++j)
      deallocate_node(*(start.node - j));
    throw;
  }
#       endif /* __STL_USE_EXCEPTIONS */
}

template <class T, class Alloc, size_t BufSize>
void deque<T, Alloc, BufSize>::new_elements_at_back(size_type new_elements) {
  size_type new_nodes = (new_elements + buffer_size() - 1) / buffer_size();
  reserve_map_at_back(new_nodes);
  size_type i;
  __STL_TRY {
    for (i = 1; i <= new_nodes; ++i)
      *(finish.node + i) = allocate_node();
  }
#       ifdef __STL_USE_EXCEPTIONS
  catch(...) {
    for (size_type j = 1; j < i; ++j)
      deallocate_node(*(finish.node + j));
    throw;
  }
#       endif /* __STL_USE_EXCEPTIONS */
}

template <class T, class Alloc, size_t BufSize>
void deque<T, Alloc, BufSize>::destroy_nodes_at_front(iterator before_start) {
  for (map_pointer n = before_start.node; n < start.node; ++n)
    deallocate_node(*n);
}

template <class T, class Alloc, size_t BufSize>
void deque<T, Alloc, BufSize>::destroy_nodes_at_back(iterator after_finish) {
  for (map_pointer n = after_finish.node; n > finish.node; --n)
    deallocate_node(*n);
}

//重换一个 map (配置更大的，拷贝原来的，释放原来的)
template <class T, class Alloc, size_t BufSize>
void deque<T, Alloc, BufSize>::reallocate_map(size_type nodes_to_add,
                                              bool add_at_front) {
  size_type old_num_nodes = finish.node - start.node + 1;//旧节点数
  size_type new_num_nodes = old_num_nodes + nodes_to_add;//新节点数

  map_pointer new_nstart;
  //当前 map 的大小大于新节点数的两倍的情况
  //即当前 map 足够大，则调整节点区间让它落在 map 的中间
  if (map_size > 2 * new_num_nodes) {
    new_nstart = map + (map_size - new_num_nodes) / 2
                     + (add_at_front ? nodes_to_add : 0);
    if (new_nstart < start.node)
      copy(start.node, finish.node + 1, new_nstart);
    else
      copy_backward(start.node, finish.node + 1, new_nstart + old_num_nodes);
  }
  //否则，配置一块新的空间
  else {
    size_type new_map_size = map_size + max(map_size, nodes_to_add) + 2;

	//配置一块新的空间
    map_pointer new_map = map_allocator::allocate(new_map_size);
    new_nstart = new_map + (new_map_size - new_num_nodes) / 2
                         + (add_at_front ? nodes_to_add : 0);
    //拷贝原 map
	copy(start.node, finish.node + 1, new_nstart);
    //释放原 map
	map_allocator::deallocate(map, map_size);
	//设定新 map 的起始地址和大小
    map = new_map;
    map_size = new_map_size;
  }
  //又一次设定迭代器 start 和 finish
  start.set_node(new_nstart);
  finish.set_node(new_nstart + old_num_nodes - 1);
}

// Nonmember functions.

#ifndef __STL_NON_TYPE_TMPL_PARAM_BUG

template <class T, class Alloc, size_t BufSiz>
bool operator==(const deque<T, Alloc, BufSiz>& x,
                const deque<T, Alloc, BufSiz>& y) {
  return x.size() == y.size() && equal(x.begin(), x.end(), y.begin());
}

template <class T, class Alloc, size_t BufSiz>
bool operator<(const deque<T, Alloc, BufSiz>& x,
               const deque<T, Alloc, BufSiz>& y) {
  return lexicographical_compare(x.begin(), x.end(), y.begin(), y.end());
}

#endif /* __STL_NON_TYPE_TMPL_PARAM_BUG */

#if defined(__STL_FUNCTION_TMPL_PARTIAL_ORDER) && \
    !defined(__STL_NON_TYPE_TMPL_PARAM_BUG)

template <class T, class Alloc, size_t BufSiz>
inline void swap(deque<T, Alloc, BufSiz>& x, deque<T, Alloc, BufSiz>& y) {
  x.swap(y);
}

#endif

#if defined(__sgi) && !defined(__GNUC__) && (_MIPS_SIM != _MIPS_SIM_ABI32)
#pragma reset woff 1174
#endif

__STL_END_NAMESPACE 

#endif /* __SGI_STL_INTERNAL_DEQUE_H */

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