概要

vector是stl最常用的顺序容器, 使用简单, 动态扩展, 随机访问, 在stg-stl framework下, 代码简洁

结构

整体结构

重要函数

构造析构

explicit vector(size_type __n)
    : _Base(__n, allocator_type())   // allocate n*sizeof(Tp)
    { _M_finish = uninitialized_fill_n(_M_start, __n, _Tp()); // stl_uninitialized }

 vector(const vector<_Tp, _Alloc>& __x) 
    : _Base(__x.size(), __x.get_allocator())
    { _M_finish = uninitialized_copy(__x.begin(), __x.end(), _M_start); }
~vector() { destroy(_M_start, _M_finish); } // stl_uninitialized 析构foreach call, ~_Vector_base() { _M_deallocate(_M_start, _M_end_of_storage - _M_start); } 归还到内存池

iter

  iterator begin() { return _M_start; }
  const_iterator begin() const { return _M_start; }
  iterator end() { return _M_finish; }
  const_iterator end() const { return _M_finish; }

  reverse_iterator rbegin()
    { return reverse_iterator(end()); }
  const_reverse_iterator rbegin() const
    { return const_reverse_iterator(end()); }
  reverse_iterator rend()
    { return reverse_iterator(begin()); }
  const_reverse_iterator rend() const
    { return const_reverse_iterator(begin()); }

  size_type size() const
    { return size_type(end() - begin()); }
  size_type max_size() const
    { return size_type(-1) / sizeof(_Tp); }
  size_type capacity() const
    { return size_type(_M_end_of_storage - begin()); }
  bool empty() const
    { return begin() == end(); }

  reference operator[](size_type __n) { return *(begin() + __n); }
  const_reference operator[](size_type __n) const { return *(begin() + __n); }

重要internal函数

  iterator _M_allocate_and_copy(size_type __n, const_iterator __first, 
                                               const_iterator __last)
  {
    iterator __result = _M_allocate(__n); // allocate __n*sizeof(Tp)
    __STL_TRY {
      uninitialized_copy(__first, __last, __result); // stl_uninitialized
      return __result;
    }
    __STL_UNWIND(_M_deallocate(__result, __n));
  }

template <class _Tp, class _Alloc>
void vector<_Tp, _Alloc>::_M_fill_assign(size_t __n, const value_type& __val) 
{
  if (__n > capacity()) {
    vector<_Tp, _Alloc> __tmp(__n, __val, get_allocator()); //reuse constructor, construct new one, old is not affected if allocate failed 
    __tmp.swap(*this);
  }
  else if (__n > size()) { //current capacity holds __n element
    fill(begin(), end(), __val); //stl_algo
    _M_finish = uninitialized_fill_n(_M_finish, __n - size(), __val); //stl_uninitialized cp rest
  }
  else
    erase(fill_n(begin(), __n, __val), end()); // brilliant & concise, fill front, erase rest
}

template <class _Tp, class _Alloc>
void 
vector<_Tp, _Alloc>::_M_insert_aux(iterator __position, const _Tp& __x)
{
  if (_M_finish != _M_end_of_storage) { //current capacity holds
    construct(_M_finish, *(_M_finish - 1)); //construct old finish
    ++_M_finish;
    _Tp __x_copy = __x;
    copy_backward(__position, _M_finish - 2, _M_finish - 1); // [p, old finish] ->[p + 1, old finish]
    *__position = __x_copy;
  }
  else {
    const size_type __old_size = size();
    const size_type __len = __old_size != 0 ? 2 * __old_size : 1; // double size
    iterator __new_start = _M_allocate(__len); 
    iterator __new_finish = __new_start;
    __STL_TRY {
      __new_finish = uninitialized_copy(_M_start, __position, __new_start); // cp front
      construct(__new_finish, __x); // construct @ p
      ++__new_finish;
      __new_finish = uninitialized_copy(__position, _M_finish, __new_finish); // cp rest
    }
    __STL_UNWIND((destroy(__new_start,__new_finish), 
                  _M_deallocate(__new_start,__len)));
    destroy(begin(), end());
    _M_deallocate(_M_start, _M_end_of_storage - _M_start);
    _M_start = __new_start;
    _M_finish = __new_finish;
    _M_end_of_storage = __new_start + __len;
  }
}

template <class _Tp, class _Alloc>
void vector<_Tp, _Alloc>::_M_fill_insert(iterator __position, size_type __n, 
                                         const _Tp& __x)
{
  if (__n != 0) {
    if (size_type(_M_end_of_storage - _M_finish) >= __n) { //capacity holds __element see image explanation
      _Tp __x_copy = __x;
      const size_type __elems_after = _M_finish - __position;
      iterator __old_finish = _M_finish;
      if (__elems_after > __n) { 
        uninitialized_copy(_M_finish - __n, _M_finish, _M_finish);
        _M_finish += __n;
        copy_backward(__position, __old_finish - __n, __old_finish);
        fill(__position, __position + __n, __x_copy);
      }
      else { 
        uninitialized_fill_n(_M_finish, __n - __elems_after, __x_copy);
        _M_finish += __n - __elems_after;
        uninitialized_copy(__position, __old_finish, _M_finish);  
        _M_finish += __elems_after;
        fill(__position, __old_finish, __x_copy);
      }
    }
    else { //capacity can not n
      const size_type __old_size = size();        
      const size_type __len = __old_size + max(__old_size, __n);
      iterator __new_start = _M_allocate(__len);
      iterator __new_finish = __new_start;
      __STL_TRY {
        __new_finish = uninitialized_copy(_M_start, __position, __new_start);
        __new_finish = uninitialized_fill_n(__new_finish, __n, __x);
        __new_finish
          = uninitialized_copy(__position, _M_finish, __new_finish);
      }
      __STL_UNWIND((destroy(__new_start,__new_finish), 
                    _M_deallocate(__new_start,__len)));
      destroy(_M_start, _M_finish);
      _M_deallocate(_M_start, _M_end_of_storage - _M_start);
      _M_start = __new_start;
      _M_finish = __new_finish;
      _M_end_of_storage = __new_start + __len;
    }
  }
}

template <class _Tp, class _Alloc>
vector<_Tp,_Alloc>& 
vector<_Tp,_Alloc>::operator=(const vector<_Tp, _Alloc>& __x) //see image explanation
{
  if (&__x != this) { 
    const size_type __xlen = __x.size();
    if (__xlen > capacity()) { 
      iterator __tmp = _M_allocate_and_copy(__xlen, __x.begin(), __x.end());
      destroy(_M_start, _M_finish);
      _M_deallocate(_M_start, _M_end_of_storage - _M_start);
      _M_start = __tmp;
      _M_end_of_storage = _M_start + __xlen;
    }
    else if (size() >= __xlen) {
      iterator __i = copy(__x.begin(), __x.end(), begin());
      destroy(__i, _M_finish);
    }
    else {
      copy(__x.begin(), __x.begin() + size(), _M_start);
      uninitialized_copy(__x.begin() + size(), __x.end(), _M_finish);
    }
    _M_finish = _M_start + __xlen;
  }
  return *this;
}
template <class _Tp, class _Alloc>
void 
vector<_Tp, _Alloc>::insert(iterator __position, 
                            const_iterator __first, 
                            const_iterator __last)
{
  if (__first != __last) {
    size_type __n = 0;
    distance(__first, __last, __n);
    if (size_type(_M_end_of_storage - _M_finish) >= __n) {
      const size_type __elems_after = _M_finish - __position;
      iterator __old_finish = _M_finish;
      if (__elems_after > __n) {
        uninitialized_copy(_M_finish - __n, _M_finish, _M_finish);
        _M_finish += __n;
        copy_backward(__position, __old_finish - __n, __old_finish);
        copy(__first, __last, __position);
      }
      else {
        uninitialized_copy(__first + __elems_after, __last, _M_finish);
        _M_finish += __n - __elems_after;
        uninitialized_copy(__position, __old_finish, _M_finish);
        _M_finish += __elems_after;
        copy(__first, __first + __elems_after, __position);
      }
    }
    else {
      const size_type __old_size = size();
      const size_type __len = __old_size + max(__old_size, __n);
      iterator __new_start = _M_allocate(__len);
      iterator __new_finish = __new_start;
      __STL_TRY {
        __new_finish = uninitialized_copy(_M_start, __position, __new_start);
        __new_finish = uninitialized_copy(__first, __last, __new_finish);
        __new_finish
          = uninitialized_copy(__position, _M_finish, __new_finish);
      }
      __STL_UNWIND((destroy(__new_start,__new_finish),
                    _M_deallocate(__new_start,__len)));
      destroy(_M_start, _M_finish);
      _M_deallocate(_M_start, _M_end_of_storage - _M_start);
      _M_start = __new_start;
      _M_finish = __new_finish;
      _M_end_of_storage = __new_start + __len;
    }
  }
}

_M_fill_insert图示

vector<_Tp, _Alloc>::insert(iterator __position,
const_iterator __first,
const_iterator __last)图示

总结

在stl_alloc, stl_uninitialized, stl_iter, stl_algo的加持下, vector的代码比较简洁和容易理解, 复用关系也非常清晰