STL源码剖析——序列容器之deque

短命女 2022-08-12 06:28 189阅读 0赞

## 前言 ##

deque是一种双向开口的分段连续线性空间，可以在头尾端进行元素的插入和删除。deque与vector最大的差异就是：第一是deque允许于常数时间内对头端进行插入或删除元素；第二是deque是分段连续线性空间，随时可以增加一段新的空间；deque不像vector那样，vector当内存不够时，需重新分配/复制数据/释放原始空间；不过deque的迭代器设置比vector复杂，因为迭代器不能使用普通指针，因此尽量使用vector； 当对deque的元素进行排序时，为了提高效率，首先把deque数据复制到vector，利用vector的排序算法(利用STL的sort算法)，排序之后再次复制回deque；本文所列的源码出自SGI STL中的文件<stl\_deque.h>，对于deque容器类的详细信息也可以查看[《deque容器库》][deque]和[《][Link 1][MSDN][Link 1][的][Link 1][deque][Link 1][类》][Link 1]

## deque容器 ##

### deque中控器 ###

由于deque是分段连续线性空间的，为了用户方便操作，所以它对外的接口类似于连续空间。为了管理这些分段空间deque容器引入了一种中控器map，map是一块连续的空间，其中每个元素是指向缓冲区的指针，缓冲区才是deque存储数据的主体。下面给出map的结构；

_Tp** _M_map;
      size_t _M_map_size;

![SouthEast][]

### deque的迭代器 ###

deque是分段连续的线性空间，则普通指针不能作为deque的迭代器。迭代器设计时必须能够进行 operator++ 或 operator-- 操作，为了能够是用户随机访问容器，则必须对操作符进行重载。  
**deque****迭代器的功能**：

1.  必须知道缓冲区的位置
2.  能够判断是否处于其所在缓冲区的边界
3.  能够知道其所在缓冲区当前所指位置的元素

迭代器的数据结构如下：

struct _Deque_iterator {
    	...
       //以下是迭代器设计的关键，访问容器的节点
      _Tp* _M_cur;//指向缓冲区当前的元素
      _Tp* _M_first;//指向缓冲区的头(起始地址)
      _Tp* _M_last;//指向缓冲区的尾(结束地址)
      _Map_pointer _M_node;//指向中控器的相应节点
      ...
    };

为了实现能够随机访问，deque的中控器、缓冲区和迭代器之间的相互关系如下图所示：

![SouthEast 1][]

以下是对迭代器源码的剖析：

//*	deque是分段连续线性空间，为了能够像连续线性空间那样访问数据，
    //*	deque采用了一种中控方法map,map是块连续的空间，其每个元素都是一个指针，
    //*	指向一块缓冲区，实质上map是T**；
    //***************************************************************
    
    // Note: this function is simply a kludge to work around several compilers'
    //  bugs in handling constant expressions.
    //这个函数是方便不同编译器处理常量表达式的bug
    inline size_t __deque_buf_size(size_t __size) {
      return __size < 512 ? size_t(512 / __size) : size_t(1);
    }
    
    //deque迭代器的设计
    //*deque是分段连续的线性空间，迭代器设计时必须能够进行operator++或operator--操作
    //*	迭代器的功能：
    //*	1、必须知道缓冲区的位置
    //*	2、能够判断是否处于其所在缓冲区的边界
    //*	3、能够知道其所在缓冲区当前所指位置的元素
    //********************************************
    template <class _Tp, class _Ref, class _Ptr>
    struct _Deque_iterator {
      typedef _Deque_iterator<_Tp, _Tp&, _Tp*>             iterator;
      typedef _Deque_iterator<_Tp, const _Tp&, const _Tp*> const_iterator;
      static size_t _S_buffer_size() { return __deque_buf_size(sizeof(_Tp)); }
    
      typedef random_access_iterator_tag iterator_category;
      typedef _Tp value_type;
      typedef _Ptr pointer;
      typedef _Ref reference;
      typedef size_t size_type;
      typedef ptrdiff_t difference_type;
      typedef _Tp** _Map_pointer;
    
      typedef _Deque_iterator _Self;
    
      //以下是迭代器设计的关键，访问容器的节点
      _Tp* _M_cur;//指向缓冲区当前的元素
      _Tp* _M_first;//指向缓冲区的头(起始地址)
      _Tp* _M_last;//指向缓冲区的尾(结束地址)
      _Map_pointer _M_node;//指向中控器的相应节点
    
      _Deque_iterator(_Tp* __x, _Map_pointer __y) 
        : _M_cur(__x), _M_first(*__y),
          _M_last(*__y + _S_buffer_size()), _M_node(__y) {}
      _Deque_iterator() : _M_cur(0), _M_first(0), _M_last(0), _M_node(0) {}
      _Deque_iterator(const iterator& __x)
        : _M_cur(__x._M_cur), _M_first(__x._M_first), 
          _M_last(__x._M_last), _M_node(__x._M_node) {}
    
      //****************************************************************************
      //*********************以下是迭代器_Deque_iterator的操作**********************
      //*	这些操作符的重载方便我们访问容器的内容
      //*	也是让deque从接口看来是维护连续线性空间的关键
      //****************************************************************************
      reference operator*() const { return *_M_cur; }//解除引用,返回当前元素
    #ifndef __SGI_STL_NO_ARROW_OPERATOR
      pointer operator->() const { return _M_cur; }
    #endif /* __SGI_STL_NO_ARROW_OPERATOR */
    
      //返回两个迭代器之间的距离
      difference_type operator-(const _Self& __x) const {
        return difference_type(_S_buffer_size()) * (_M_node - __x._M_node - 1) +
          (_M_cur - _M_first) + (__x._M_last - __x._M_cur);
      }
    
      //前缀自增++操作符重载
      _Self& operator++() {
        ++_M_cur;					//普通自增操作，移至下一个元素
        if (_M_cur == _M_last) {   //若已达到缓冲区的尾部
          _M_set_node(_M_node + 1);//切换至下一缓冲区(节点)
          _M_cur = _M_first;	  //的第一个元素
        }
        return *this;
      }
      //后缀自增++操作符重载
      //返回当前迭代器的一个副本
      _Self operator++(int)  {
        _Self __tmp = *this;//定义当前迭代器的一个副本
        ++*this;//这里前缀++不是普通的++操作，是上一步骤已经重载过的前缀++
        return __tmp;
      }
    
      //前缀自减--操作符重载
      //基本思想类似于前缀自增操作
      _Self& operator--() {
        if (_M_cur == _M_first) {  //若是当前缓冲区的第一个元素
          _M_set_node(_M_node - 1);//切换到上一个缓冲区
          _M_cur = _M_last;		  //的尾部(即最后一个元素的下一个位置)
        }
        --_M_cur;//普通的自减操作，移至前一个元素
        return *this;
      }
      //后缀自减--操作符重载
      //返回当前迭代器的副本
      _Self operator--(int) {
        _Self __tmp = *this;//定义一个副本
        --*this;			//迭代器自减操作
        return __tmp;
      }
    
      //以下实现随机存取，迭代器可以直接跳跃n个距离
      //将迭代器前移n个距离，当n负值时就为下面的operator-=操作
      _Self& operator+=(difference_type __n)
      {
        difference_type __offset = __n + (_M_cur - _M_first);//定义一个中间变量
        if (__offset >= 0 && __offset < difference_type(_S_buffer_size()))
    		//若前移n个距离后，目标依然在同一个缓冲区
    		//则直接前移n个距离
          _M_cur += __n;
        else {
    		//若前移n个距离后，目标超出该缓冲区范围
    		//__offset / difference_type(_S_buffer_size())计算向后移动多少个缓冲区
    		//-difference_type((-__offset - 1) / _S_buffer_size()) - 1计算向前移动多少个缓冲区
          difference_type __node_offset =
            __offset > 0 ? __offset / difference_type(_S_buffer_size())
                       : -difference_type((-__offset - 1) / _S_buffer_size()) - 1;
    	  //调整到正确的缓冲区
          _M_set_node(_M_node + __node_offset);
    	  //切换至正确的元素
          _M_cur = _M_first + 
            (__offset - __node_offset * difference_type(_S_buffer_size()));
        }
        return *this;
      }
    
      //操作符+重载
      //返回操作之后的副本
      _Self operator+(difference_type __n) const
      {
        _Self __tmp = *this;
    	//调用operator+=操作
        return __tmp += __n;
      }
    
      //利用operator+=操作实现
      _Self& operator-=(difference_type __n) { return *this += -__n; }
     
      _Self operator-(difference_type __n) const {
        _Self __tmp = *this;
        return __tmp -= __n;
      }
    
      //返回指定位置的元素，即实现随机存取
      //该函数调用operator+，operator*
      reference operator[](difference_type __n) const { return *(*this + __n); }
    
      bool operator==(const _Self& __x) const { return _M_cur == __x._M_cur; }
      bool operator!=(const _Self& __x) const { return !(*this == __x); }
      bool operator<(const _Self& __x) const {
        return (_M_node == __x._M_node) ? 
          (_M_cur < __x._M_cur) : (_M_node < __x._M_node);
      }
      bool operator>(const _Self& __x) const  { return __x < *this; }
      bool operator<=(const _Self& __x) const { return !(__x < *this); }
      bool operator>=(const _Self& __x) const { return !(*this < __x); }
    
      //调整到正确的缓冲区
      //切换到正确的元素位置
      void _M_set_node(_Map_pointer __new_node) {
        _M_node = __new_node;//指向新的节点
        _M_first = *__new_node;//指向新节点的头部
        _M_last = _M_first + difference_type(_S_buffer_size());//指向新节点的尾部
      }
    };

### deque容器的数据结构 ###

deque容器具有维护 map 和迭代器的功能，deque定义的两个迭代器分别是 start 和 finish ，分别指向第一个缓冲区的第一个元素和最后一个缓冲区的最后一个元素的下一个位置；

template <class _Tp, class _Alloc>
    class _Deque_base {
    	...
    protected:
      _Tp** _M_map;
      size_t _M_map_size;  
      iterator _M_start;
      iterator _M_finish;
      ...
    };
    //deque容器的定义
    //配置器默认为第二级配置器
    template <class _Tp, class _Alloc = __STL_DEFAULT_ALLOCATOR(_Tp) >
    class deque : protected _Deque_base<_Tp, _Alloc> {
    
      // requirements:
    
      ...
    
    public:                         // Iterators
      typedef typename _Base::iterator       iterator;
      typedef typename _Base::const_iterator const_iterator;
    
    protected:
    
      //下面是deque的数据结构
      using _Base::_M_map;//指向中控器map
      using _Base::_M_map_size;//map内指针的个数
      using _Base::_M_start;//指向第一个节点
      using _Base::_M_finish;//指向最后一个节点
      ...
    };

容器的结构图如下所示：

![SouthEast 2][]

### deque容器的构造函数和析构函数 ###

了解deque容器的构造函数和析构函数，方便我们使用；其源码如下：

public:                         
    	//**********************************************************
    	//*	以下是构造函数和析构函数
    	//*	默认构造函数
    	//*	explicit deque( const Allocator& alloc = Allocator() );
    	//*	容器大小为count个初始值为value的元素
    	//*	explicit deque( size_type count,
        //*            const T& value = T(),
        //*            const Allocator& alloc = Allocator());
        //*     deque( size_type count,
        //*            const T& value,
        //*            const Allocator& alloc = Allocator());
    	//*	容器大小为count个默认值的元素
    	//*	explicit deque( size_type count );
    	//*	拷贝构造函数
    	//*	deque( const deque& other );
    	//*	deque( const deque& other, const Allocator& alloc );
    	//*	初始值为[first,last)内容的容器
    	//*	template< class InputIt >
    	//*	deque( InputIt first, InputIt last,
    	//*			const Allocator& alloc = Allocator() );	
    	//*	析构函数
    	//*	~deque()
    	//*
    	//********************************************************
    									// Constructor, destructor.
      explicit deque(const allocator_type& __a = allocator_type()) 
        : _Base(__a, 0) {}
      deque(const deque& __x) : _Base(__x.get_allocator(), __x.size()) 
        { uninitialized_copy(__x.begin(), __x.end(), _M_start); }
      deque(size_type __n, const value_type& __value,
            const allocator_type& __a = allocator_type()) : _Base(__a, __n)
        { _M_fill_initialize(__value); }
      explicit deque(size_type __n) : _Base(allocator_type(), __n)
        { _M_fill_initialize(value_type()); }
    
    #ifdef __STL_MEMBER_TEMPLATES
    
      // Check whether it's an integral type.  If so, it's not an iterator.
      template <class _InputIterator>
      deque(_InputIterator __first, _InputIterator __last,
            const allocator_type& __a = allocator_type()) : _Base(__a) {
        typedef typename _Is_integer<_InputIterator>::_Integral _Integral;
        _M_initialize_dispatch(__first, __last, _Integral());
      }
    
      template <class _Integer>
      void _M_initialize_dispatch(_Integer __n, _Integer __x, __true_type) {
        _M_initialize_map(__n);
        _M_fill_initialize(__x);
      }
    
      template <class _InputIter>
      void _M_initialize_dispatch(_InputIter __first, _InputIter __last,
                                  __false_type) {
        _M_range_initialize(__first, __last, __ITERATOR_CATEGORY(__first));
      }
    
    #else /* __STL_MEMBER_TEMPLATES */
    
      deque(const value_type* __first, const value_type* __last,
            const allocator_type& __a = allocator_type()) 
        : _Base(__a, __last - __first)
        { uninitialized_copy(__first, __last, _M_start); }
      deque(const_iterator __first, const_iterator __last,
            const allocator_type& __a = allocator_type()) 
        : _Base(__a, __last - __first)
        { uninitialized_copy(__first, __last, _M_start); }
    
    #endif /* __STL_MEMBER_TEMPLATES */
    
      ~deque() { destroy(_M_start, _M_finish); }
      //构造函数和析构函数定义结束

### deque容器的成员函数 ###

关于成员函数的讲解，这里只给出源码的剖析：

//交换两个容器的内容
      //这里实际上并没有交换具体的元素，而是交换迭代器
      //和中控器信息
      void swap(deque& __x) {
        __STD::swap(_M_start, __x._M_start);
        __STD::swap(_M_finish, __x._M_finish);
        __STD::swap(_M_map, __x._M_map);
        __STD::swap(_M_map_size, __x._M_map_size);
      }
    
    public: 
      // assign(), a generalized assignment member function.  Two
      // versions: one that takes a count, and one that takes a range.
      // The range version is a member template, so we dispatch on whether
      // or not the type is an integer.
    
      void _M_fill_assign(size_type __n, const _Tp& __val) {
        if (__n > size()) {//若新的大小比容器原来的大
          fill(begin(), end(), __val);//把原来容器填充为val
          insert(end(), __n - size(), __val);//容器追加填充值
        }
        else {//若新的大小比容器原来的小
          erase(begin() + __n, end());//则擦除多余的内容
          fill(begin(), end(), __val);//填充值为val覆盖原来的内容
        }
      }
      //对外接口的assign第一个版本
      void assign(size_type __n, const _Tp& __val) {
        _M_fill_assign(__n, __val);
      }
    
    #ifdef __STL_MEMBER_TEMPLATES
      //对外接口的assign第二个版本
      //采用迭代器的traist技术
      template <class _InputIterator>
      void assign(_InputIterator __first, _InputIterator __last) {
        typedef typename _Is_integer<_InputIterator>::_Integral _Integral;
        _M_assign_dispatch(__first, __last, _Integral());
      }
    
    private:                        // helper functions for assign() 
    
      template <class _Integer>
      void _M_assign_dispatch(_Integer __n, _Integer __val, __true_type)
        { _M_fill_assign((size_type) __n, (_Tp) __val); }
    
      template <class _InputIterator>
      void _M_assign_dispatch(_InputIterator __first, _InputIterator __last,
                              __false_type) {
        _M_assign_aux(__first, __last, __ITERATOR_CATEGORY(__first));
      }
    
      template <class _InputIterator>
      void _M_assign_aux(_InputIterator __first, _InputIterator __last,
                         input_iterator_tag);
    
      template <class _ForwardIterator>
      void _M_assign_aux(_ForwardIterator __first, _ForwardIterator __last,
                         forward_iterator_tag) {
        size_type __len = 0;
        distance(__first, __last, __len);//计算两个输入迭代器的距离
        if (__len > size()) {//若输入迭代器距离比待赋值容器大小还大
          _ForwardIterator __mid = __first;
          advance(__mid, size());//将mid向前移动size()个距离
          copy(__first, __mid, begin());//先复制[first,mid)数据
          insert(end(), __mid, __last);//插入剩下的数据
        }
        else//否则擦除多余的数据
          erase(copy(__first, __last, begin()), end());
      }
    
    #endif /* __STL_MEMBER_TEMPLATES */
    
    
    public:                         // push_* and pop_*
      
      //在容器尾部加数据
    	void push_back(const value_type& __t) {
        //若当前缓冲区存在可用空间
    	if (_M_finish._M_cur != _M_finish._M_last - 1) {
          construct(_M_finish._M_cur, __t);//直接构造对象
          ++_M_finish._M_cur;//调整指针所指位置
        }
        else//若当前缓冲区不存在可用空间
    		//需分配一段新的连续空间
          _M_push_back_aux(__t);
      }
    
      void push_back() {
        if (_M_finish._M_cur != _M_finish._M_last - 1) {
          construct(_M_finish._M_cur);
          ++_M_finish._M_cur;
        }
        else
          _M_push_back_aux();
      }
    
      void push_front(const value_type& __t) {
        if (_M_start._M_cur != _M_start._M_first) {
          construct(_M_start._M_cur - 1, __t);
          --_M_start._M_cur;
        }
        else
          _M_push_front_aux(__t);
      }
    
      void push_front() {
        if (_M_start._M_cur != _M_start._M_first) {
          construct(_M_start._M_cur - 1);
          --_M_start._M_cur;
        }
        else
          _M_push_front_aux();
      }
    
    
      void pop_back() {
        if (_M_finish._M_cur != _M_finish._M_first) {
          --_M_finish._M_cur;
          destroy(_M_finish._M_cur);
        }
        else
          _M_pop_back_aux();
      }
    
      void pop_front() {
        if (_M_start._M_cur != _M_start._M_last - 1) {
          destroy(_M_start._M_cur);
          ++_M_start._M_cur;
        }
        else 
          _M_pop_front_aux();
      }
    
    
    public:             
    	//***********************************************************
    	/*	在指定位置之前插入数据
    	*************************************************************
    	*	iterator insert (iterator position, const value_type& val);
    	*
        *	void insert (iterator position, size_type n, const value_type& val);
    	*
    	*	template <class InputIterator>
        *	void insert (iterator position, InputIterator first, InputIterator last);
    	*/
    	//***********************************************************
    													// Insert
    
      iterator insert(iterator position, const value_type& __x) {
        if (position._M_cur == _M_start._M_cur) {//若当前位置为deque.begin()
          push_front(__x);//则在容器头部插入数据
          return _M_start;
        }
        else if (position._M_cur == _M_finish._M_cur) {//若当前位置为deque.end()
          push_back(__x);
          iterator __tmp = _M_finish;
          --__tmp;
          return __tmp;
        }
        else {//否则在容器直接插入数据
          return _M_insert_aux(position, __x);
        }
      }
    
      iterator insert(iterator __position)
        { return insert(__position, value_type()); }
    
      void insert(iterator __pos, size_type __n, const value_type& __x)
        { _M_fill_insert(__pos, __n, __x); }
    
      void _M_fill_insert(iterator __pos, size_type __n, const value_type& __x); 
    
    #ifdef __STL_MEMBER_TEMPLATES  
    
      // Check whether it's an integral type.  If so, it's not an iterator.
      template <class _InputIterator>
      void insert(iterator __pos, _InputIterator __first, _InputIterator __last) {
        typedef typename _Is_integer<_InputIterator>::_Integral _Integral;
        _M_insert_dispatch(__pos, __first, __last, _Integral());
      }
    
      template <class _Integer>
      void _M_insert_dispatch(iterator __pos, _Integer __n, _Integer __x,
                              __true_type) {
        _M_fill_insert(__pos, (size_type) __n, (value_type) __x);
      }
    
      template <class _InputIterator>
      void _M_insert_dispatch(iterator __pos,
                              _InputIterator __first, _InputIterator __last,
                              __false_type) {
        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 */
    
      //改变容器大小
      void resize(size_type __new_size, const value_type& __x) {
        const size_type __len = size();
        if (__new_size < __len)//新的大小较旧的小 
          erase(_M_start + __new_size, _M_finish);//擦除多余的元素
        else//否则，填充新增的节点
          insert(_M_finish, __new_size - __len, __x);
      }
    
      void resize(size_type new_size) { resize(new_size, value_type()); }
    
    public:          
    		//********************************************************
    		/*	擦除指定位置的元素
    		*	iterator erase (iterator position);
    		*	擦除指定区间的元素
    		*	iterator erase (iterator first, iterator last);
    		*/
    		//********************************************************
    										// Erase
      iterator erase(iterator __pos) {
        iterator __next = __pos;
        ++__next;
        difference_type __index = __pos - _M_start;//擦除点之前元素个数
        if (size_type(__index) < (this->size() >> 1)) {//若擦除点之前的元素个数较少
          copy_backward(_M_start, __pos, __next);//向后移动擦除点之前的元素
          pop_front();
        }
        else {
          copy(__next, _M_finish, __pos);//否则，向前移动擦除点之后的元素
          pop_back();
        }
        return _M_start + __index;
      }
    
      iterator erase(iterator __first, iterator __last);
      void clear(); 
    
    protected:                        // Internal construction/destruction
    
      void _M_fill_initialize(const value_type& __value);
    
    #ifdef __STL_MEMBER_TEMPLATES  
    
      template <class _InputIterator>
      void _M_range_initialize(_InputIterator __first, _InputIterator __last,
                            input_iterator_tag);
    
      template <class _ForwardIterator>
      void _M_range_initialize(_ForwardIterator __first, _ForwardIterator __last,
                            forward_iterator_tag);
    
    #endif /* __STL_MEMBER_TEMPLATES */
    
    protected:                        // Internal push_* and pop_*
    
      void _M_push_back_aux(const value_type&);
      void _M_push_back_aux();
      void _M_push_front_aux(const value_type&);
      void _M_push_front_aux();
      void _M_pop_back_aux();
      void _M_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 _M_insert_aux(iterator __pos, const value_type& __x);
      iterator _M_insert_aux(iterator __pos);
      void _M_insert_aux(iterator __pos, size_type __n, const value_type& __x);
    
    #ifdef __STL_MEMBER_TEMPLATES  
    
      template <class _ForwardIterator>
      void _M_insert_aux(iterator __pos, 
                         _ForwardIterator __first, _ForwardIterator __last,
                         size_type __n);
    
    #else /* __STL_MEMBER_TEMPLATES */
      
      void _M_insert_aux(iterator __pos,
                         const value_type* __first, const value_type* __last,
                         size_type __n);
    
      void _M_insert_aux(iterator __pos, 
                         const_iterator __first, const_iterator __last,
                         size_type __n);
     
    #endif /* __STL_MEMBER_TEMPLATES */
    
      iterator _M_reserve_elements_at_front(size_type __n) {
        size_type __vacancies = _M_start._M_cur - _M_start._M_first;
        if (__n > __vacancies) 
          _M_new_elements_at_front(__n - __vacancies);
        return _M_start - difference_type(__n);
      }
    
      iterator _M_reserve_elements_at_back(size_type __n) {
        size_type __vacancies = (_M_finish._M_last - _M_finish._M_cur) - 1;
        if (__n > __vacancies)
          _M_new_elements_at_back(__n - __vacancies);
        return _M_finish + difference_type(__n);
      }
    
      void _M_new_elements_at_front(size_type __new_elements);
      void _M_new_elements_at_back(size_type __new_elements);
    
    protected:                      // Allocation of _M_map and nodes
    
      // Makes sure the _M_map has space for new nodes.  Does not actually
      //  add the nodes.  Can invalidate _M_map pointers.  (And consequently, 
      //  deque iterators.)
    
      void _M_reserve_map_at_back (size_type __nodes_to_add = 1) {
    	  //_M_map_size - (_M_finish._M_node - _M_map)表示map尾端节点的备用空间
        if (__nodes_to_add + 1 > _M_map_size - (_M_finish._M_node - _M_map))
          _M_reallocate_map(__nodes_to_add, false);
      }
    
      void _M_reserve_map_at_front (size_type __nodes_to_add = 1) {
    	   //_M_start._M_node - _M_map表示map头部节点的备用空间
        if (__nodes_to_add > size_type(_M_start._M_node - _M_map))
          _M_reallocate_map(__nodes_to_add, true);
      }
    
      void _M_reallocate_map(size_type __nodes_to_add, bool __add_at_front);
    };

### deque容器的源码完整剖析 ###

/*	deque是双向队列，可以在头尾两端插入或删除元素；
    *	deque与vector最大的差异就是：
    *	一、deque允许于常数时间内对头端进行插入或删除元素；
    *	二、deque是分段连续线性空间，随时可以增加一段新的空间；
    *	deque不像vector那样，vector当内存不够时，需重新分配/复制数据/释放原始空间；
    *	不过deque的迭代器设置比vector复杂，因为迭代器不能使用普通指针，因此尽量使用vector；
    *	注：当对deque的元素进行排序时，为了提高效率，首先把deque数据复制到vector，
    *	利用vector的排序算法(利用STL的sort算法)，排序之后再次复制回deque； 
    */
    
    #include <concept_checks.h>
    
    #ifndef __SGI_STL_INTERNAL_DEQUE_H
    #define __SGI_STL_INTERNAL_DEQUE_H
    
    /* Class invariants:
     *  For any nonsingular iterator i:
     *    i.node is the address of an element in the map array.  The
     *      contents of i.node is a pointer to the beginning of a node.
     *    i.first == *(i.node) 
     *    i.last  == i.first + node_size
     *    i.cur is a pointer in the range [i.first, i.last).  NOTE:
     *      the implication of this is that i.cur is always a dereferenceable
     *      pointer, even if i is a past-the-end iterator.
     *  Start and Finish are always nonsingular iterators.  NOTE: this means
     *    that an empty deque must have one node, and that a deque
     *    with N elements, where N is the buffer size, must have two nodes.
     *  For every node other than start.node and finish.node, every element
     *    in the node is an initialized object.  If start.node == finish.node,
     *    then [start.cur, finish.cur) are initialized objects, and
     *    the elements outside that range are uninitialized storage.  Otherwise,
     *    [start.cur, start.last) and [finish.first, finish.cur) are initialized
     *    objects, and [start.first, start.cur) and [finish.cur, finish.last)
     *    are uninitialized storage.
     *  [map, map + map_size) is a valid, non-empty range.  
     *  [start.node, finish.node] is a valid range contained within 
     *    [map, map + map_size).  
     *  A pointer in the range [map, map + map_size) points to an allocated node
     *    if and only if the pointer is in the range [start.node, finish.node].
     */
    
    
    /*
     * In previous versions of deque, there was an extra template 
     * parameter so users could control the node size.  This extension
     * turns out to violate the C++ standard (it can be detected using
     * template template parameters), and it has been removed.
     */
    
    __STL_BEGIN_NAMESPACE 
    
    #if defined(__sgi) && !defined(__GNUC__) && (_MIPS_SIM != _MIPS_SIM_ABI32)
    #pragma set woff 1174
    #pragma set woff 1375
    #endif
    
    //*	deque是分段连续线性空间，为了能够像连续线性空间那样访问数据，
    //*	deque采用了一种中控方法map,map是块连续的空间，其每个元素都是一个指针，
    //*	指向一块缓冲区，实质上map是T**；
    //***************************************************************
    
    // Note: this function is simply a kludge to work around several compilers'
    //  bugs in handling constant expressions.
    //这个函数是方便不同编译器处理常量表达式的bug
    inline size_t __deque_buf_size(size_t __size) {
      return __size < 512 ? size_t(512 / __size) : size_t(1);
    }
    
    //deque迭代器的设计
    //*deque是分段连续的线性空间，迭代器设计时必须能够进行operator++或operator--操作
    //*	迭代器的功能：
    //*	1、必须知道缓冲区的位置
    //*	2、能够判断是否处于其所在缓冲区的边界
    //*	3、能够知道其所在缓冲区当前所指位置的元素
    //********************************************
    template <class _Tp, class _Ref, class _Ptr>
    struct _Deque_iterator {
      typedef _Deque_iterator<_Tp, _Tp&, _Tp*>             iterator;
      typedef _Deque_iterator<_Tp, const _Tp&, const _Tp*> const_iterator;
      static size_t _S_buffer_size() { return __deque_buf_size(sizeof(_Tp)); }
    
      typedef random_access_iterator_tag iterator_category;
      typedef _Tp value_type;
      typedef _Ptr pointer;
      typedef _Ref reference;
      typedef size_t size_type;
      typedef ptrdiff_t difference_type;
      typedef _Tp** _Map_pointer;
    
      typedef _Deque_iterator _Self;
    
      //以下是迭代器设计的关键，访问容器的节点
      _Tp* _M_cur;//指向缓冲区当前的元素
      _Tp* _M_first;//指向缓冲区的头(起始地址)
      _Tp* _M_last;//指向缓冲区的尾(结束地址)
      _Map_pointer _M_node;//指向中控器的相应节点
    
      _Deque_iterator(_Tp* __x, _Map_pointer __y) 
        : _M_cur(__x), _M_first(*__y),
          _M_last(*__y + _S_buffer_size()), _M_node(__y) {}
      _Deque_iterator() : _M_cur(0), _M_first(0), _M_last(0), _M_node(0) {}
      _Deque_iterator(const iterator& __x)
        : _M_cur(__x._M_cur), _M_first(__x._M_first), 
          _M_last(__x._M_last), _M_node(__x._M_node) {}
    
      //****************************************************************************
      //*********************以下是迭代器_Deque_iterator的操作**********************
      //*	这些操作符的重载方便我们访问容器的内容
      //*	也是让deque从接口看来是维护连续线性空间的关键
      //****************************************************************************
      reference operator*() const { return *_M_cur; }//解除引用,返回当前元素
    #ifndef __SGI_STL_NO_ARROW_OPERATOR
      pointer operator->() const { return _M_cur; }
    #endif /* __SGI_STL_NO_ARROW_OPERATOR */
    
      //返回两个迭代器之间的距离
      difference_type operator-(const _Self& __x) const {
        return difference_type(_S_buffer_size()) * (_M_node - __x._M_node - 1) +
          (_M_cur - _M_first) + (__x._M_last - __x._M_cur);
      }
    
      //前缀自增++操作符重载
      _Self& operator++() {
        ++_M_cur;					//普通自增操作，移至下一个元素
        if (_M_cur == _M_last) {   //若已达到缓冲区的尾部
          _M_set_node(_M_node + 1);//切换至下一缓冲区(节点)
          _M_cur = _M_first;	  //的第一个元素
        }
        return *this;
      }
      //后缀自增++操作符重载
      //返回当前迭代器的一个副本
      _Self operator++(int)  {
        _Self __tmp = *this;//定义当前迭代器的一个副本
        ++*this;//这里前缀++不是普通的++操作，是上一步骤已经重载过的前缀++
        return __tmp;
      }
    
      //前缀自减--操作符重载
      //基本思想类似于前缀自增操作
      _Self& operator--() {
        if (_M_cur == _M_first) {  //若是当前缓冲区的第一个元素
          _M_set_node(_M_node - 1);//切换到上一个缓冲区
          _M_cur = _M_last;		  //的尾部(即最后一个元素的下一个位置)
        }
        --_M_cur;//普通的自减操作，移至前一个元素
        return *this;
      }
      //后缀自减--操作符重载
      //返回当前迭代器的副本
      _Self operator--(int) {
        _Self __tmp = *this;//定义一个副本
        --*this;			//迭代器自减操作
        return __tmp;
      }
    
      //以下实现随机存取，迭代器可以直接跳跃n个距离
      //将迭代器前移n个距离，当n负值时就为下面的operator-=操作
      _Self& operator+=(difference_type __n)
      {
        difference_type __offset = __n + (_M_cur - _M_first);//定义一个中间变量
        if (__offset >= 0 && __offset < difference_type(_S_buffer_size()))
    		//若前移n个距离后，目标依然在同一个缓冲区
    		//则直接前移n个距离
          _M_cur += __n;
        else {
    		//若前移n个距离后，目标超出该缓冲区范围
    		//__offset / difference_type(_S_buffer_size())计算向后移动多少个缓冲区
    		//-difference_type((-__offset - 1) / _S_buffer_size()) - 1计算向前移动多少个缓冲区
          difference_type __node_offset =
            __offset > 0 ? __offset / difference_type(_S_buffer_size())
                       : -difference_type((-__offset - 1) / _S_buffer_size()) - 1;
    	  //调整到正确的缓冲区
          _M_set_node(_M_node + __node_offset);
    	  //切换至正确的元素
          _M_cur = _M_first + 
            (__offset - __node_offset * difference_type(_S_buffer_size()));
        }
        return *this;
      }
    
      //操作符+重载
      //返回操作之后的副本
      _Self operator+(difference_type __n) const
      {
        _Self __tmp = *this;
    	//调用operator+=操作
        return __tmp += __n;
      }
    
      //利用operator+=操作实现
      _Self& operator-=(difference_type __n) { return *this += -__n; }
     
      _Self operator-(difference_type __n) const {
        _Self __tmp = *this;
        return __tmp -= __n;
      }
    
      //返回指定位置的元素，即实现随机存取
      //该函数调用operator+，operator*
      reference operator[](difference_type __n) const { return *(*this + __n); }
    
      bool operator==(const _Self& __x) const { return _M_cur == __x._M_cur; }
      bool operator!=(const _Self& __x) const { return !(*this == __x); }
      bool operator<(const _Self& __x) const {
        return (_M_node == __x._M_node) ? 
          (_M_cur < __x._M_cur) : (_M_node < __x._M_node);
      }
      bool operator>(const _Self& __x) const  { return __x < *this; }
      bool operator<=(const _Self& __x) const { return !(__x < *this); }
      bool operator>=(const _Self& __x) const { return !(*this < __x); }
    
      //调整到正确的缓冲区
      //切换到正确的元素位置
      void _M_set_node(_Map_pointer __new_node) {
        _M_node = __new_node;//指向新的节点
        _M_first = *__new_node;//指向新节点的头部
        _M_last = _M_first + difference_type(_S_buffer_size());//指向新节点的尾部
      }
    };
    
    //operator+迭代器向前移动n个位置
    template <class _Tp, class _Ref, class _Ptr>
    inline _Deque_iterator<_Tp, _Ref, _Ptr>
    operator+(ptrdiff_t __n, const _Deque_iterator<_Tp, _Ref, _Ptr>& __x)
    {
      return __x + __n;
    }
    
    #ifndef __STL_CLASS_PARTIAL_SPECIALIZATION
    
    template <class _Tp, class _Ref, class _Ptr>
    inline random_access_iterator_tag
    iterator_category(const _Deque_iterator<_Tp,_Ref,_Ptr>&)
    {
      return random_access_iterator_tag();
    }
    
    template <class _Tp, class _Ref, class _Ptr>
    inline _Tp* value_type(const _Deque_iterator<_Tp,_Ref,_Ptr>&) { return 0; }
    
    template <class _Tp, class _Ref, class _Ptr>
    inline ptrdiff_t* distance_type(const _Deque_iterator<_Tp,_Ref,_Ptr>&) {
      return 0;
    }
    
    #endif /* __STL_CLASS_PARTIAL_SPECIALIZATION */
    
    // Deque base class.  It has two purposes.  First, its constructor
    //  and destructor allocate (but don't initialize) storage.  This makes
    //  exception safety easier.  Second, the base class encapsulates all of
    //  the differences between SGI-style allocators and standard-conforming
    //  allocators.
    
    #ifdef __STL_USE_STD_ALLOCATORS
    
    // Base class for ordinary allocators.
    //这里只负责中控器节点内存管理
    template <class _Tp, class _Alloc, bool __is_static>
    class _Deque_alloc_base {
    public:
      typedef typename _Alloc_traits<_Tp,_Alloc>::allocator_type allocator_type;
      allocator_type get_allocator() const { return _M_node_allocator; }
    
      _Deque_alloc_base(const allocator_type& __a)
        : _M_node_allocator(__a), _M_map_allocator(__a),
          _M_map(0), _M_map_size(0)
      {}
      
    protected:
      typedef typename _Alloc_traits<_Tp*, _Alloc>::allocator_type
              _Map_allocator_type;
    
      allocator_type      _M_node_allocator;
      _Map_allocator_type _M_map_allocator;
    
      _Tp* _M_allocate_node() {
        return _M_node_allocator.allocate(__deque_buf_size(sizeof(_Tp)));
      }
      void _M_deallocate_node(_Tp* __p) {
        _M_node_allocator.deallocate(__p, __deque_buf_size(sizeof(_Tp)));
      }
      _Tp** _M_allocate_map(size_t __n) 
        { return _M_map_allocator.allocate(__n); }
      void _M_deallocate_map(_Tp** __p, size_t __n) 
        { _M_map_allocator.deallocate(__p, __n); }
    
      _Tp** _M_map; //指向中控器map
      size_t _M_map_size;//中控器map可容纳指针的个数
    };
    
    // Specialization for instanceless allocators.
    template <class _Tp, class _Alloc>
    class _Deque_alloc_base<_Tp, _Alloc, true>
    {
    public:
      typedef typename _Alloc_traits<_Tp,_Alloc>::allocator_type allocator_type;
      allocator_type get_allocator() const { return allocator_type(); }
    
      _Deque_alloc_base(const allocator_type&) : _M_map(0), _M_map_size(0) {}
      
    protected:
      typedef typename _Alloc_traits<_Tp, _Alloc>::_Alloc_type _Node_alloc_type;
      typedef typename _Alloc_traits<_Tp*, _Alloc>::_Alloc_type _Map_alloc_type;
    
      _Tp* _M_allocate_node() {
        return _Node_alloc_type::allocate(__deque_buf_size(sizeof(_Tp)));
      }
      void _M_deallocate_node(_Tp* __p) {
        _Node_alloc_type::deallocate(__p, __deque_buf_size(sizeof(_Tp)));
      }
      _Tp** _M_allocate_map(size_t __n) 
        { return _Map_alloc_type::allocate(__n); }
      void _M_deallocate_map(_Tp** __p, size_t __n) 
        { _Map_alloc_type::deallocate(__p, __n); }
    
      _Tp** _M_map;
      size_t _M_map_size;
    };
    
    template <class _Tp, class _Alloc>
    class _Deque_base
      : public _Deque_alloc_base<_Tp,_Alloc,
                                  _Alloc_traits<_Tp, _Alloc>::_S_instanceless>
    {
    public:
      typedef _Deque_alloc_base<_Tp,_Alloc,
                                 _Alloc_traits<_Tp, _Alloc>::_S_instanceless>
              _Base;
      typedef typename _Base::allocator_type allocator_type;
      typedef _Deque_iterator<_Tp,_Tp&,_Tp*>             iterator;
      typedef _Deque_iterator<_Tp,const _Tp&,const _Tp*> const_iterator;
    
      //参数__num_elements表示缓冲区(节点)存储元素的个数
      _Deque_base(const allocator_type& __a, size_t __num_elements)
        : _Base(__a), _M_start(), _M_finish()
        { _M_initialize_map(__num_elements); }
      _Deque_base(const allocator_type& __a) 
        : _Base(__a), _M_start(), _M_finish() {}
      ~_Deque_base();    
    
    protected:
      void _M_initialize_map(size_t);
      void _M_create_nodes(_Tp** __nstart, _Tp** __nfinish);
      void _M_destroy_nodes(_Tp** __nstart, _Tp** __nfinish);
      enum { _S_initial_map_size = 8 };//中控器map默认大小
    
    protected:
      iterator _M_start;//指向第一个缓冲区的第一个元素
      iterator _M_finish;//指向最后一个缓冲区的最后一个元素的下一个位置
    };
    
    #else /* __STL_USE_STD_ALLOCATORS */
    
    template <class _Tp, class _Alloc>
    class _Deque_base {
    public:
      typedef _Deque_iterator<_Tp,_Tp&,_Tp*>             iterator;
      typedef _Deque_iterator<_Tp,const _Tp&,const _Tp*> const_iterator;
    
      typedef _Alloc allocator_type;
      allocator_type get_allocator() const { return allocator_type(); }
    
      _Deque_base(const allocator_type&, size_t __num_elements)
        : _M_map(0), _M_map_size(0),  _M_start(), _M_finish() {
        _M_initialize_map(__num_elements);
      }
      _Deque_base(const allocator_type&)
        : _M_map(0), _M_map_size(0),  _M_start(), _M_finish() {}
      ~_Deque_base();    
    
    protected:
      void _M_initialize_map(size_t);
      void _M_create_nodes(_Tp** __nstart, _Tp** __nfinish);
      void _M_destroy_nodes(_Tp** __nstart, _Tp** __nfinish);
      enum { _S_initial_map_size = 8 };
    
    protected:
      _Tp** _M_map;
      size_t _M_map_size;  
      iterator _M_start;
      iterator _M_finish;
    
      typedef simple_alloc<_Tp, _Alloc>  _Node_alloc_type;
      typedef simple_alloc<_Tp*, _Alloc> _Map_alloc_type;
    
      _Tp* _M_allocate_node()
        { return _Node_alloc_type::allocate(__deque_buf_size(sizeof(_Tp))); }
      void _M_deallocate_node(_Tp* __p)
        { _Node_alloc_type::deallocate(__p, __deque_buf_size(sizeof(_Tp))); }
      _Tp** _M_allocate_map(size_t __n) 
        { return _Map_alloc_type::allocate(__n); }
      void _M_deallocate_map(_Tp** __p, size_t __n) 
        { _Map_alloc_type::deallocate(__p, __n); }
    };
    
    #endif /* __STL_USE_STD_ALLOCATORS */
    
    // Non-inline member functions from _Deque_base.
    
    template <class _Tp, class _Alloc>
    _Deque_base<_Tp,_Alloc>::~_Deque_base() {
      if (_M_map) {
        _M_destroy_nodes(_M_start._M_node, _M_finish._M_node + 1);
        _M_deallocate_map(_M_map, _M_map_size);
      }
    }
    
    template <class _Tp, class _Alloc>
    void
    _Deque_base<_Tp,_Alloc>::_M_initialize_map(size_t __num_elements)
    {
       //根据存储元素个数和缓冲区大小决定中控器map容量
    	size_t __num_nodes = 
    		__num_elements / __deque_buf_size(sizeof(_Tp)) + 1;
    
      //在默认值和计算值中，取其最大者
    	//map管理的节点，最少是8个，最多是所需节点数加上2个
    	//前后各预留一个，方便扩充
      _M_map_size = max((size_t) _S_initial_map_size, __num_nodes + 2);
      _M_map = _M_allocate_map(_M_map_size);//分配map内存空间
    
      //让start.node和finish.node指向map的内部，方便map的两端扩充
      _Tp** __nstart = _M_map + (_M_map_size - __num_nodes) / 2;
      _Tp** __nfinish = __nstart + __num_nodes;
        
      __STL_TRY {
        _M_create_nodes(__nstart, __nfinish);//分配map实际存储的节点数空间
      }
      __STL_UNWIND((_M_deallocate_map(_M_map, _M_map_size), 
                    _M_map = 0, _M_map_size = 0));
      _M_start._M_set_node(__nstart);//使迭代器start指向正确的位置
      _M_finish._M_set_node(__nfinish - 1);//使迭代器start指向正确的位置
      _M_start._M_cur = _M_start._M_first;//初始化start.cur,使其指向第一个缓冲区的第一个元素
      //初始化finish.cur,使其指向最后一个缓冲区的最后一个元素
      _M_finish._M_cur = _M_finish._M_first +
                   __num_elements % __deque_buf_size(sizeof(_Tp));
    }
    
    //分配map实际存储的节点数空间
    template <class _Tp, class _Alloc>
    void _Deque_base<_Tp,_Alloc>::_M_create_nodes(_Tp** __nstart, _Tp** __nfinish)
    {
      _Tp** __cur;
      __STL_TRY {
        for (__cur = __nstart; __cur < __nfinish; ++__cur)
          *__cur = _M_allocate_node();
      }
      __STL_UNWIND(_M_destroy_nodes(__nstart, __cur));
    }
    //释放map的节点数空间
    template <class _Tp, class _Alloc>
    void
    _Deque_base<_Tp,_Alloc>::_M_destroy_nodes(_Tp** __nstart, _Tp** __nfinish)
    {
      for (_Tp** __n = __nstart; __n < __nfinish; ++__n)
        _M_deallocate_node(*__n);
    }
    
    //deque容器的定义
    //配置器默认为第二级配置器
    template <class _Tp, class _Alloc = __STL_DEFAULT_ALLOCATOR(_Tp) >
    class deque : protected _Deque_base<_Tp, _Alloc> {
    
      // requirements:
    
      __STL_CLASS_REQUIRES(_Tp, _Assignable);
    
      typedef _Deque_base<_Tp, _Alloc> _Base;
    public:                         // Basic types
      typedef _Tp 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;
    
      typedef typename _Base::allocator_type allocator_type;
      allocator_type get_allocator() const { return _Base::get_allocator(); }
    
    public:                         // Iterators
      typedef typename _Base::iterator       iterator;
      typedef typename _Base::const_iterator const_iterator;
    
    #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
      typedef pointer* _Map_pointer;
      static size_t _S_buffer_size() { return __deque_buf_size(sizeof(_Tp)); }
    
    protected:
    	//继承基类的成员
    #ifdef __STL_USE_NAMESPACES
      using _Base::_M_initialize_map;
      using _Base::_M_create_nodes;
      using _Base::_M_destroy_nodes;
      using _Base::_M_allocate_node;
      using _Base::_M_deallocate_node;
      using _Base::_M_allocate_map;
      using _Base::_M_deallocate_map;
    
      //下面是deque的数据结构
      using _Base::_M_map;
      using _Base::_M_map_size;
      using _Base::_M_start;
      using _Base::_M_finish;
    #endif /* __STL_USE_NAMESPACES */
    
    public:                         // Basic accessors
      iterator begin() { return _M_start; }
      iterator end() { return _M_finish; }
      const_iterator begin() const { return _M_start; }
      const_iterator end() const { return _M_finish; }
    
      reverse_iterator rbegin() { return reverse_iterator(_M_finish); }
      reverse_iterator rend() { return reverse_iterator(_M_start); }
      const_reverse_iterator rbegin() const 
        { return const_reverse_iterator(_M_finish); }
      const_reverse_iterator rend() const 
        { return const_reverse_iterator(_M_start); }
    
      //随机访问，这里调用迭代器的重载操作operator[]
      reference operator[](size_type __n)
        { return _M_start[difference_type(__n)]; }
      const_reference operator[](size_type __n) const 
        { return _M_start[difference_type(__n)]; }
    
    //越界检查
    #ifdef __STL_THROW_RANGE_ERRORS
      void _M_range_check(size_type __n) const {
        if (__n >= this->size())
          __stl_throw_range_error("deque");
      }
    
      //访问指定位置的元素
      reference at(size_type __n)
        { _M_range_check(__n); return (*this)[__n]; }
      const_reference at(size_type __n) const
        { _M_range_check(__n); return (*this)[__n]; }
    #endif /* __STL_THROW_RANGE_ERRORS */
    
      //返回第一个缓冲区的第一个元素
      //调用迭代器的operator*
      reference front() { return *_M_start; }
      //返回最后一个缓冲区的最后一个元素
      reference back() {
        iterator __tmp = _M_finish;
        --__tmp;//调用迭代器的operator--
        return *__tmp;//调用迭代器的operator*
      }
      const_reference front() const { return *_M_start; }
      const_reference back() const {
        const_iterator __tmp = _M_finish;
        --__tmp;
        return *__tmp;
      }
    
      //返回deque容器大小，即容器元素个数
      //调用迭代器的operator-
      size_type size() const { return _M_finish - _M_start; }
      size_type max_size() const { return size_type(-1); }
      //判断容器是否为空
      /*Start and Finish are always nonsingular iterators.  NOTE: this means
       *    that an empty deque must have one node
       */
      bool empty() const { return _M_finish == _M_start; }
    
    public:                         
    	//**********************************************************
    	//*	以下是构造函数和析构函数
    	//*	默认构造函数
    	//*	explicit deque( const Allocator& alloc = Allocator() );
    	//*	容器大小为count个初始值为value的元素
    	//*	explicit deque( size_type count,
        //*            const T& value = T(),
        //*            const Allocator& alloc = Allocator());
        //*     deque( size_type count,
        //*            const T& value,
        //*            const Allocator& alloc = Allocator());
    	//*	容器大小为count个默认值的元素
    	//*	explicit deque( size_type count );
    	//*	拷贝构造函数
    	//*	deque( const deque& other );
    	//*	deque( const deque& other, const Allocator& alloc );
    	//*	初始值为[first,last)内容的容器
    	//*	template< class InputIt >
    	//*	deque( InputIt first, InputIt last,
    	//*			const Allocator& alloc = Allocator() );	
    	//*	析构函数
    	//*	~deque()
    	//*
    	//********************************************************
    									// Constructor, destructor.
      explicit deque(const allocator_type& __a = allocator_type()) 
        : _Base(__a, 0) {}
      deque(const deque& __x) : _Base(__x.get_allocator(), __x.size()) 
        { uninitialized_copy(__x.begin(), __x.end(), _M_start); }
      deque(size_type __n, const value_type& __value,
            const allocator_type& __a = allocator_type()) : _Base(__a, __n)
        { _M_fill_initialize(__value); }
      explicit deque(size_type __n) : _Base(allocator_type(), __n)
        { _M_fill_initialize(value_type()); }
    
    #ifdef __STL_MEMBER_TEMPLATES
    
      // Check whether it's an integral type.  If so, it's not an iterator.
      template <class _InputIterator>
      deque(_InputIterator __first, _InputIterator __last,
            const allocator_type& __a = allocator_type()) : _Base(__a) {
        typedef typename _Is_integer<_InputIterator>::_Integral _Integral;
        _M_initialize_dispatch(__first, __last, _Integral());
      }
    
      template <class _Integer>
      void _M_initialize_dispatch(_Integer __n, _Integer __x, __true_type) {
        _M_initialize_map(__n);
        _M_fill_initialize(__x);
      }
    
      template <class _InputIter>
      void _M_initialize_dispatch(_InputIter __first, _InputIter __last,
                                  __false_type) {
        _M_range_initialize(__first, __last, __ITERATOR_CATEGORY(__first));
      }
    
    #else /* __STL_MEMBER_TEMPLATES */
    
      deque(const value_type* __first, const value_type* __last,
            const allocator_type& __a = allocator_type()) 
        : _Base(__a, __last - __first)
        { uninitialized_copy(__first, __last, _M_start); }
      deque(const_iterator __first, const_iterator __last,
            const allocator_type& __a = allocator_type()) 
        : _Base(__a, __last - __first)
        { uninitialized_copy(__first, __last, _M_start); }
    
    #endif /* __STL_MEMBER_TEMPLATES */
    
      ~deque() { destroy(_M_start, _M_finish); }
      //构造函数和析构函数定义结束
    
     //容器对象赋值操作
      deque& operator= (const deque& __x) {
        const size_type __len = size();
        if (&__x != this) {
          if (__len >= __x.size())
            erase(copy(__x.begin(), __x.end(), _M_start), _M_finish);
          else {
            const_iterator __mid = __x.begin() + difference_type(__len);
            copy(__x.begin(), __mid, _M_start);
            insert(_M_finish, __mid, __x.end());
          }
        }
        return *this;
      }        
    
      //交换两个容器的内容
      //这里实际上并没有交换具体的元素，而是交换迭代器
      //和中控器信息
      void swap(deque& __x) {
        __STD::swap(_M_start, __x._M_start);
        __STD::swap(_M_finish, __x._M_finish);
        __STD::swap(_M_map, __x._M_map);
        __STD::swap(_M_map_size, __x._M_map_size);
      }
    
    public: 
      // assign(), a generalized assignment member function.  Two
      // versions: one that takes a count, and one that takes a range.
      // The range version is a member template, so we dispatch on whether
      // or not the type is an integer.
    
      void _M_fill_assign(size_type __n, const _Tp& __val) {
        if (__n > size()) {//若新的大小比容器原来的大
          fill(begin(), end(), __val);//把原来容器填充为val
          insert(end(), __n - size(), __val);//容器追加填充值
        }
        else {//若新的大小比容器原来的小
          erase(begin() + __n, end());//则擦除多余的内容
          fill(begin(), end(), __val);//填充值为val覆盖原来的内容
        }
      }
      //对外接口的assign第一个版本
      void assign(size_type __n, const _Tp& __val) {
        _M_fill_assign(__n, __val);
      }
    
    #ifdef __STL_MEMBER_TEMPLATES
      //对外接口的assign第二个版本
      //采用迭代器的traist技术
      template <class _InputIterator>
      void assign(_InputIterator __first, _InputIterator __last) {
        typedef typename _Is_integer<_InputIterator>::_Integral _Integral;
        _M_assign_dispatch(__first, __last, _Integral());
      }
    
    private:                        // helper functions for assign() 
    
      template <class _Integer>
      void _M_assign_dispatch(_Integer __n, _Integer __val, __true_type)
        { _M_fill_assign((size_type) __n, (_Tp) __val); }
    
      template <class _InputIterator>
      void _M_assign_dispatch(_InputIterator __first, _InputIterator __last,
                              __false_type) {
        _M_assign_aux(__first, __last, __ITERATOR_CATEGORY(__first));
      }
    
      template <class _InputIterator>
      void _M_assign_aux(_InputIterator __first, _InputIterator __last,
                         input_iterator_tag);
    
      template <class _ForwardIterator>
      void _M_assign_aux(_ForwardIterator __first, _ForwardIterator __last,
                         forward_iterator_tag) {
        size_type __len = 0;
        distance(__first, __last, __len);//计算两个输入迭代器的距离
        if (__len > size()) {//若输入迭代器距离比待赋值容器大小还大
          _ForwardIterator __mid = __first;
          advance(__mid, size());//将mid向前移动size()个距离
          copy(__first, __mid, begin());//先复制[first,mid)数据
          insert(end(), __mid, __last);//插入剩下的数据
        }
        else//否则擦除多余的数据
          erase(copy(__first, __last, begin()), end());
      }
    
    #endif /* __STL_MEMBER_TEMPLATES */
    
    
    public:                         // push_* and pop_*
      
      //在容器尾部加数据
    	void push_back(const value_type& __t) {
        //若当前缓冲区存在可用空间
    	if (_M_finish._M_cur != _M_finish._M_last - 1) {
          construct(_M_finish._M_cur, __t);//直接构造对象
          ++_M_finish._M_cur;//调整指针所指位置
        }
        else//若当前缓冲区不存在可用空间
    		//需分配一段新的连续空间
          _M_push_back_aux(__t);
      }
    
      void push_back() {
        if (_M_finish._M_cur != _M_finish._M_last - 1) {
          construct(_M_finish._M_cur);
          ++_M_finish._M_cur;
        }
        else
          _M_push_back_aux();
      }
    
      void push_front(const value_type& __t) {
        if (_M_start._M_cur != _M_start._M_first) {
          construct(_M_start._M_cur - 1, __t);
          --_M_start._M_cur;
        }
        else
          _M_push_front_aux(__t);
      }
    
      void push_front() {
        if (_M_start._M_cur != _M_start._M_first) {
          construct(_M_start._M_cur - 1);
          --_M_start._M_cur;
        }
        else
          _M_push_front_aux();
      }
    
    
      void pop_back() {
        if (_M_finish._M_cur != _M_finish._M_first) {
          --_M_finish._M_cur;
          destroy(_M_finish._M_cur);
        }
        else
          _M_pop_back_aux();
      }
    
      void pop_front() {
        if (_M_start._M_cur != _M_start._M_last - 1) {
          destroy(_M_start._M_cur);
          ++_M_start._M_cur;
        }
        else 
          _M_pop_front_aux();
      }
    
    
    public:             
    	//***********************************************************
    	/*	在指定位置之前插入数据
    	*************************************************************
    	*	iterator insert (iterator position, const value_type& val);
    	*
        *	void insert (iterator position, size_type n, const value_type& val);
    	*
    	*	template <class InputIterator>
        *	void insert (iterator position, InputIterator first, InputIterator last);
    	*/
    	//***********************************************************
    													// Insert
    
      iterator insert(iterator position, const value_type& __x) {
        if (position._M_cur == _M_start._M_cur) {//若当前位置为deque.begin()
          push_front(__x);//则在容器头部插入数据
          return _M_start;
        }
        else if (position._M_cur == _M_finish._M_cur) {//若当前位置为deque.end()
          push_back(__x);
          iterator __tmp = _M_finish;
          --__tmp;
          return __tmp;
        }
        else {//否则在容器直接插入数据
          return _M_insert_aux(position, __x);
        }
      }
    
      iterator insert(iterator __position)
        { return insert(__position, value_type()); }
    
      void insert(iterator __pos, size_type __n, const value_type& __x)
        { _M_fill_insert(__pos, __n, __x); }
    
      void _M_fill_insert(iterator __pos, size_type __n, const value_type& __x); 
    
    #ifdef __STL_MEMBER_TEMPLATES  
    
      // Check whether it's an integral type.  If so, it's not an iterator.
      template <class _InputIterator>
      void insert(iterator __pos, _InputIterator __first, _InputIterator __last) {
        typedef typename _Is_integer<_InputIterator>::_Integral _Integral;
        _M_insert_dispatch(__pos, __first, __last, _Integral());
      }
    
      template <class _Integer>
      void _M_insert_dispatch(iterator __pos, _Integer __n, _Integer __x,
                              __true_type) {
        _M_fill_insert(__pos, (size_type) __n, (value_type) __x);
      }
    
      template <class _InputIterator>
      void _M_insert_dispatch(iterator __pos,
                              _InputIterator __first, _InputIterator __last,
                              __false_type) {
        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 */
    
      //改变容器大小
      void resize(size_type __new_size, const value_type& __x) {
        const size_type __len = size();
        if (__new_size < __len)//新的大小较旧的小 
          erase(_M_start + __new_size, _M_finish);//擦除多余的元素
        else//否则，填充新增的节点
          insert(_M_finish, __new_size - __len, __x);
      }
    
      void resize(size_type new_size) { resize(new_size, value_type()); }
    
    public:          
    		//********************************************************
    		/*	擦除指定位置的元素
    		*	iterator erase (iterator position);
    		*	擦除指定区间的元素
    		*	iterator erase (iterator first, iterator last);
    		*/
    		//********************************************************
    										// Erase
      iterator erase(iterator __pos) {
        iterator __next = __pos;
        ++__next;
        difference_type __index = __pos - _M_start;//擦除点之前元素个数
        if (size_type(__index) < (this->size() >> 1)) {//若擦除点之前的元素个数较少
          copy_backward(_M_start, __pos, __next);//向后移动擦除点之前的元素
          pop_front();
        }
        else {
          copy(__next, _M_finish, __pos);//否则，向前移动擦除点之后的元素
          pop_back();
        }
        return _M_start + __index;
      }
    
      iterator erase(iterator __first, iterator __last);
      void clear(); 
    
    protected:                        // Internal construction/destruction
    
      void _M_fill_initialize(const value_type& __value);
    
    #ifdef __STL_MEMBER_TEMPLATES  
    
      template <class _InputIterator>
      void _M_range_initialize(_InputIterator __first, _InputIterator __last,
                            input_iterator_tag);
    
      template <class _ForwardIterator>
      void _M_range_initialize(_ForwardIterator __first, _ForwardIterator __last,
                            forward_iterator_tag);
    
    #endif /* __STL_MEMBER_TEMPLATES */
    
    protected:                        // Internal push_* and pop_*
    
      void _M_push_back_aux(const value_type&);
      void _M_push_back_aux();
      void _M_push_front_aux(const value_type&);
      void _M_push_front_aux();
      void _M_pop_back_aux();
      void _M_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 _M_insert_aux(iterator __pos, const value_type& __x);
      iterator _M_insert_aux(iterator __pos);
      void _M_insert_aux(iterator __pos, size_type __n, const value_type& __x);
    
    #ifdef __STL_MEMBER_TEMPLATES  
    
      template <class _ForwardIterator>
      void _M_insert_aux(iterator __pos, 
                         _ForwardIterator __first, _ForwardIterator __last,
                         size_type __n);
    
    #else /* __STL_MEMBER_TEMPLATES */
      
      void _M_insert_aux(iterator __pos,
                         const value_type* __first, const value_type* __last,
                         size_type __n);
    
      void _M_insert_aux(iterator __pos, 
                         const_iterator __first, const_iterator __last,
                         size_type __n);
     
    #endif /* __STL_MEMBER_TEMPLATES */
    
      iterator _M_reserve_elements_at_front(size_type __n) {
        size_type __vacancies = _M_start._M_cur - _M_start._M_first;
        if (__n > __vacancies) 
          _M_new_elements_at_front(__n - __vacancies);
        return _M_start - difference_type(__n);
      }
    
      iterator _M_reserve_elements_at_back(size_type __n) {
        size_type __vacancies = (_M_finish._M_last - _M_finish._M_cur) - 1;
        if (__n > __vacancies)
          _M_new_elements_at_back(__n - __vacancies);
        return _M_finish + difference_type(__n);
      }
    
      void _M_new_elements_at_front(size_type __new_elements);
      void _M_new_elements_at_back(size_type __new_elements);
    
    protected:                      // Allocation of _M_map and nodes
    
      // Makes sure the _M_map has space for new nodes.  Does not actually
      //  add the nodes.  Can invalidate _M_map pointers.  (And consequently, 
      //  deque iterators.)
    
      void _M_reserve_map_at_back (size_type __nodes_to_add = 1) {
    	  //_M_map_size - (_M_finish._M_node - _M_map)表示map尾端节点的备用空间
        if (__nodes_to_add + 1 > _M_map_size - (_M_finish._M_node - _M_map))
          _M_reallocate_map(__nodes_to_add, false);
      }
    
      void _M_reserve_map_at_front (size_type __nodes_to_add = 1) {
    	   //_M_start._M_node - _M_map表示map头部节点的备用空间
        if (__nodes_to_add > size_type(_M_start._M_node - _M_map))
          _M_reallocate_map(__nodes_to_add, true);
      }
    
      void _M_reallocate_map(size_type __nodes_to_add, bool __add_at_front);
    };
    
    // Non-inline member functions
    
    #ifdef __STL_MEMBER_TEMPLATES
    
    template <class _Tp, class _Alloc>
    template <class _InputIter>
    void deque<_Tp, _Alloc>
      ::_M_assign_aux(_InputIter __first, _InputIter __last, input_iterator_tag)
    {
      iterator __cur = begin();
      for ( ; __first != __last && __cur != end(); ++__cur, ++__first)
        *__cur = *__first;
      if (__first == __last)//若当前容器比输入迭代器距离大
        erase(__cur, end());//擦除多余的数据
      else//否则插入剩下的数据
        insert(end(), __first, __last);
    }
    
    #endif /* __STL_MEMBER_TEMPLATES */
    
    template <class _Tp, class _Alloc>
    void deque<_Tp, _Alloc>::_M_fill_insert(iterator __pos,
                                            size_type __n, const value_type& __x)
    {
      if (__pos._M_cur == _M_start._M_cur) {//若插入点在容器头部
        iterator __new_start = _M_reserve_elements_at_front(__n);
        __STL_TRY {
          uninitialized_fill(__new_start, _M_start, __x);
          _M_start = __new_start;
        }
        __STL_UNWIND(_M_destroy_nodes(__new_start._M_node, _M_start._M_node));
      }
      else if (__pos._M_cur == _M_finish._M_cur) {//若插入点在容器尾部
        iterator __new_finish = _M_reserve_elements_at_back(__n);
        __STL_TRY {
          uninitialized_fill(_M_finish, __new_finish, __x);
          _M_finish = __new_finish;
        }
        __STL_UNWIND(_M_destroy_nodes(_M_finish._M_node + 1, 
                                      __new_finish._M_node + 1));    
      }
      else 
        _M_insert_aux(__pos, __n, __x);
    }
    
    #ifndef __STL_MEMBER_TEMPLATES  
    
    template <class _Tp, class _Alloc>
    void deque<_Tp, _Alloc>::insert(iterator __pos,
                                    const value_type* __first,
                                    const value_type* __last) {
      size_type __n = __last - __first;
      if (__pos._M_cur == _M_start._M_cur) {
        iterator __new_start = _M_reserve_elements_at_front(__n);
        __STL_TRY {
          uninitialized_copy(__first, __last, __new_start);
          _M_start = __new_start;
        }
        __STL_UNWIND(_M_destroy_nodes(__new_start._M_node, _M_start._M_node));
      }
      else if (__pos._M_cur == _M_finish._M_cur) {
        iterator __new_finish = _M_reserve_elements_at_back(__n);
        __STL_TRY {
          uninitialized_copy(__first, __last, _M_finish);
          _M_finish = __new_finish;
        }
        __STL_UNWIND(_M_destroy_nodes(_M_finish._M_node + 1, 
                                      __new_finish._M_node + 1));
      }
      else
        _M_insert_aux(__pos, __first, __last, __n);
    }
    
    template <class _Tp, class _Alloc>
    void deque<_Tp,_Alloc>::insert(iterator __pos,
                                   const_iterator __first, const_iterator __last)
    {
      size_type __n = __last - __first;
      if (__pos._M_cur == _M_start._M_cur) {
        iterator __new_start = _M_reserve_elements_at_front(__n);
        __STL_TRY {
          uninitialized_copy(__first, __last, __new_start);
          _M_start = __new_start;
        }
        __STL_UNWIND(_M_destroy_nodes(__new_start._M_node, _M_start._M_node));
      }
      else if (__pos._M_cur == _M_finish._M_cur) {
        iterator __new_finish = _M_reserve_elements_at_back(__n);
        __STL_TRY {
          uninitialized_copy(__first, __last, _M_finish);
          _M_finish = __new_finish;
        }
        __STL_UNWIND(_M_destroy_nodes(_M_finish._M_node + 1, 
                     __new_finish._M_node + 1));
      }
      else
        _M_insert_aux(__pos, __first, __last, __n);
    }
    
    #endif /* __STL_MEMBER_TEMPLATES */
    
    template <class _Tp, class _Alloc>
    typename deque<_Tp,_Alloc>::iterator 
    deque<_Tp,_Alloc>::erase(iterator __first, iterator __last)
    {
      if (__first == _M_start && __last == _M_finish) {//若擦除整个容器内容
        clear();
        return _M_finish;
      }
      else {
        difference_type __n = __last - __first;
        difference_type __elems_before = __first - _M_start;
        if (__elems_before < difference_type((this->size() - __n) / 2)) {
          copy_backward(_M_start, __first, __last);
          iterator __new_start = _M_start + __n;
          destroy(_M_start, __new_start);
          _M_destroy_nodes(__new_start._M_node, _M_start._M_node);
          _M_start = __new_start;
        }
        else {
          copy(__last, _M_finish, __first);
          iterator __new_finish = _M_finish - __n;
          destroy(__new_finish, _M_finish);
          _M_destroy_nodes(__new_finish._M_node + 1, _M_finish._M_node + 1);
          _M_finish = __new_finish;
        }
        return _M_start + __elems_before;
      }
    }
    
    //清空容器内容
    template <class _Tp, class _Alloc> 
    void deque<_Tp,_Alloc>::clear()
    {
      //首先清空缓冲区是满数据的节点
    	for (_Map_pointer __node = _M_start._M_node + 1;
           __node < _M_finish._M_node;
           ++__node) {
        destroy(*__node, *__node + _S_buffer_size());
        _M_deallocate_node(*__node);
      }
    
     //清除缓冲区还存在可用空间的节点，即只存储部分数据
    	if (_M_start._M_node != _M_finish._M_node) {
        destroy(_M_start._M_cur, _M_start._M_last);
        destroy(_M_finish._M_first, _M_finish._M_cur);
        _M_deallocate_node(_M_finish._M_first);
      }
      else
        destroy(_M_start._M_cur, _M_finish._M_cur);
    
      _M_finish = _M_start;//表示容器为空
    }
    
    // Precondition: _M_start and _M_finish have already been initialized,
    // but none of the deque's elements have yet been constructed.
    template <class _Tp, class _Alloc>
    void deque<_Tp,_Alloc>::_M_fill_initialize(const value_type& __value) {
      _Map_pointer __cur;
      __STL_TRY {//为每个节点的缓冲区设置初值
        for (__cur = _M_start._M_node; __cur < _M_finish._M_node; ++__cur)
          uninitialized_fill(*__cur, *__cur + _S_buffer_size(), __value);
    	//最后一个缓冲区必须单独设置初值，因为可能存在可用空间
        uninitialized_fill(_M_finish._M_first, _M_finish._M_cur, __value);
      }
      __STL_UNWIND(destroy(_M_start, iterator(*__cur, __cur)));
    }
    
    #ifdef __STL_MEMBER_TEMPLATES  
    
    template <class _Tp, class _Alloc> template <class _InputIterator>
    void deque<_Tp,_Alloc>::_M_range_initialize(_InputIterator __first,
                                                _InputIterator __last,
                                                input_iterator_tag)
    {
      _M_initialize_map(0);
      __STL_TRY {
        for ( ; __first != __last; ++__first)
          push_back(*__first);
      }
      __STL_UNWIND(clear());
    }
    
    template <class _Tp, class _Alloc> template <class _ForwardIterator>
    void deque<_Tp,_Alloc>::_M_range_initialize(_ForwardIterator __first,
                                                _ForwardIterator __last,
                                                forward_iterator_tag)
    {
      size_type __n = 0;
      distance(__first, __last, __n);
      _M_initialize_map(__n);
    
      _Map_pointer __cur_node;
      __STL_TRY {
        for (__cur_node = _M_start._M_node; 
             __cur_node < _M_finish._M_node; 
             ++__cur_node) {
          _ForwardIterator __mid = __first;
          advance(__mid, _S_buffer_size());
          uninitialized_copy(__first, __mid, *__cur_node);
          __first = __mid;
        }
        uninitialized_copy(__first, __last, _M_finish._M_first);
      }
      __STL_UNWIND(destroy(_M_start, iterator(*__cur_node, __cur_node)));
    }
    
    #endif /* __STL_MEMBER_TEMPLATES */
    
    // Called only if _M_finish._M_cur == _M_finish._M_last - 1.
    template <class _Tp, class _Alloc>
    void deque<_Tp,_Alloc>::_M_push_back_aux(const value_type& __t)
    {
      value_type __t_copy = __t;
      _M_reserve_map_at_back();//调整map
      *(_M_finish._M_node + 1) = _M_allocate_node();//分配一个新的节点
      __STL_TRY {
        construct(_M_finish._M_cur, __t_copy);
        _M_finish._M_set_node(_M_finish._M_node + 1);
        _M_finish._M_cur = _M_finish._M_first;
      }
      __STL_UNWIND(_M_deallocate_node(*(_M_finish._M_node + 1)));
    }
    
    // Called only if _M_finish._M_cur == _M_finish._M_last - 1.
    template <class _Tp, class _Alloc>
    void deque<_Tp,_Alloc>::_M_push_back_aux()
    {
      _M_reserve_map_at_back();
      *(_M_finish._M_node + 1) = _M_allocate_node();
      __STL_TRY {
        construct(_M_finish._M_cur);
        _M_finish._M_set_node(_M_finish._M_node + 1);
        _M_finish._M_cur = _M_finish._M_first;
      }
      __STL_UNWIND(_M_deallocate_node(*(_M_finish._M_node + 1)));
    }
    
    // Called only if _M_start._M_cur == _M_start._M_first.
    template <class _Tp, class _Alloc>
    void  deque<_Tp,_Alloc>::_M_push_front_aux(const value_type& __t)
    {
      value_type __t_copy = __t;
      _M_reserve_map_at_front();
      *(_M_start._M_node - 1) = _M_allocate_node();
      __STL_TRY {
        _M_start._M_set_node(_M_start._M_node - 1);
        _M_start._M_cur = _M_start._M_last - 1;
        construct(_M_start._M_cur, __t_copy);
      }
      __STL_UNWIND((++_M_start, _M_deallocate_node(*(_M_start._M_node - 1))));
    } 
    
    // Called only if _M_start._M_cur == _M_start._M_first.
    template <class _Tp, class _Alloc>
    void deque<_Tp,_Alloc>::_M_push_front_aux()
    {
      _M_reserve_map_at_front();
      *(_M_start._M_node - 1) = _M_allocate_node();
      __STL_TRY {
        _M_start._M_set_node(_M_start._M_node - 1);
        _M_start._M_cur = _M_start._M_last - 1;
        construct(_M_start._M_cur);
      }
      __STL_UNWIND((++_M_start, _M_deallocate_node(*(_M_start._M_node - 1))));
    } 
    
    // Called only if _M_finish._M_cur == _M_finish._M_first.
    template <class _Tp, class _Alloc>
    void deque<_Tp,_Alloc>::_M_pop_back_aux()
    {
      _M_deallocate_node(_M_finish._M_first);
      _M_finish._M_set_node(_M_finish._M_node - 1);
      _M_finish._M_cur = _M_finish._M_last - 1;
      destroy(_M_finish._M_cur);
    }
    
    // Called only if _M_start._M_cur == _M_start._M_last - 1.  Note that 
    // if the deque has at least one element (a precondition for this member 
    // function), and if _M_start._M_cur == _M_start._M_last, then the deque 
    // must have at least two nodes.
    template <class _Tp, class _Alloc>
    void deque<_Tp,_Alloc>::_M_pop_front_aux()
    {
      destroy(_M_start._M_cur);
      _M_deallocate_node(_M_start._M_first);
      _M_start._M_set_node(_M_start._M_node + 1);
      _M_start._M_cur = _M_start._M_first;
    }      
    
    #ifdef __STL_MEMBER_TEMPLATES  
    
    template <class _Tp, class _Alloc> template <class _InputIterator>
    void deque<_Tp,_Alloc>::insert(iterator __pos,
                                   _InputIterator __first, _InputIterator __last,
                                   input_iterator_tag)
    {
      copy(__first, __last, inserter(*this, __pos));
    }
    
    template <class _Tp, class _Alloc> template <class _ForwardIterator>
    void
    deque<_Tp,_Alloc>::insert(iterator __pos,
                              _ForwardIterator __first, _ForwardIterator __last,
                              forward_iterator_tag) {
      size_type __n = 0;
      distance(__first, __last, __n);
      if (__pos._M_cur == _M_start._M_cur) {
        iterator __new_start = _M_reserve_elements_at_front(__n);
        __STL_TRY {
          uninitialized_copy(__first, __last, __new_start);
          _M_start = __new_start;
        }
        __STL_UNWIND(_M_destroy_nodes(__new_start._M_node, _M_start._M_node));
      }
      else if (__pos._M_cur == _M_finish._M_cur) {
        iterator __new_finish = _M_reserve_elements_at_back(__n);
        __STL_TRY {
          uninitialized_copy(__first, __last, _M_finish);
          _M_finish = __new_finish;
        }
        __STL_UNWIND(_M_destroy_nodes(_M_finish._M_node + 1, 
                                      __new_finish._M_node + 1));
      }
      else
        _M_insert_aux(__pos, __first, __last, __n);
    }
    
    #endif /* __STL_MEMBER_TEMPLATES */
    
    template <class _Tp, class _Alloc>
    typename deque<_Tp, _Alloc>::iterator
    deque<_Tp,_Alloc>::_M_insert_aux(iterator __pos, const value_type& __x)
    {
      difference_type __index = __pos - _M_start;//计算插入点之前元素个数
      value_type __x_copy = __x;
      if (size_type(__index) < this->size() / 2) {//若插入点之前的元素较少
        push_front(front());//先在容器头部插入与第一个元素相同的元素
        iterator __front1 = _M_start;
        ++__front1;
        iterator __front2 = __front1;
        ++__front2;
        __pos = _M_start + __index;//这里的pos相较与接受参数的pos已经前移一位了
        iterator __pos1 = __pos;
        ++__pos1;
    	//原型
    	/*
    	*	template<class InputIterator, class OutputIterator>
    	*	OutputIterator copy (InputIterator first, InputIterator last, OutputIterator result)
    	*	{
    	*	  while (first!=last) {
    	*		*result = *first;
    	*		++result; ++first;
    	*	  }
    	*	  return result;
    	*	}
    	*/
        copy(__front2, __pos1, __front1);//移动元素
      }
      else {//若插入点之后的元素较少
        push_back(back());//先在容器尾部插入与最后一个元素相同的元素
        iterator __back1 = _M_finish;
        --__back1;
        iterator __back2 = __back1;
        --__back2;
        __pos = _M_start + __index;//这里的pos与接受参数的pos相同
    	//**原型
    	//*	template<class BidirectionalIterator1, class BidirectionalIterator2>
    	//*	BidirectionalIterator2 copy_backward ( BidirectionalIterator1 first,
        //*                                     BidirectionalIterator1 last,
        //*                                     BidirectionalIterator2 result )
    	//*	{
    	//*	  while (last!=first) *(--result) = *(--last);
    	//*	  return result;
    	//*	}
        copy_backward(__pos, __back2, __back1);//移动元素
      }
      *__pos = __x_copy;
      return __pos;
    }
    
    template <class _Tp, class _Alloc>
    typename deque<_Tp,_Alloc>::iterator 
    deque<_Tp,_Alloc>::_M_insert_aux(iterator __pos)
    {
      difference_type __index = __pos - _M_start;
      if (__index < size() / 2) {
        push_front(front());
        iterator __front1 = _M_start;
        ++__front1;
        iterator __front2 = __front1;
        ++__front2;
        __pos = _M_start + __index;
        iterator __pos1 = __pos;
        ++__pos1;
        copy(__front2, __pos1, __front1);
      }
      else {
        push_back(back());
        iterator __back1 = _M_finish;
        --__back1;
        iterator __back2 = __back1;
        --__back2;
        __pos = _M_start + __index;
        copy_backward(__pos, __back2, __back1);
      }
      *__pos = value_type();
      return __pos;
    }
    
    template <class _Tp, class _Alloc>
    void deque<_Tp,_Alloc>::_M_insert_aux(iterator __pos,
                                          size_type __n,
                                          const value_type& __x)
    {
      const difference_type __elems_before = __pos - _M_start;
      size_type __length = this->size();
      value_type __x_copy = __x;
      if (__elems_before < difference_type(__length / 2)) {
        iterator __new_start = _M_reserve_elements_at_front(__n);
        iterator __old_start = _M_start;
        __pos = _M_start + __elems_before;
        __STL_TRY {
          if (__elems_before >= difference_type(__n)) {
            iterator __start_n = _M_start + difference_type(__n);
            uninitialized_copy(_M_start, __start_n, __new_start);
            _M_start = __new_start;
            copy(__start_n, __pos, __old_start);
            fill(__pos - difference_type(__n), __pos, __x_copy);
          }
          else {
            __uninitialized_copy_fill(_M_start, __pos, __new_start, 
                                      _M_start, __x_copy);
            _M_start = __new_start;
            fill(__old_start, __pos, __x_copy);
          }
        }
        __STL_UNWIND(_M_destroy_nodes(__new_start._M_node, _M_start._M_node));
      }
      else {
        iterator __new_finish = _M_reserve_elements_at_back(__n);
        iterator __old_finish = _M_finish;
        const difference_type __elems_after = 
          difference_type(__length) - __elems_before;
        __pos = _M_finish - __elems_after;
        __STL_TRY {
          if (__elems_after > difference_type(__n)) {
            iterator __finish_n = _M_finish - difference_type(__n);
            uninitialized_copy(__finish_n, _M_finish, _M_finish);
            _M_finish = __new_finish;
            copy_backward(__pos, __finish_n, __old_finish);
            fill(__pos, __pos + difference_type(__n), __x_copy);
          }
          else {
            __uninitialized_fill_copy(_M_finish, __pos + difference_type(__n),
                                      __x_copy, __pos, _M_finish);
            _M_finish = __new_finish;
            fill(__pos, __old_finish, __x_copy);
          }
        }
        __STL_UNWIND(_M_destroy_nodes(_M_finish._M_node + 1, 
                                      __new_finish._M_node + 1));
      }
    }
    
    #ifdef __STL_MEMBER_TEMPLATES  
    
    template <class _Tp, class _Alloc> template <class _ForwardIterator>
    void deque<_Tp,_Alloc>::_M_insert_aux(iterator __pos,
                                          _ForwardIterator __first,
                                          _ForwardIterator __last,
                                          size_type __n)
    {
      const difference_type __elemsbefore = __pos - _M_start;
      size_type __length = size();
      if (__elemsbefore < __length / 2) {
        iterator __new_start = _M_reserve_elements_at_front(__n);
        iterator __old_start = _M_start;
        __pos = _M_start + __elemsbefore;
        __STL_TRY {
          if (__elemsbefore >= difference_type(__n)) {
            iterator __start_n = _M_start + difference_type(__n); 
            uninitialized_copy(_M_start, __start_n, __new_start);
            _M_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) - __elemsbefore);
            __uninitialized_copy_copy(_M_start, __pos, __first, __mid,
                                      __new_start);
            _M_start = __new_start;
            copy(__mid, __last, __old_start);
          }
        }
        __STL_UNWIND(_M_destroy_nodes(__new_start._M_node, _M_start._M_node));
      }
      else {
        iterator __new_finish = _M_reserve_elements_at_back(__n);
        iterator __old_finish = _M_finish;
        const difference_type __elemsafter = 
          difference_type(__length) - __elemsbefore;
        __pos = _M_finish - __elemsafter;
        __STL_TRY {
          if (__elemsafter > difference_type(__n)) {
            iterator __finish_n = _M_finish - difference_type(__n);
            uninitialized_copy(__finish_n, _M_finish, _M_finish);
            _M_finish = __new_finish;
            copy_backward(__pos, __finish_n, __old_finish);
            copy(__first, __last, __pos);
          }
          else {
            _ForwardIterator __mid = __first;
            advance(__mid, __elemsafter);
            __uninitialized_copy_copy(__mid, __last, __pos, _M_finish, _M_finish);
            _M_finish = __new_finish;
            copy(__first, __mid, __pos);
          }
        }
        __STL_UNWIND(_M_destroy_nodes(_M_finish._M_node + 1, 
                                      __new_finish._M_node + 1));
      }
    }
    
    #else /* __STL_MEMBER_TEMPLATES */
    
    template <class _Tp, class _Alloc>
    void deque<_Tp,_Alloc>::_M_insert_aux(iterator __pos,
                                          const value_type* __first,
                                          const value_type* __last,
                                          size_type __n)
    {
      const difference_type __elemsbefore = __pos - _M_start;
      size_type __length = size();
      if (__elemsbefore < __length / 2) {
        iterator __new_start = _M_reserve_elements_at_front(__n);
        iterator __old_start = _M_start;
        __pos = _M_start + __elemsbefore;
        __STL_TRY {
          if (__elemsbefore >= difference_type(__n)) {
            iterator __start_n = _M_start + difference_type(__n);
            uninitialized_copy(_M_start, __start_n, __new_start);
            _M_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) - __elemsbefore);
            __uninitialized_copy_copy(_M_start, __pos, __first, __mid,
                                      __new_start);
            _M_start = __new_start;
            copy(__mid, __last, __old_start);
          }
        }
        __STL_UNWIND(_M_destroy_nodes(__new_start._M_node, _M_start._M_node));
      }
      else {
        iterator __new_finish = _M_reserve_elements_at_back(__n);
        iterator __old_finish = _M_finish;
        const difference_type __elemsafter = 
          difference_type(__length) - __elemsbefore;
        __pos = _M_finish - __elemsafter;
        __STL_TRY {
          if (__elemsafter > difference_type(__n)) {
            iterator __finish_n = _M_finish - difference_type(__n);
            uninitialized_copy(__finish_n, _M_finish, _M_finish);
            _M_finish = __new_finish;
            copy_backward(__pos, __finish_n, __old_finish);
            copy(__first, __last, __pos);
          }
          else {
            const value_type* __mid = __first + __elemsafter;
            __uninitialized_copy_copy(__mid, __last, __pos, _M_finish, _M_finish);
            _M_finish = __new_finish;
            copy(__first, __mid, __pos);
          }
        }
        __STL_UNWIND(_M_destroy_nodes(_M_finish._M_node + 1, 
                                      __new_finish._M_node + 1));
      }
    }
    
    template <class _Tp, class _Alloc>
    void deque<_Tp,_Alloc>::_M_insert_aux(iterator __pos,
                                          const_iterator __first,
                                          const_iterator __last,
                                          size_type __n)
    {
      const difference_type __elemsbefore = __pos - _M_start;
      size_type __length = size();
      if (__elemsbefore < __length / 2) {
        iterator __new_start = _M_reserve_elements_at_front(__n);
        iterator __old_start = _M_start;
        __pos = _M_start + __elemsbefore;
        __STL_TRY {
          if (__elemsbefore >= __n) {
            iterator __start_n = _M_start + __n;
            uninitialized_copy(_M_start, __start_n, __new_start);
            _M_start = __new_start;
            copy(__start_n, __pos, __old_start);
            copy(__first, __last, __pos - difference_type(__n));
          }
          else {
            const_iterator __mid = __first + (__n - __elemsbefore);
            __uninitialized_copy_copy(_M_start, __pos, __first, __mid,
                                      __new_start);
            _M_start = __new_start;
            copy(__mid, __last, __old_start);
          }
        }
        __STL_UNWIND(_M_destroy_nodes(__new_start._M_node, _M_start._M_node));
      }
      else {
        iterator __new_finish = _M_reserve_elements_at_back(__n);
        iterator __old_finish = _M_finish;
        const difference_type __elemsafter = __length - __elemsbefore;
        __pos = _M_finish - __elemsafter;
        __STL_TRY {
          if (__elemsafter > __n) {
            iterator __finish_n = _M_finish - difference_type(__n);
            uninitialized_copy(__finish_n, _M_finish, _M_finish);
            _M_finish = __new_finish;
            copy_backward(__pos, __finish_n, __old_finish);
            copy(__first, __last, __pos);
          }
          else {
            const_iterator __mid = __first + __elemsafter;
            __uninitialized_copy_copy(__mid, __last, __pos, _M_finish, _M_finish);
            _M_finish = __new_finish;
            copy(__first, __mid, __pos);
          }
        }
        __STL_UNWIND(_M_destroy_nodes(_M_finish._M_node + 1, 
                     __new_finish._M_node + 1));
      }
    }
    
    #endif /* __STL_MEMBER_TEMPLATES */
    
    template <class _Tp, class _Alloc>
    void deque<_Tp,_Alloc>::_M_new_elements_at_front(size_type __new_elems)
    {
      size_type __new_nodes
          = (__new_elems + _S_buffer_size() - 1) / _S_buffer_size();
      _M_reserve_map_at_front(__new_nodes);
      size_type __i;
      __STL_TRY {
        for (__i = 1; __i <= __new_nodes; ++__i)
          *(_M_start._M_node - __i) = _M_allocate_node();
      }
    #       ifdef __STL_USE_EXCEPTIONS
      catch(...) {
        for (size_type __j = 1; __j < __i; ++__j)
          _M_deallocate_node(*(_M_start._M_node - __j));      
        throw;
      }
    #       endif /* __STL_USE_EXCEPTIONS */
    }
    
    template <class _Tp, class _Alloc>
    void deque<_Tp,_Alloc>::_M_new_elements_at_back(size_type __new_elems)
    {
      size_type __new_nodes
          = (__new_elems + _S_buffer_size() - 1) / _S_buffer_size();
      _M_reserve_map_at_back(__new_nodes);
      size_type __i;
      __STL_TRY {
        for (__i = 1; __i <= __new_nodes; ++__i)
          *(_M_finish._M_node + __i) = _M_allocate_node();
      }
    #       ifdef __STL_USE_EXCEPTIONS
      catch(...) {
        for (size_type __j = 1; __j < __i; ++__j)
          _M_deallocate_node(*(_M_finish._M_node + __j));      
        throw;
      }
    #       endif /* __STL_USE_EXCEPTIONS */
    }
    
    template <class _Tp, class _Alloc>
    void deque<_Tp,_Alloc>::_M_reallocate_map(size_type __nodes_to_add,
                                              bool __add_at_front)
    {
      //map原始节点数
      size_type __old_num_nodes = _M_finish._M_node - _M_start._M_node + 1;
      //map新的节点数
      size_type __new_num_nodes = __old_num_nodes + __nodes_to_add;
    
      _Map_pointer __new_nstart;
      if (_M_map_size > 2 * __new_num_nodes) {//若map的大小比新节点数的两倍还大，则只需调整迭代器start和finish
        __new_nstart = _M_map + (_M_map_size - __new_num_nodes) / 2 
                         + (__add_at_front ? __nodes_to_add : 0);
        if (__new_nstart < _M_start._M_node)
          copy(_M_start._M_node, _M_finish._M_node + 1, __new_nstart);
        else
          copy_backward(_M_start._M_node, _M_finish._M_node + 1, 
                        __new_nstart + __old_num_nodes);
      }
      else {//否则需重新分配一个新的map空间
        size_type __new_map_size = 
          _M_map_size + max(_M_map_size, __nodes_to_add) + 2;
    
        _Map_pointer __new_map = _M_allocate_map(__new_map_size);
        __new_nstart = __new_map + (__new_map_size - __new_num_nodes) / 2
                             + (__add_at_front ? __nodes_to_add : 0);
        //拷贝原始map的内容
    	copy(_M_start._M_node, _M_finish._M_node + 1, __new_nstart);
    	//释放原始map空间
        _M_deallocate_map(_M_map, _M_map_size);
    	//更新map的起始地址和大小
        _M_map = __new_map;
        _M_map_size = __new_map_size;
      }
    
      //更新迭代器start和finish
      _M_start._M_set_node(__new_nstart);
      _M_finish._M_set_node(__new_nstart + __old_num_nodes - 1);
    }
    
    
    // Nonmember functions.
    
    template <class _Tp, class _Alloc>
    inline bool operator==(const deque<_Tp, _Alloc>& __x,
                           const deque<_Tp, _Alloc>& __y) {
      return __x.size() == __y.size() &&
             equal(__x.begin(), __x.end(), __y.begin());
    }
    
    template <class _Tp, class _Alloc>
    inline bool operator<(const deque<_Tp, _Alloc>& __x,
                          const deque<_Tp, _Alloc>& __y) {
      return lexicographical_compare(__x.begin(), __x.end(), 
                                     __y.begin(), __y.end());
    }
    
    #ifdef __STL_FUNCTION_TMPL_PARTIAL_ORDER
    
    template <class _Tp, class _Alloc>
    inline bool operator!=(const deque<_Tp, _Alloc>& __x,
                           const deque<_Tp, _Alloc>& __y) {
      return !(__x == __y);
    }
    
    template <class _Tp, class _Alloc>
    inline bool operator>(const deque<_Tp, _Alloc>& __x,
                          const deque<_Tp, _Alloc>& __y) {
      return __y < __x;
    }
    
    template <class _Tp, class _Alloc>
    inline bool operator<=(const deque<_Tp, _Alloc>& __x,
                           const deque<_Tp, _Alloc>& __y) {
      return !(__y < __x);
    }
    template <class _Tp, class _Alloc>
    inline bool operator>=(const deque<_Tp, _Alloc>& __x,
                           const deque<_Tp, _Alloc>& __y) {
      return !(__x < __y);
    }
    
    template <class _Tp, class _Alloc>
    inline void swap(deque<_Tp,_Alloc>& __x, deque<_Tp,_Alloc>& __y) {
      __x.swap(__y);
    }
    
    #endif /* __STL_FUNCTION_TMPL_PARTIAL_ORDER */
    
    #if defined(__sgi) && !defined(__GNUC__) && (_MIPS_SIM != _MIPS_SIM_ABI32)
    #pragma reset woff 1174
    #pragma reset woff 1375
    #endif
              
    __STL_END_NAMESPACE 
      
    #endif /* __SGI_STL_INTERNAL_DEQUE_H */
    
    // Local Variables:
    // mode:C++
    // End:

参考资料

《STL源码剖析》侯捷

[《STL源码剖析-- stl\_deque.h》][STL_-- stl_deque.h]  
 [《STL笔记之deque》][STL_deque]

[deque]: http://zh.cppreference.com/w/cpp/container/deque
[Link 1]: http://msdn.microsoft.com/zh-cn/library/22a9t119.aspx
[SouthEast]: /images/20220810/f26e78a5ab0948838253de3f3f1ee18d.png
[SouthEast 1]: /images/20220810/57ccb989ef24435d9f577aae1cee2dd9.png
[SouthEast 2]: /images/20220810/b29d0542746049279edf40cb2d66e2c3.png
[STL_-- stl_deque.h]: http://blog.csdn.net/mdl13412/article/details/6647409
[STL_deque]: http://www.programlife.net/stl-deque.html