stl-vector源码剖析

参考

STL源码剖析.pdf

STL源码剖析（批注版）.pdf

cplusplus-vector

正文

思维导图

TODO

源码

gcc-9.2.0 stl_vector.h

  
  // .......................................................
  template<typename _Tp, typename _Alloc = std::allocator<_Tp> >
    class vector : protected _Vector_base<_Tp, _Alloc>
    {

	  // .......................................................
      typedef _Vector_base<_Tp, _Alloc>			_Base;
      typedef typename _Base::_Tp_alloc_type		_Tp_alloc_type;
      typedef __gnu_cxx::__alloc_traits<_Tp_alloc_type>	_Alloc_traits;

    public:
      typedef _Tp					value_type;
      typedef typename _Base::pointer			pointer;
      typedef typename _Alloc_traits::const_pointer	const_pointer;
      typedef typename _Alloc_traits::reference		reference;
      typedef typename _Alloc_traits::const_reference	const_reference;
      typedef __gnu_cxx::__normal_iterator<pointer, vector> iterator;
      typedef __gnu_cxx::__normal_iterator<const_pointer, vector>
      const_iterator;
      typedef std::reverse_iterator<const_iterator>	const_reverse_iterator;
      typedef std::reverse_iterator<iterator>		reverse_iterator;
      typedef size_t					size_type;
      typedef ptrdiff_t					difference_type;
      typedef _Alloc					allocator_type;

    private:
	// C++11
	// .......................................................

    protected:
      using _Base::_M_allocate;
      using _Base::_M_deallocate;
      using _Base::_M_impl;
      using _Base::_M_get_Tp_allocator;

    public:
      // [23.2.4.1] construct/copy/destroy
      // (assign() and get_allocator() are also listed in this section)
	  //无参构造
#if __cplusplus >= 201103L
      vector() = default;
#else
      vector() { }
#endif

      /**
       *  @brief  Creates a %vector with no elements.
       *  @param  __a  An allocator object.
       */
      explicit
      vector(const allocator_type& __a) _GLIBCXX_NOEXCEPT
      : _Base(__a) { }

	  //有参构造，vector(n, m) n个元素，每个元素的值是m
#if __cplusplus >= 201103L
 	  // C++11
	  // .......................................................
#else
      /**
       *  @brief  Creates a %vector with copies of an exemplar element.
       *  @param  __n  The number of elements to initially create.
       *  @param  __value  An element to copy.
       *  @param  __a  An allocator.
       */
      explicit
      vector(size_type __n, const value_type& __value = value_type(),
	     const allocator_type& __a = allocator_type())
      : _Base(_S_check_init_len(__n, __a), __a)
      { _M_fill_initialize(__n, __value); }
#endif

	  //拷贝构造
      /**
       *  @brief  %Vector copy constructor.
       *  @param  __x  A %vector of identical element and allocator types.
       *
       *  All the elements of @a __x are copied, but any unused capacity in
       *  @a __x  will not be copied
       *  (i.e. capacity() == size() in the new %vector).
       *
       *  The newly-created %vector uses a copy of the allocator object used
       *  by @a __x (unless the allocator traits dictate a different object).
       */
      vector(const vector& __x)
      : _Base(__x.size(),
	_Alloc_traits::_S_select_on_copy(__x._M_get_Tp_allocator()))
      {
	this->_M_impl._M_finish =
	  std::__uninitialized_copy_a(__x.begin(), __x.end(),
				      this->_M_impl._M_start,
				      _M_get_Tp_allocator());
      }

#if __cplusplus >= 201103L
      // C++11
	  // .......................................................
#endif

	  //接收范围参数的构造函数
      /**
       *  @brief  Builds a %vector from a range.
       *  @param  __first  An input iterator.
       *  @param  __last  An input iterator.
       *  @param  __a  An allocator.
       *
       *  Create a %vector consisting of copies of the elements from
       *  [first,last).
       *
       *  If the iterators are forward, bidirectional, or
       *  random-access, then this will call the elements' copy
       *  constructor N times (where N is distance(first,last)) and do
       *  no memory reallocation.  But if only input iterators are
       *  used, then this will do at most 2N calls to the copy
       *  constructor, and logN memory reallocations.
       */
#if __cplusplus >= 201103L
     // C++11
	 // .......................................................
#else
      template<typename _InputIterator>
	vector(_InputIterator __first, _InputIterator __last,
	       const allocator_type& __a = allocator_type())
	: _Base(__a)
	{
	  // Check whether it's an integral type.  If so, it's not an iterator.
	  typedef typename std::__is_integer<_InputIterator>::__type _Integral;
	  _M_initialize_dispatch(__first, __last, _Integral());
	}
#endif

      /**
       *  The dtor only erases the elements, and note that if the
       *  elements themselves are pointers, the pointed-to memory is
       *  not touched in any way.  Managing the pointer is the user's
       *  responsibility.
       */
	  //_Destroy仅擦除元素，并请注意，如果元素本身是指针，则不会以任何方式访问指向的内存
	  //管理指针是用户的责任
      ~vector() _GLIBCXX_NOEXCEPT
      {
	std::_Destroy(this->_M_impl._M_start, this->_M_impl._M_finish,
		      _M_get_Tp_allocator());
	_GLIBCXX_ASAN_ANNOTATE_BEFORE_DEALLOC;
      }

	  //运算符重载，=
      /**
       *  @brief  %Vector assignment operator.
       *  @param  __x  A %vector of identical element and allocator types.
       *
       *  All the elements of @a __x are copied, but any unused capacity in
       *  @a __x will not be copied.
       *
       *  Whether the allocator is copied depends on the allocator traits.
       */
      vector&
      operator=(const vector& __x);

#if __cplusplus >= 201103L
      // C++11
	  // .......................................................
#endif

	  //assign函数，具体见下文
	  //给vector分配__n个元素，每个元素的值为__val
      void
      assign(size_type __n, const value_type& __val)
      { _M_fill_assign(__n, __val); }

	  //把模板类型的__first到__last范围的值复制给vector
#if __cplusplus >= 201103L
      // C++11
	  // .......................................................
#else
      template<typename _InputIterator>
	void
	assign(_InputIterator __first, _InputIterator __last)
	{
	  // Check whether it's an integral type.  If so, it's not an iterator.
	  typedef typename std::__is_integer<_InputIterator>::__type _Integral;
	  _M_assign_dispatch(__first, __last, _Integral());
	}
#endif

#if __cplusplus >= 201103L
      // C++11
	  // .......................................................
#endif

      /// Get a copy of the memory allocation object.
      using _Base::get_allocator;

      // iterators
      /**
       *  Returns a read/write iterator that points to the first
       *  element in the %vector.  Iteration is done in ordinary
       *  element order.
       */
      iterator
      begin() _GLIBCXX_NOEXCEPT
      { return iterator(this->_M_impl._M_start); }

      /**
       *  Returns a read-only (constant) iterator that points to the
       *  first element in the %vector.  Iteration is done in ordinary
       *  element order.
       */
      const_iterator
      begin() const _GLIBCXX_NOEXCEPT
      { return const_iterator(this->_M_impl._M_start); }

      /**
       *  Returns a read/write iterator that points one past the last
       *  element in the %vector.  Iteration is done in ordinary
       *  element order.
       */
      iterator
      end() _GLIBCXX_NOEXCEPT
      { return iterator(this->_M_impl._M_finish); }

      /**
       *  Returns a read-only (constant) iterator that points one past
       *  the last element in the %vector.  Iteration is done in
       *  ordinary element order.
       */
      const_iterator
      end() const _GLIBCXX_NOEXCEPT
      { return const_iterator(this->_M_impl._M_finish); }

      /**
       *  Returns a read/write reverse iterator that points to the
       *  last element in the %vector.  Iteration is done in reverse
       *  element order.
       */
      reverse_iterator
      rbegin() _GLIBCXX_NOEXCEPT
      { return reverse_iterator(end()); }

      /**
       *  Returns a read-only (constant) reverse iterator that points
       *  to the last element in the %vector.  Iteration is done in
       *  reverse element order.
       */
      const_reverse_iterator
      rbegin() const _GLIBCXX_NOEXCEPT
      { return const_reverse_iterator(end()); }

      /**
       *  Returns a read/write reverse iterator that points to one
       *  before the first element in the %vector.  Iteration is done
       *  in reverse element order.
       */
      reverse_iterator
      rend() _GLIBCXX_NOEXCEPT
      { return reverse_iterator(begin()); }

      /**
       *  Returns a read-only (constant) reverse iterator that points
       *  to one before the first element in the %vector.  Iteration
       *  is done in reverse element order.
       */
      const_reverse_iterator
      rend() const _GLIBCXX_NOEXCEPT
      { return const_reverse_iterator(begin()); }

#if __cplusplus >= 201103L
      /**
       *  Returns a read-only (constant) iterator that points to the
       *  first element in the %vector.  Iteration is done in ordinary
       *  element order.
       */
      const_iterator
      cbegin() const noexcept
      { return const_iterator(this->_M_impl._M_start); }

      /**
       *  Returns a read-only (constant) iterator that points one past
       *  the last element in the %vector.  Iteration is done in
       *  ordinary element order.
       */
      const_iterator
      cend() const noexcept
      { return const_iterator(this->_M_impl._M_finish); }

      /**
       *  Returns a read-only (constant) reverse iterator that points
       *  to the last element in the %vector.  Iteration is done in
       *  reverse element order.
       */
      const_reverse_iterator
      crbegin() const noexcept
      { return const_reverse_iterator(end()); }

      /**
       *  Returns a read-only (constant) reverse iterator that points
       *  to one before the first element in the %vector.  Iteration
       *  is done in reverse element order.
       */
      const_reverse_iterator
      crend() const noexcept
      { return const_reverse_iterator(begin()); }
#endif

      // [23.2.4.2] capacity
      /**  Returns the number of elements in the %vector.  */
      size_type
      size() const _GLIBCXX_NOEXCEPT
      { return size_type(this->_M_impl._M_finish - this->_M_impl._M_start); }

      /**  Returns the size() of the largest possible %vector.  */
      size_type
      max_size() const _GLIBCXX_NOEXCEPT
      { return _S_max_size(_M_get_Tp_allocator()); }

#if __cplusplus >= 201103L
      /**
       *  @brief  Resizes the %vector to the specified number of elements.
       *  @param  __new_size  Number of elements the %vector should contain.
       *
       *  This function will %resize the %vector to the specified
       *  number of elements.  If the number is smaller than the
       *  %vector's current size the %vector is truncated, otherwise
       *  default constructed elements are appended.
       */
      void
      resize(size_type __new_size)
      {
	if (__new_size > size())
	  _M_default_append(__new_size - size());
	else if (__new_size < size())
	  _M_erase_at_end(this->_M_impl._M_start + __new_size);
      }

      /**
       *  @brief  Resizes the %vector to the specified number of elements.
       *  @param  __new_size  Number of elements the %vector should contain.
       *  @param  __x  Data with which new elements should be populated.
       *
       *  This function will %resize the %vector to the specified
       *  number of elements.  If the number is smaller than the
       *  %vector's current size the %vector is truncated, otherwise
       *  the %vector is extended and new elements are populated with
       *  given data.
       */
      void
      resize(size_type __new_size, const value_type& __x)
      {
	if (__new_size > size())
	  _M_fill_insert(end(), __new_size - size(), __x);
	else if (__new_size < size())
	  _M_erase_at_end(this->_M_impl._M_start + __new_size);
      }
#else
      /**
       *  @brief  Resizes the %vector to the specified number of elements.
       *  @param  __new_size  Number of elements the %vector should contain.
       *  @param  __x  Data with which new elements should be populated.
       *
       *  This function will %resize the %vector to the specified
       *  number of elements.  If the number is smaller than the
       *  %vector's current size the %vector is truncated, otherwise
       *  the %vector is extended and new elements are populated with
       *  given data.
       */
      void
      resize(size_type __new_size, value_type __x = value_type())
      {
	if (__new_size > size())
	  _M_fill_insert(end(), __new_size - size(), __x);
	else if (__new_size < size())
	  _M_erase_at_end(this->_M_impl._M_start + __new_size);
      }
#endif

#if __cplusplus >= 201103L
      /**  A non-binding request to reduce capacity() to size().  */
      void
      shrink_to_fit()
      { _M_shrink_to_fit(); }
#endif

      /**
       *  Returns the total number of elements that the %vector can
       *  hold before needing to allocate more memory.
       */
      size_type
      capacity() const _GLIBCXX_NOEXCEPT
      { return size_type(this->_M_impl._M_end_of_storage
			 - this->_M_impl._M_start); }

      /**
       *  Returns true if the %vector is empty.  (Thus begin() would
       *  equal end().)
       */
      _GLIBCXX_NODISCARD bool
      empty() const _GLIBCXX_NOEXCEPT
      { return begin() == end(); }

      /**
       *  @brief  Attempt to preallocate enough memory for specified number of
       *          elements.
       *  @param  __n  Number of elements required.
       *  @throw  std::length_error  If @a n exceeds @c max_size().
       *
       *  This function attempts to reserve enough memory for the
       *  %vector to hold the specified number of elements.  If the
       *  number requested is more than max_size(), length_error is
       *  thrown.
       *
       *  The advantage of this function is that if optimal code is a
       *  necessity and the user can determine the number of elements
       *  that will be required, the user can reserve the memory in
       *  %advance, and thus prevent a possible reallocation of memory
       *  and copying of %vector data.
       */
      void
      reserve(size_type __n);

      // element access
      /**
       *  @brief  Subscript access to the data contained in the %vector.
       *  @param __n The index of the element for which data should be
       *  accessed.
       *  @return  Read/write reference to data.
       *
       *  This operator allows for easy, array-style, data access.
       *  Note that data access with this operator is unchecked and
       *  out_of_range lookups are not defined. (For checked lookups
       *  see at().)
       */
      reference
      operator[](size_type __n) _GLIBCXX_NOEXCEPT
      {
	__glibcxx_requires_subscript(__n);
	return *(this->_M_impl._M_start + __n);
      }

      /**
       *  @brief  Subscript access to the data contained in the %vector.
       *  @param __n The index of the element for which data should be
       *  accessed.
       *  @return  Read-only (constant) reference to data.
       *
       *  This operator allows for easy, array-style, data access.
       *  Note that data access with this operator is unchecked and
       *  out_of_range lookups are not defined. (For checked lookups
       *  see at().)
       */
      const_reference
      operator[](size_type __n) const _GLIBCXX_NOEXCEPT
      {
	__glibcxx_requires_subscript(__n);
	return *(this->_M_impl._M_start + __n);
      }

    protected:
      /// Safety check used only from at().
      void
      _M_range_check(size_type __n) const
      {
	if (__n >= this->size())
	  __throw_out_of_range_fmt(__N("vector::_M_range_check: __n "
				       "(which is %zu) >= this->size() "
				       "(which is %zu)"),
				   __n, this->size());
      }

    public:
      /**
       *  @brief  Provides access to the data contained in the %vector.
       *  @param __n The index of the element for which data should be
       *  accessed.
       *  @return  Read/write reference to data.
       *  @throw  std::out_of_range  If @a __n is an invalid index.
       *
       *  This function provides for safer data access.  The parameter
       *  is first checked that it is in the range of the vector.  The
       *  function throws out_of_range if the check fails.
       */
      reference
      at(size_type __n)
      {
	_M_range_check(__n);
	return (*this)[__n];
      }

      /**
       *  @brief  Provides access to the data contained in the %vector.
       *  @param __n The index of the element for which data should be
       *  accessed.
       *  @return  Read-only (constant) reference to data.
       *  @throw  std::out_of_range  If @a __n is an invalid index.
       *
       *  This function provides for safer data access.  The parameter
       *  is first checked that it is in the range of the vector.  The
       *  function throws out_of_range if the check fails.
       */
      const_reference
      at(size_type __n) const
      {
	_M_range_check(__n);
	return (*this)[__n];
      }

      /**
       *  Returns a read/write reference to the data at the first
       *  element of the %vector.
       */
      reference
      front() _GLIBCXX_NOEXCEPT
      {
	__glibcxx_requires_nonempty();
	return *begin();
      }

      /**
       *  Returns a read-only (constant) reference to the data at the first
       *  element of the %vector.
       */
      const_reference
      front() const _GLIBCXX_NOEXCEPT
      {
	__glibcxx_requires_nonempty();
	return *begin();
      }

      /**
       *  Returns a read/write reference to the data at the last
       *  element of the %vector.
       */
      reference
      back() _GLIBCXX_NOEXCEPT
      {
	__glibcxx_requires_nonempty();
	return *(end() - 1);
      }

      /**
       *  Returns a read-only (constant) reference to the data at the
       *  last element of the %vector.
       */
      const_reference
      back() const _GLIBCXX_NOEXCEPT
      {
	__glibcxx_requires_nonempty();
	return *(end() - 1);
      }

      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // DR 464. Suggestion for new member functions in standard containers.
      // data access
      /**
       *   Returns a pointer such that [data(), data() + size()) is a valid
       *   range.  For a non-empty %vector, data() == &front().
       */
      _Tp*
      data() _GLIBCXX_NOEXCEPT
      { return _M_data_ptr(this->_M_impl._M_start); }

      const _Tp*
      data() const _GLIBCXX_NOEXCEPT
      { return _M_data_ptr(this->_M_impl._M_start); }

      // [23.2.4.3] modifiers
      /**
       *  @brief  Add data to the end of the %vector.
       *  @param  __x  Data to be added.
       *
       *  This is a typical stack operation.  The function creates an
       *  element at the end of the %vector and assigns the given data
       *  to it.  Due to the nature of a %vector this operation can be
       *  done in constant time if the %vector has preallocated space
       *  available.
       */
      void
      push_back(const value_type& __x)
      {
	if (this->_M_impl._M_finish != this->_M_impl._M_end_of_storage)
	  {
	    _GLIBCXX_ASAN_ANNOTATE_GROW(1);
	    _Alloc_traits::construct(this->_M_impl, this->_M_impl._M_finish,
				     __x);
	    ++this->_M_impl._M_finish;
	    _GLIBCXX_ASAN_ANNOTATE_GREW(1);
	  }
	else
	  _M_realloc_insert(end(), __x);
      }

#if __cplusplus >= 201103L
      void
      push_back(value_type&& __x)
      { emplace_back(std::move(__x)); }

      template<typename... _Args>
#if __cplusplus > 201402L
	reference
#else
	void
#endif
	emplace_back(_Args&&... __args);
#endif

      /**
       *  @brief  Removes last element.
       *
       *  This is a typical stack operation. It shrinks the %vector by one.
       *
       *  Note that no data is returned, and if the last element's
       *  data is needed, it should be retrieved before pop_back() is
       *  called.
       */
      void
      pop_back() _GLIBCXX_NOEXCEPT
      {
	__glibcxx_requires_nonempty();
	--this->_M_impl._M_finish;
	_Alloc_traits::destroy(this->_M_impl, this->_M_impl._M_finish);
	_GLIBCXX_ASAN_ANNOTATE_SHRINK(1);
      }

#if __cplusplus >= 201103L
      /**
       *  @brief  Inserts an object in %vector before specified iterator.
       *  @param  __position  A const_iterator into the %vector.
       *  @param  __args  Arguments.
       *  @return  An iterator that points to the inserted data.
       *
       *  This function will insert an object of type T constructed
       *  with T(std::forward<Args>(args)...) before the specified location.
       *  Note that this kind of operation could be expensive for a %vector
       *  and if it is frequently used the user should consider using
       *  std::list.
       */
      template<typename... _Args>
	iterator
	emplace(const_iterator __position, _Args&&... __args)
	{ return _M_emplace_aux(__position, std::forward<_Args>(__args)...); }

      /**
       *  @brief  Inserts given value into %vector before specified iterator.
       *  @param  __position  A const_iterator into the %vector.
       *  @param  __x  Data to be inserted.
       *  @return  An iterator that points to the inserted data.
       *
       *  This function will insert a copy of the given value before
       *  the specified location.  Note that this kind of operation
       *  could be expensive for a %vector and if it is frequently
       *  used the user should consider using std::list.
       */
      iterator
      insert(const_iterator __position, const value_type& __x);
#else
      /**
       *  @brief  Inserts given value into %vector before specified iterator.
       *  @param  __position  An iterator into the %vector.
       *  @param  __x  Data to be inserted.
       *  @return  An iterator that points to the inserted data.
       *
       *  This function will insert a copy of the given value before
       *  the specified location.  Note that this kind of operation
       *  could be expensive for a %vector and if it is frequently
       *  used the user should consider using std::list.
       */
      iterator
      insert(iterator __position, const value_type& __x);
#endif

#if __cplusplus >= 201103L
      /**
       *  @brief  Inserts given rvalue into %vector before specified iterator.
       *  @param  __position  A const_iterator into the %vector.
       *  @param  __x  Data to be inserted.
       *  @return  An iterator that points to the inserted data.
       *
       *  This function will insert a copy of the given rvalue before
       *  the specified location.  Note that this kind of operation
       *  could be expensive for a %vector and if it is frequently
       *  used the user should consider using std::list.
       */
      iterator
      insert(const_iterator __position, value_type&& __x)
      { return _M_insert_rval(__position, std::move(__x)); }

      /**
       *  @brief  Inserts an initializer_list into the %vector.
       *  @param  __position  An iterator into the %vector.
       *  @param  __l  An initializer_list.
       *
       *  This function will insert copies of the data in the
       *  initializer_list @a l into the %vector before the location
       *  specified by @a position.
       *
       *  Note that this kind of operation could be expensive for a
       *  %vector and if it is frequently used the user should
       *  consider using std::list.
       */
      iterator
      insert(const_iterator __position, initializer_list<value_type> __l)
      {
	auto __offset = __position - cbegin();
	_M_range_insert(begin() + __offset, __l.begin(), __l.end(),
			std::random_access_iterator_tag());
	return begin() + __offset;
      }
#endif

#if __cplusplus >= 201103L
      /**
       *  @brief  Inserts a number of copies of given data into the %vector.
       *  @param  __position  A const_iterator into the %vector.
       *  @param  __n  Number of elements to be inserted.
       *  @param  __x  Data to be inserted.
       *  @return  An iterator that points to the inserted data.
       *
       *  This function will insert a specified number of copies of
       *  the given data before the location specified by @a position.
       *
       *  Note that this kind of operation could be expensive for a
       *  %vector and if it is frequently used the user should
       *  consider using std::list.
       */
      iterator
      insert(const_iterator __position, size_type __n, const value_type& __x)
      {
	difference_type __offset = __position - cbegin();
	_M_fill_insert(begin() + __offset, __n, __x);
	return begin() + __offset;
      }
#else
      /**
       *  @brief  Inserts a number of copies of given data into the %vector.
       *  @param  __position  An iterator into the %vector.
       *  @param  __n  Number of elements to be inserted.
       *  @param  __x  Data to be inserted.
       *
       *  This function will insert a specified number of copies of
       *  the given data before the location specified by @a position.
       *
       *  Note that this kind of operation could be expensive for a
       *  %vector and if it is frequently used the user should
       *  consider using std::list.
       */
      void
      insert(iterator __position, size_type __n, const value_type& __x)
      { _M_fill_insert(__position, __n, __x); }
#endif

#if __cplusplus >= 201103L
      /**
       *  @brief  Inserts a range into the %vector.
       *  @param  __position  A const_iterator into the %vector.
       *  @param  __first  An input iterator.
       *  @param  __last   An input iterator.
       *  @return  An iterator that points to the inserted data.
       *
       *  This function will insert copies of the data in the range
       *  [__first,__last) into the %vector before the location specified
       *  by @a pos.
       *
       *  Note that this kind of operation could be expensive for a
       *  %vector and if it is frequently used the user should
       *  consider using std::list.
       */
      template<typename _InputIterator,
	       typename = std::_RequireInputIter<_InputIterator>>
	iterator
	insert(const_iterator __position, _InputIterator __first,
	       _InputIterator __last)
	{
	  difference_type __offset = __position - cbegin();
	  _M_insert_dispatch(begin() + __offset,
			     __first, __last, __false_type());
	  return begin() + __offset;
	}
#else
      /**
       *  @brief  Inserts a range into the %vector.
       *  @param  __position  An iterator into the %vector.
       *  @param  __first  An input iterator.
       *  @param  __last   An input iterator.
       *
       *  This function will insert copies of the data in the range
       *  [__first,__last) into the %vector before the location specified
       *  by @a pos.
       *
       *  Note that this kind of operation could be expensive for a
       *  %vector and if it is frequently used the user should
       *  consider using std::list.
       */
      template<typename _InputIterator>
	void
	insert(iterator __position, _InputIterator __first,
	       _InputIterator __last)
	{
	  // Check whether it's an integral type.  If so, it's not an iterator.
	  typedef typename std::__is_integer<_InputIterator>::__type _Integral;
	  _M_insert_dispatch(__position, __first, __last, _Integral());
	}
#endif

      /**
       *  @brief  Remove element at given position.
       *  @param  __position  Iterator pointing to element to be erased.
       *  @return  An iterator pointing to the next element (or end()).
       *
       *  This function will erase the element at the given position and thus
       *  shorten the %vector by one.
       *
       *  Note This operation could be expensive and if it is
       *  frequently used the user should consider using std::list.
       *  The user is also cautioned that this function only erases
       *  the element, and that if the element is itself a pointer,
       *  the pointed-to memory is not touched in any way.  Managing
       *  the pointer is the user's responsibility.
       */
      iterator
#if __cplusplus >= 201103L
      erase(const_iterator __position)
      { return _M_erase(begin() + (__position - cbegin())); }
#else
      erase(iterator __position)
      { return _M_erase(__position); }
#endif

      /**
       *  @brief  Remove a range of elements.
       *  @param  __first  Iterator pointing to the first element to be erased.
       *  @param  __last  Iterator pointing to one past the last element to be
       *                  erased.
       *  @return  An iterator pointing to the element pointed to by @a __last
       *           prior to erasing (or end()).
       *
       *  This function will erase the elements in the range
       *  [__first,__last) and shorten the %vector accordingly.
       *
       *  Note This operation could be expensive and if it is
       *  frequently used the user should consider using std::list.
       *  The user is also cautioned that this function only erases
       *  the elements, and that if the elements themselves are
       *  pointers, the pointed-to memory is not touched in any way.
       *  Managing the pointer is the user's responsibility.
       */
      iterator
#if __cplusplus >= 201103L
      erase(const_iterator __first, const_iterator __last)
      {
	const auto __beg = begin();
	const auto __cbeg = cbegin();
	return _M_erase(__beg + (__first - __cbeg), __beg + (__last - __cbeg));
      }
#else
      erase(iterator __first, iterator __last)
      { return _M_erase(__first, __last); }
#endif

      /**
       *  @brief  Swaps data with another %vector.
       *  @param  __x  A %vector of the same element and allocator types.
       *
       *  This exchanges the elements between two vectors in constant time.
       *  (Three pointers, so it should be quite fast.)
       *  Note that the global std::swap() function is specialized such that
       *  std::swap(v1,v2) will feed to this function.
       *
       *  Whether the allocators are swapped depends on the allocator traits.
       */
      void
      swap(vector& __x) _GLIBCXX_NOEXCEPT
      {
#if __cplusplus >= 201103L
	__glibcxx_assert(_Alloc_traits::propagate_on_container_swap::value
			 || _M_get_Tp_allocator() == __x._M_get_Tp_allocator());
#endif
	this->_M_impl._M_swap_data(__x._M_impl);
	_Alloc_traits::_S_on_swap(_M_get_Tp_allocator(),
				  __x._M_get_Tp_allocator());
      }

      /**
       *  Erases all the elements.  Note that this function only erases the
       *  elements, and that if the elements themselves are pointers, the
       *  pointed-to memory is not touched in any way.  Managing the pointer is
       *  the user's responsibility.
       */
      void
      clear() _GLIBCXX_NOEXCEPT
      { _M_erase_at_end(this->_M_impl._M_start); }

    protected:
      /**
       *  Memory expansion handler.  Uses the member allocation function to
       *  obtain @a n bytes of memory, and then copies [first,last) into it.
       */
      template<typename _ForwardIterator>
	pointer
	_M_allocate_and_copy(size_type __n,
			     _ForwardIterator __first, _ForwardIterator __last)
	{
	  pointer __result = this->_M_allocate(__n);
	  __try
	    {
	      std::__uninitialized_copy_a(__first, __last, __result,
					  _M_get_Tp_allocator());
	      return __result;
	    }
	  __catch(...)
	    {
	      _M_deallocate(__result, __n);
	      __throw_exception_again;
	    }
	}


      // Internal constructor functions follow.

      // Called by the range constructor to implement [23.1.1]/9

#if __cplusplus < 201103L
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 438. Ambiguity in the "do the right thing" clause
      template<typename _Integer>
	void
	_M_initialize_dispatch(_Integer __n, _Integer __value, __true_type)
	{
	  this->_M_impl._M_start = _M_allocate(_S_check_init_len(
		static_cast<size_type>(__n), _M_get_Tp_allocator()));
	  this->_M_impl._M_end_of_storage =
	    this->_M_impl._M_start + static_cast<size_type>(__n);
	  _M_fill_initialize(static_cast<size_type>(__n), __value);
	}

      // Called by the range constructor to implement [23.1.1]/9
      template<typename _InputIterator>
	void
	_M_initialize_dispatch(_InputIterator __first, _InputIterator __last,
			       __false_type)
	{
	  _M_range_initialize(__first, __last,
			      std::__iterator_category(__first));
	}
#endif

      // Called by the second initialize_dispatch above
      template<typename _InputIterator>
	void
	_M_range_initialize(_InputIterator __first, _InputIterator __last,
			    std::input_iterator_tag)
	{
	  __try {
	    for (; __first != __last; ++__first)
#if __cplusplus >= 201103L
	      emplace_back(*__first);
#else
	      push_back(*__first);
#endif
	  } __catch(...) {
	    clear();
	    __throw_exception_again;
	  }
	}

      // Called by the second initialize_dispatch above
      template<typename _ForwardIterator>
	void
	_M_range_initialize(_ForwardIterator __first, _ForwardIterator __last,
			    std::forward_iterator_tag)
	{
	  const size_type __n = std::distance(__first, __last);
	  this->_M_impl._M_start
	    = this->_M_allocate(_S_check_init_len(__n, _M_get_Tp_allocator()));
	  this->_M_impl._M_end_of_storage = this->_M_impl._M_start + __n;
	  this->_M_impl._M_finish =
	    std::__uninitialized_copy_a(__first, __last,
					this->_M_impl._M_start,
					_M_get_Tp_allocator());
	}

      // Called by the first initialize_dispatch above and by the
      // vector(n,value,a) constructor.
      void
      _M_fill_initialize(size_type __n, const value_type& __value)
      {
	this->_M_impl._M_finish =
	  std::__uninitialized_fill_n_a(this->_M_impl._M_start, __n, __value,
					_M_get_Tp_allocator());
      }

#if __cplusplus >= 201103L
      // Called by the vector(n) constructor.
      void
      _M_default_initialize(size_type __n)
      {
	this->_M_impl._M_finish =
	  std::__uninitialized_default_n_a(this->_M_impl._M_start, __n,
					   _M_get_Tp_allocator());
      }
#endif

      // Internal assign functions follow.  The *_aux functions do the actual
      // assignment work for the range versions.

      // Called by the range assign to implement [23.1.1]/9

      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 438. Ambiguity in the "do the right thing" clause
      template<typename _Integer>
	void
	_M_assign_dispatch(_Integer __n, _Integer __val, __true_type)
	{ _M_fill_assign(__n, __val); }

      // Called by the range assign to implement [23.1.1]/9
      template<typename _InputIterator>
	void
	_M_assign_dispatch(_InputIterator __first, _InputIterator __last,
			   __false_type)
	{ _M_assign_aux(__first, __last, std::__iterator_category(__first)); }

      // Called by the second assign_dispatch above
      template<typename _InputIterator>
	void
	_M_assign_aux(_InputIterator __first, _InputIterator __last,
		      std::input_iterator_tag);

      // Called by the second assign_dispatch above
      template<typename _ForwardIterator>
	void
	_M_assign_aux(_ForwardIterator __first, _ForwardIterator __last,
		      std::forward_iterator_tag);

      // Called by assign(n,t), and the range assign when it turns out
      // to be the same thing.
      void
      _M_fill_assign(size_type __n, const value_type& __val);

      // Internal insert functions follow.

      // Called by the range insert to implement [23.1.1]/9

      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 438. Ambiguity in the "do the right thing" clause
      template<typename _Integer>
	void
	_M_insert_dispatch(iterator __pos, _Integer __n, _Integer __val,
			   __true_type)
	{ _M_fill_insert(__pos, __n, __val); }

      // Called by the range insert to implement [23.1.1]/9
      template<typename _InputIterator>
	void
	_M_insert_dispatch(iterator __pos, _InputIterator __first,
			   _InputIterator __last, __false_type)
	{
	  _M_range_insert(__pos, __first, __last,
			  std::__iterator_category(__first));
	}

      // Called by the second insert_dispatch above
      template<typename _InputIterator>
	void
	_M_range_insert(iterator __pos, _InputIterator __first,
			_InputIterator __last, std::input_iterator_tag);

      // Called by the second insert_dispatch above
      template<typename _ForwardIterator>
	void
	_M_range_insert(iterator __pos, _ForwardIterator __first,
			_ForwardIterator __last, std::forward_iterator_tag);

      // Called by insert(p,n,x), and the range insert when it turns out to be
      // the same thing.
      void
      _M_fill_insert(iterator __pos, size_type __n, const value_type& __x);

#if __cplusplus >= 201103L
      // Called by resize(n).
      void
      _M_default_append(size_type __n);

      bool
      _M_shrink_to_fit();
#endif

#if __cplusplus < 201103L
      // Called by insert(p,x)
      void
      _M_insert_aux(iterator __position, const value_type& __x);

      void
      _M_realloc_insert(iterator __position, const value_type& __x);
#else
      // A value_type object constructed with _Alloc_traits::construct()
      // and destroyed with _Alloc_traits::destroy().
      struct _Temporary_value
      {
	template<typename... _Args>
	  explicit
	  _Temporary_value(vector* __vec, _Args&&... __args) : _M_this(__vec)
	  {
	    _Alloc_traits::construct(_M_this->_M_impl, _M_ptr(),
				     std::forward<_Args>(__args)...);
	  }

	~_Temporary_value()
	{ _Alloc_traits::destroy(_M_this->_M_impl, _M_ptr()); }

	value_type&
	_M_val() { return *_M_ptr(); }

      private:
	_Tp*
	_M_ptr() { return reinterpret_cast<_Tp*>(&__buf); }

	vector* _M_this;
	typename aligned_storage<sizeof(_Tp), alignof(_Tp)>::type __buf;
      };

      // Called by insert(p,x) and other functions when insertion needs to
      // reallocate or move existing elements. _Arg is either _Tp& or _Tp.
      template<typename _Arg>
	void
	_M_insert_aux(iterator __position, _Arg&& __arg);

      template<typename... _Args>
	void
	_M_realloc_insert(iterator __position, _Args&&... __args);

      // Either move-construct at the end, or forward to _M_insert_aux.
      iterator
      _M_insert_rval(const_iterator __position, value_type&& __v);

      // Try to emplace at the end, otherwise forward to _M_insert_aux.
      template<typename... _Args>
	iterator
	_M_emplace_aux(const_iterator __position, _Args&&... __args);

      // Emplacing an rvalue of the correct type can use _M_insert_rval.
      iterator
      _M_emplace_aux(const_iterator __position, value_type&& __v)
      { return _M_insert_rval(__position, std::move(__v)); }
#endif

      // Called by _M_fill_insert, _M_insert_aux etc.
      size_type
      _M_check_len(size_type __n, const char* __s) const
      {
	if (max_size() - size() < __n)
	  __throw_length_error(__N(__s));

	const size_type __len = size() + (std::max)(size(), __n);
	return (__len < size() || __len > max_size()) ? max_size() : __len;
      }

      // Called by constructors to check initial size.
      static size_type
      _S_check_init_len(size_type __n, const allocator_type& __a)
      {
	if (__n > _S_max_size(_Tp_alloc_type(__a)))
	  __throw_length_error(
	      __N("cannot create std::vector larger than max_size()"));
	return __n;
      }

      static size_type
      _S_max_size(const _Tp_alloc_type& __a) _GLIBCXX_NOEXCEPT
      {
	// std::distance(begin(), end()) cannot be greater than PTRDIFF_MAX,
	// and realistically we can't store more than PTRDIFF_MAX/sizeof(T)
	// (even if std::allocator_traits::max_size says we can).
	const size_t __diffmax
	  = __gnu_cxx::__numeric_traits<ptrdiff_t>::__max / sizeof(_Tp);
	const size_t __allocmax = _Alloc_traits::max_size(__a);
	return (std::min)(__diffmax, __allocmax);
      }

      // Internal erase functions follow.

      // Called by erase(q1,q2), clear(), resize(), _M_fill_assign,
      // _M_assign_aux.
      void
      _M_erase_at_end(pointer __pos) _GLIBCXX_NOEXCEPT
      {
	if (size_type __n = this->_M_impl._M_finish - __pos)
	  {
	    std::_Destroy(__pos, this->_M_impl._M_finish,
			  _M_get_Tp_allocator());
	    this->_M_impl._M_finish = __pos;
	    _GLIBCXX_ASAN_ANNOTATE_SHRINK(__n);
	  }
      }

      iterator
      _M_erase(iterator __position);

      iterator
      _M_erase(iterator __first, iterator __last);

#if __cplusplus >= 201103L
    private:
      // Constant-time move assignment when source object's memory can be
      // moved, either because the source's allocator will move too
      // or because the allocators are equal.
      void
      _M_move_assign(vector&& __x, true_type) noexcept
      {
	vector __tmp(get_allocator());
	this->_M_impl._M_swap_data(__x._M_impl);
	__tmp._M_impl._M_swap_data(__x._M_impl);
	std::__alloc_on_move(_M_get_Tp_allocator(), __x._M_get_Tp_allocator());
      }

      // Do move assignment when it might not be possible to move source
      // object's memory, resulting in a linear-time operation.
      void
      _M_move_assign(vector&& __x, false_type)
      {
	if (__x._M_get_Tp_allocator() == this->_M_get_Tp_allocator())
	  _M_move_assign(std::move(__x), true_type());
	else
	  {
	    // The rvalue's allocator cannot be moved and is not equal,
	    // so we need to individually move each element.
	    this->assign(std::__make_move_if_noexcept_iterator(__x.begin()),
			 std::__make_move_if_noexcept_iterator(__x.end()));
	    __x.clear();
	  }
      }
#endif

      template<typename _Up>
	_Up*
	_M_data_ptr(_Up* __ptr) const _GLIBCXX_NOEXCEPT
	{ return __ptr; }

#if __cplusplus >= 201103L
      template<typename _Ptr>
	typename std::pointer_traits<_Ptr>::element_type*
	_M_data_ptr(_Ptr __ptr) const
	{ return empty() ? nullptr : std::__to_address(__ptr); }
#else
      template<typename _Up>
	_Up*
	_M_data_ptr(_Up* __ptr) _GLIBCXX_NOEXCEPT
	{ return __ptr; }

      template<typename _Ptr>
	value_type*
	_M_data_ptr(_Ptr __ptr)
	{ return empty() ? (value_type*)0 : __ptr.operator->(); }

      template<typename _Ptr>
	const value_type*
	_M_data_ptr(_Ptr __ptr) const
	{ return empty() ? (const value_type*)0 : __ptr.operator->(); }
#endif
    }

---

assign

input:

#include <iostream>
#include <vector>
using namespace std;

void func_print(std::vector<int> &ovec)
{
    std::vector<int>::iterator it = ovec.begin();
    for(it; it != ovec.end(); it++)
    {
        cout << " " << *it ;
    }
    cout << endl;
    return ;
}

int main ()
{
  std::vector<int> first;
  std::vector<int> second;
  std::vector<int> third;

  first.assign (7,100);             // 7 ints with a value of 100

  std::vector<int>::iterator it;
  it=first.begin()+1;

  second.assign (it,first.end()-1); // the 5 central values of first

  int myints[] = {1776,7,4};
  third.assign (myints,myints+3);   // assigning from array.

  std::cout << "Size of first: " << int (first.size()) << '\n';
  func_print(first);
  std::cout << "Size of second: " << int (second.size()) << '\n';
  func_print(second);
  std::cout << "Size of third: " << int (third.size()) << '\n';
  func_print(third);
  return 0;
}

output:

Size of first: 7
 100 100 100 100 100 100 100
Size of second: 5
 100 100 100 100 100
Size of third: 3
 1776 7 4

Process returned 0 (0x0)   execution time : 0.015 s
Press any key to continue.

总结

assgin有2个实现：

void assign (InputIterator first, InputIterator last);

void assign (size_type n, const value_type& val);

带范围的assign的最后一个参数是不会被复制的，

如first = it, last = it + 5, 则一共复制5个值

it, it+1, it+2, it+3, it+4

end()函数是vector最后一个元素的后一个元素，一般值为0

cout打印iterator的地址： &*it

---

push_bask()

void push_back (const value_type& val);

Adds a new element at the end of the vector, after its current last element. The content of val is copied (or moved) to the new element.

This effectively increases the container size by one, which causes an automatic reallocation of the allocated storage space if -and only if- the new vector size surpasses the current vector capacity.

void
  push_back(const value_type& __x)
  {
if (this->_M_impl._M_finish != this->_M_impl._M_end_of_storage)
  {
    _GLIBCXX_ASAN_ANNOTATE_GROW(1);
    _Alloc_traits::construct(this->_M_impl, this->_M_impl._M_finish,
                 __x);
    ++this->_M_impl._M_finish;
    _GLIBCXX_ASAN_ANNOTATE_GREW(1);
  }
else
  _M_realloc_insert(end(), __x);
  }

扩容实现见下文空间配置实现

pop_back()

void pop_back（）;

Removes the last element in the vector, effectively reducing the container size by one.

This destroys the removed element.

void
  pop_back() _GLIBCXX_NOEXCEPT
  {
__glibcxx_requires_nonempty();
--this->_M_impl._M_finish;
_Alloc_traits::destroy(this->_M_impl, this->_M_impl._M_finish);
_GLIBCXX_ASAN_ANNOTATE_SHRINK(1);
  }

从最后删除一个元素，这并不会导致vector的总容量变化

size()

size_type size() const;

Returns the number of elements in the vector.

This is the number of actual objects held in the vector, which is not necessarily equal to its storage capacity.

size_type
  size() const _GLIBCXX_NOEXCEPT
  { return size_type(this->_M_impl._M_finish - this->_M_impl._M_start); }

begin()

iterator begin(); const_iterator begin() const;

Returns an iterator pointing to the first element in the vector.

Notice that, unlike member vector::front, which returns a reference to the first element, this function returns a random access iterator pointing to it.

If the container is empty, the returned iterator value shall not be dereferenced.

iterator
  begin() _GLIBCXX_NOEXCEPT
  { return iterator(this->_M_impl._M_start); }


const_iterator
  begin() const _GLIBCXX_NOEXCEPT
  { return const_iterator(this->_M_impl._M_start); }

front()

reference front(); const_reference front() const;

Access first element
Returns a reference to the first element in the vector.

Unlike member vector::begin, which returns an iterator to this same element, this function returns a direct reference.

Calling this function on an empty container causes undefined behavior.

reference
  front() _GLIBCXX_NOEXCEPT
  {
__glibcxx_requires_nonempty();
return *begin();
  }

const_reference
  front() const _GLIBCXX_NOEXCEPT
  {
__glibcxx_requires_nonempty();
return *begin();
  }

front返回的是*begin(),是引用

back()

reference back(); const_reference back() const;

Returns a reference to the last element in the vector.

reference
  back() _GLIBCXX_NOEXCEPT
  {
__glibcxx_requires_nonempty();
return *(end() - 1);
  }

 const_reference
  back() const _GLIBCXX_NOEXCEPT
  {
__glibcxx_requires_nonempty();
return *(end() - 1);

back返回最后一个值，返回值是reference

end返回最后一个元素的下一个元素，是iterator

end()

iterator end(); const_iterator end() const;

Returns an iterator referring to the past-the-end element in the vector container.

iterator
  end() _GLIBCXX_NOEXCEPT
  { return iterator(this->_M_impl._M_finish); }

const_iterator
  end() const _GLIBCXX_NOEXCEPT
  { return const_iterator(this->_M_impl._M_finish); }

rbegin()

const_iterator cbegin() const noexcept;

Return const_iterator to beginning

reverse_iterator
  rbegin() _GLIBCXX_NOEXCEPT
  { return reverse_iterator(end()); }

const_reverse_iterator
  rbegin() const _GLIBCXX_NOEXCEPT
  { return const_reverse_iterator(end()); }

rend()

TODO

---

空间配置原则

template<typename _Tp, typename _Alloc = std::allocator<_Tp> >
class vector : protected _Vector_base<_Tp, _Alloc>
{
    ...
}

template<typename _Tp, typename _Alloc>
struct _Vector_base
{

    struct _Vector_impl_data
      {
        pointer _M_start;                //表示目前使用空间的头
        pointer _M_finish;                //表示目前使用空间的尾
        pointer _M_end_of_storage;        //表示目前可用空间的尾
        ...
      }

}

input

#include <iostream>
#include <vector>
using namespace std;

int main()
{
	std::vector<int> vec ;
	vec.push_back(8);
	vec.push_back(6);
	vec.push_back(7);
	vec.end();


}

/* stl_vector.h  gcc 4.8.5 c++ 98
900	  void
901		   push_back(const value_type& __x)
902		   {
903		 if (this->_M_impl._M_finish != this->_M_impl._M_end_of_storage)
904		   {
905		 	 _Alloc_traits::construct(this->_M_impl, this->_M_impl._M_finish,
906									  __x);
907			 ++this->_M_impl._M_finish;
908		   }
909		 else
910	 #if __cplusplus >= 201103L
911		   _M_emplace_back_aux(__x);
912	 #else
913		   _M_insert_aux(end(), __x);
914	 #endif
915		   }

*/

output

Breakpoint 5, std::vector<int, std::allocator<int> >::push_back (this=0x7fffffffe220, __x=@0x7fffffffe244: 8) at /usr/include/c++/4.8.2/bits/stl_vector.h:915
915          }
(gdb) p (this->_M_impl._M_start)
$17 = (std::_Vector_base<int, std::allocator<int> >::pointer) 0x604010
(gdb) p (this->_M_impl._M_finish)
$18 = (std::_Vector_base<int, std::allocator<int> >::pointer) 0x604014
(gdb) p (this->_M_impl._M_end_of_storage)
$19 = (std::_Vector_base<int, std::allocator<int> >::pointer) 0x604014
(gdb) p (this->_M_impl._M_end_of_storage-this->_M_impl._M_start)
$20 = 1
(gdb) p *(this->_M_impl._M_start)
$21 = 8
(gdb) c
Continuing.

Breakpoint 4, std::vector<int, std::allocator<int> >::push_back (this=0x7fffffffe220, __x=@0x7fffffffe248: 6) at /usr/include/c++/4.8.2/bits/stl_vector.h:903
903        if (this->_M_impl._M_finish != this->_M_impl._M_end_of_storage)
(gdb) c
Continuing.

Breakpoint 5, std::vector<int, std::allocator<int> >::push_back (this=0x7fffffffe220, __x=@0x7fffffffe248: 6) at /usr/include/c++/4.8.2/bits/stl_vector.h:915
915          }
(gdb) p (this->_M_impl._M_start)
$22 = (std::_Vector_base<int, std::allocator<int> >::pointer) 0x604030
(gdb) p (this->_M_impl._M_finish)
$23 = (std::_Vector_base<int, std::allocator<int> >::pointer) 0x604038
(gdb) p (this->_M_impl._M_end_of_storage)
$24 = (std::_Vector_base<int, std::allocator<int> >::pointer) 0x604038
(gdb) p (this->_M_impl._M_end_of_storage-this->_M_impl._M_start)
$25 = 2
(gdb) p *(this->_M_impl._M_start)
$26 = 8
(gdb) p *(this->_M_impl._M_start+1)
$27 = 6
(gdb) p (this->_M_impl._M_start+1)
$28 = (int *) 0x604034
(gdb) c
Continuing.

Breakpoint 4, std::vector<int, std::allocator<int> >::push_back (this=0x7fffffffe220, __x=@0x7fffffffe24c: 7) at /usr/include/c++/4.8.2/bits/stl_vector.h:903
903        if (this->_M_impl._M_finish != this->_M_impl._M_end_of_storage)
(gdb) c
Continuing.

Breakpoint 5, std::vector<int, std::allocator<int> >::push_back (this=0x7fffffffe220, __x=@0x7fffffffe24c: 7) at /usr/include/c++/4.8.2/bits/stl_vector.h:915
915          }
(gdb) p (this->_M_impl._M_start)
$29 = (std::_Vector_base<int, std::allocator<int> >::pointer) 0x604010
(gdb) p (this->_M_impl._M_finish)
$30 = (std::_Vector_base<int, std::allocator<int> >::pointer) 0x60401c
(gdb) p (this->_M_impl._M_end_of_storage-this->_M_impl._M_start)
$31 = 4
(gdb) p (this->_M_impl._M_end_of_storage)
$32 = (std::_Vector_base<int, std::allocator<int> >::pointer) 0x604020
(gdb) p *(this->_M_impl._M_start+2)
$33 = 7
(gdb) p (this->_M_impl._M_start+2)
$34 = (int *) 0x604018
(gdb) q

空间配置实现

//*******************vector constructor
explicit
  vector(size_type __n, const value_type& __value = value_type(),
     const allocator_type& __a = allocator_type())
  : _Base(_S_check_init_len(__n, __a), __a)
  { _M_fill_initialize(__n, __value); }


  //*******************_M_fill_initialize
  // Called by the first initialize_dispatch above and by the
  // vector(n,value,a) constructor.
  void
  _M_fill_initialize(size_type __n, const value_type& __value)
  {
this->_M_impl._M_finish =
  std::__uninitialized_fill_n_a(this->_M_impl._M_start, __n, __value,
                _M_get_Tp_allocator());
  }

//*******************__uninitialized_fill_n_a
//__uninitialized_fill_n_a会根据第一参数的型别特性（type traits），
//决定使用算法 fill_n()或反复呼叫 construct() 来完成任务
template<typename _ForwardIterator, typename _Size, typename _Tp,
   typename _Allocator>
_ForwardIterator
__uninitialized_fill_n_a(_ForwardIterator __first, _Size __n, 
             const _Tp& __x, _Allocator& __alloc)
{
  _ForwardIterator __cur = __first;
  __try
{
  typedef __gnu_cxx::__alloc_traits<_Allocator> __traits;
  for (; __n > 0; --__n, (void) ++__cur)
    __traits::construct(__alloc, std::__addressof(*__cur), __x);
  return __cur;
}
  __catch(...)
{
  std::_Destroy(__first, __cur, __alloc);
  __throw_exception_again;
}
}

//__uninitialized_fill_n_a使用uninitialized_fill_n
template<typename _ForwardIterator, typename _Size, typename _Tp,
   typename _Tp2>
inline _ForwardIterator
__uninitialized_fill_n_a(_ForwardIterator __first, _Size __n, 
             const _Tp& __x, allocator<_Tp2>&)
{ return std::uninitialized_fill_n(__first, __n, __x); }

constructor 与 ++ –

ending