STL剖析笔记

Posted 刘二毛

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序列式容器

元素可序,但未必有序。

vector

vector的数据结构与array相似,不同在于array是静态空间,一旦配置了内存空间就不能改变,如果要更换内存大小,需要配置一个新空间,然后将元素从旧地址一一搬到新地址,再把原来的旧空间释放。而vector是动态空间,新加入元素时,会自动扩充空间以容纳新元素。

vector源码

// 默认allocator为alloc, 其具体使用版本请参照<stl_alloc.h>    
template <class T, class Alloc = alloc>    
class vector    
    
public:    
  // 标记为'STL标准强制要求'的typedefs用于提供iterator_traits<I>支持    
  typedef T value_type;                         // STL标准强制要求    
  typedef value_type* pointer;                  // STL标准强制要求    
  typedef const value_type* const_pointer;    
  // 由于vector的特性, 一般我们实作的时候都分配给其连续的内存空间,    
  // 所以其迭代器只需要定义成原生指针即可满足需要    
  typedef value_type* iterator;                 // STL标准强制要求    
  typedef const value_type* const_iterator;    
  typedef value_type& reference;                // STL标准强制要求    
  typedef const value_type& const_reference;    
  typedef size_t size_type;    
  typedef ptrdiff_t difference_type;            // STL标准强制要求    
    
#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:    
  // 这个提供STL标准的allocator接口    
  typedef simple_alloc<value_type, Alloc> data_allocator;    
    
  iterator start;               // 内存空间起始点    
  iterator finish;              // 当前使用的内存空间结束点    
  iterator end_of_storage;      // 实际分配内存空间的结束点    
    
  void insert_aux(iterator position, const T& x);    
    
  // 释放分配的内存空间    
  void deallocate()    
      
    // 由于使用的是data_allocator进行内存空间的分配,    
    // 所以需要同样嗲用data_allocator::deallocate()进行释放    
    // 如果直接释放, 对于data_allocator内部使用内存池的版本    
    // 就会发生错误    
    if (start) data_allocator::deallocate(start, end_of_storage - start);    
      
    
  void fill_initialize(size_type n, const T& value)    
      
    start = allocate_and_fill(n, value);    
    finish = start + n;                         // 设置当前使用内存空间的结束点    
    // 构造阶段, 此实作不多分配内存,    
    // 所以要设置内存空间结束点和, 已经使用的内存空间结束点相同    
    end_of_storage = finish;    
      
    
public:    
  // 获取几种迭代器    
  iterator begin()  return start;     
  const_iterator begin() const  return start;     
  iterator end()  return finish;     
  const_iterator end() const  return 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());    
      
    
  // 返回当前对象个数    
  size_type size() const  return size_type(end() - begin());     
  size_type max_size() const  return size_type(-1) / sizeof(T);     
  // 返回重新分配内存前最多能存储的对象个数    
  size_type capacity() const  return size_type(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);     
    
  // 本实作中默认构造出的vector不分配内存空间    
  vector() : start(0), finish(0), end_of_storage(0)     
    
    
// 本实作中给定个数和对象, 则只分配所需内存, 不会多分配    
    
//                    vector(size_type n, const T& value)    
//                                   ↓    
//                         fill_initialize(n, value)    
//                                   ↓    
//                        allocate_and_fill(n, value)    
//                                   ↓    
//          data_allocator::allocate(n)          <stl_alloc.h>    
//          uninitialized_fill_n(result, n, x)  <stl_uninitialized.h>    
    
    
  vector(size_type n, const T& value)  fill_initialize(n, value);     
  vector(int n, const T& value)  fill_initialize(n, value);     
  vector(long n, const T& value)  fill_initialize(n, value);     
    
  // 需要对象提供默认构造函数    
  explicit vector(size_type n)  fill_initialize(n, T());     
    
    
// 复制构造, 同样不会多分配内存    
    
//                     vector(const vector<T, Alloc>& x)    
//                                   ↓    
//         allocate_and_copy(x.end() - x.begin(), x.begin(), x.end());    
//                                   ↓    
//        data_allocator::allocate(n)              <stl_alloc.h>    
//        uninitialized_copy(first, last, result); <stl_uninitialized.h>    
    
    
  vector(const vector<T, Alloc>& x)    
      
    start = allocate_and_copy(x.end() - x.begin(), x.begin(), x.end());    
    finish = start + (x.end() - x.begin());    
    end_of_storage = finish;    
      
    
// 复制指定区间的元素, 同样不多分配内存    
#ifdef __STL_MEMBER_TEMPLATES    
    
// 复制一个区间进行构造, 可能会导致多分配内存    
    
//               vector(InputIterator first, InputIterator last)    
//                                   ↓    
//            range_initialize(first, last, iterator_category(first));    
//                                   ↓    
//                     for ( ; first != last; ++first)    
//                         push_back(*first);    
//            由于使用push_back()操作, 可能导致多次重复分配内存,个人感觉应该先    
//            data_allocator::allocate((last - first) * sizeof(T));    
//            然后uninitialized_copy(first, last, result);    
//            这样不会多分配内存, 也不会导致多次重新分配内存问题    
    
    
  template <class InputIterator>    
  vector(InputIterator first, InputIterator last) :    
    start(0), finish(0), end_of_storage(0)    
      
    range_initialize(first, last, iterator_category(first));    
      
#else /* __STL_MEMBER_TEMPLATES */    
    
    
// 复制一个区间进行构造, 可能会导致多分配内存    
    
//              vector(const_iterator first, const_iterator last)    
//                                   ↓    
//                        distance(first, last, n);    
//                                   ↓    
//                      allocate_and_copy(n, first, last);    
//                                   ↓    
//       data_allocator::allocate(n)               <stl_alloc.h>    
//       uninitialized_copy(first, last, result);  <stl_uninitialized.h>    
    
    
  vector(const_iterator first, const_iterator last)     
    size_type n = 0;    
    distance(first, last, n);    
    start = allocate_and_copy(n, first, last);    
    finish = start + n;    
    end_of_storage = finish;    
      
#endif /* __STL_MEMBER_TEMPLATES */    
    
  ~vector()    
      
    // 析构对象    
    destroy(start, finish);    
    // 释放内存    
    deallocate();    
      
    
  vector<T, Alloc>& operator=(const vector<T, Alloc>& x);    
    
  
    
  void reserve(size_type n)    
      
    if (capacity() < n)     
      const size_type old_size = size();    
      iterator tmp = allocate_and_copy(n, start, finish);    
      destroy(start, finish);    
      deallocate();    
      start = tmp;    
      finish = tmp + old_size;    
      end_of_storage = start + n;    
        
      
    
  // 提供访问函数    
  reference front()  return *begin();     
  const_reference front() const  return *begin();     
  reference back()  return *(end() - 1);     
  const_reference back() const  return *(end() - 1);     
    
    
// 向容器尾追加一个元素, 可能导致内存重新分配    
    
//                          push_back(const T& x)    
//                                   |    
//                                   |---------------- 容量已满?    
//                                   |    
//               ----------------------------    
//           No  |                          |  Yes    
//               |                          |    
//               ↓                          ↓    
//      construct(finish, x);       insert_aux(end(), x);    
//      ++finish;                           |    
//                                          |------ 内存不足, 重新分配    
//                                          |       大小为原来的2倍    
//      new_finish = data_allocator::allocate(len);       <stl_alloc.h>    
//      uninitialized_copy(start, position, new_start);   <stl_uninitialized.h>    
//      construct(new_finish, x);                         <stl_construct.h>    
//      ++new_finish;    
//      uninitialized_copy(position, finish, new_finish); <stl_uninitialized.h>    
    
    
  void push_back(const T& x)    
      
    // 内存满足条件则直接追加元素, 否则需要重新分配内存空间    
    if (finish != end_of_storage)     
      construct(finish, x);    
      ++finish;    
        
    else    
      insert_aux(end(), x);    
      
    
  // 交换两个vector, 实际上是交换内部的状态指针    
  void swap(vector<T, Alloc>& x)    
      
    __STD::swap(start, x.start);    
    __STD::swap(finish, x.finish);    
    __STD::swap(end_of_storage, x.end_of_storage);    
      
    
   
    
  iterator insert(iterator position, const T& x)    
      
    size_type n = position - begin();    
    if (finish != end_of_storage && position == end())     
      construct(finish, x);    
      ++finish;    
        
    else    
      insert_aux(position, x);    
    return begin() + n;    
      
    
  iterator insert(iterator position)  return insert(position, T());     
    
#ifdef __STL_MEMBER_TEMPLATES    
    
// 在指定位置插入一个区间    
    
//     insert(iterator position, InputIterator first, InputIterator last)    
//                                   ↓    
//       range_insert(position, first, last, iterator_category(first));    
//                                   ↓    
//                      for ( ; first != last; ++first)     
//                              pos = insert(pos, *first);    
//                               ++pos;    
//                          
    
    
  template <class InputIterator>    
  void insert(iterator position, InputIterator first, InputIterator last)    
      
    range_insert(position, first, last, iterator_category(first));    
      
#else /* __STL_MEMBER_TEMPLATES */    
  void insert(iterator position,    
              const_iterator first, const_iterator last);    
#endif /* __STL_MEMBER_TEMPLATES */    
    
  void insert (iterator pos, size_type n, const T& x);    
    
  void insert (iterator pos, int n, const T& x)    
      
    insert(pos, (size_type) n, x);    
      
    
  void insert (iterator pos, long n, const T& x)    
      
    insert(pos, (size_type) n, x);    
      
    
  void pop_back()    
      
    --finish;    
    destroy(finish);    
      
    
  iterator erase(iterator position)    
      
    if (position + 1 != end())    
      copy(position + 1, finish, position);    
    --finish;    
    destroy(finish);    
    return position;    
      
    
  iterator erase(iterator first, iterator last)    
      
    iterator i = copy(last, finish, first);    
    // 析构掉需要析构的元素    
    destroy(i, finish);    
    finish = finish - (last - first);    
    return first;    
      
    
  // 调整size, 但是并不会重新分配内存空间    
  void resize(size_type new_size, const T& x)    
      
    if (new_size < size())    
      erase(begin() + new_size, end());    
    else    
      insert(end(), new_size - size(), x);    
      
  void resize(size_type new_size)  resize(new_size, T());     
    
  void clear()  erase(begin(), end());     
    
protected:    
  // 分配空间, 并且复制对象到分配的空间处    
  iterator allocate_and_fill(size_type n, const T& x)    
      
    iterator result = data_allocator::allocate(n);    
    __STL_TRY     
      uninitialized_fill_n(result, n, x);    
      return result;    
        
    __STL_UNWIND(data_allocator::deallocate(result, n));    
      
    
// 分配空间并且拷贝一个区间的元素到新分配空间处    
#ifdef __STL_MEMBER_TEMPLATES    
  template <class ForwardIterator>    
  iterator allocate_and_copy(size_type n,    
                             ForwardIterator first, ForwardIterator last)    
      
    iterator result = data_allocator::allocate(n);    
    __STL_TRY     
      uninitialized_copy(first, last, result);    
      return result;    
        
    __STL_UNWIND(data_allocator::deallocate(result, n));    
      
#else /* __STL_MEMBER_TEMPLATES */    
  iterator allocate_and_copy(size_type n,    
                             const_iterator first, const_iterator last)    
      
    iterator result = data_allocator::allocate(n);    
    __STL_TRY     
      uninitialized_copy(first, last, result);    
      return result;    
        
    __STL_UNWIND(data_allocator::deallocate(result, n));    
      
#endif /* __STL_MEMBER_TEMPLATES */    
    
    
#ifdef __STL_MEMBER_TEMPLATES    
  // 初始化一个区间, 使用push_back()操作, 可能引发内存多次重新分配    
  // 解决方案见    
  // template <class InputIterator>    
  // vector(InputIterator first, InputIterator last)    
  // 我评注部分    
  template <class InputIterator>    
  void range_initialize(InputIterator first, InputIterator last,    
                        input_iterator_tag)    
      
    for ( ; first != last; ++first)    
      push_back(*first);    
      
    
  // This function is only called by the constructor.  We have to worry    
  //  about resource leaks, but not about maintaining invariants.    
  template <class ForwardIterator>    
  void range_initialize(ForwardIterator first, ForwardIterator last,    
                        forward_iterator_tag)    
      
    size_type n = 0;    
    distance(first, last, n);    
    start = allocate_and_copy(n, first, last);    
    finish = start + n;    
    end_of_storage = finish;    
      
    
  template <class InputIterator>    
  void range_insert(iterator pos,    
                    InputIterator first, InputIterator last,    
                    input_iterator_tag);    
    
  template <class ForwardIterator>    
  void range_insert(iterator pos,    
                    ForwardIterator first, ForwardIterator last,    
                    forward_iterator_tag);    
    
#endif /* __STL_MEMBER_TEMPLATES */    
;    
    
    
// vector实现部分    
    
    
template <class T, class Alloc>    
inline bool operator==(const vector<T, Alloc>& x, const vector<T, Alloc>& y)    
    
  return x.size() == y.size() && equal(x.begin(), x.end(), y.begin());    
    
    
// 字典序比较    
template <class T, class Alloc>    
inline bool operator<(const vector<T, Alloc>& x, const vector<T, Alloc>& y)    
    
  return lexicographical_compare(x.begin(), x.end(), y.begin(), y.end());    
    
    
#ifdef __STL_FUNCTION_TMPL_PARTIAL_ORDER    
    
template <class T, class Alloc>    
inline void swap(vector<T, Alloc>& x, vector<T, Alloc>& y)    
    
  x.swap(y);    
    
    
#endif /* __STL_FUNCTION_TMPL_PARTIAL_ORDER */    
    
    
// 重载赋值运算符    
    
//                  operator=(const vector<T, Alloc>& x)    
//                                   |    
//                                   |---------------- 是否是自赋值?    
//                                   ↓    
//              -----------------------------------------    
//        No    |                                       | Yes    
//              |                                       |    
//              ↓                                       |------- 容量判断    
//        return *this;                                 |    
//                                                      ↓    
//      -----------------------------------------------------------------    
//      |x.size() > capacity()          | size() >= x.size()            | other    
//      |                               |                               |    
//      ↓                               ↓                               |    
//  容量不足, 需要重新分配        容量足够, 只需要析构掉多余的对象             |    
//  allocate_and_copy(         copy(x.begin(), x.end(), begin());       |    
//      x.end() - x.begin(),   destroy(i, finish);                      |    
//      x.begin(), x.end());                                            |    
//  destroy(start, finish);                                             |    
//  deallocate();                                                       ↓    
//                     copy(x.begin(), x.begin() + size(), start);    
//                     uninitialized_copy(x.begin() + size(), x.end(), finish);    
    
    
template <class T, class Alloc>    
vector<T, Alloc>& vector<T, Alloc>::operator=(const vector<T, Alloc>& x)    
    
  if (&x != this)     
    // 如果x.size() > capacity()那么就需要重新分配内存    
    // 首先分配内存, 并将容器内原来的元素拷贝到新分配内存中    
    // 然后析构原容器中元素, 调整内存状态变量    
    if (x.size() > capacity())     
      iterator tmp = allocate_and_copy(x.end() - x.begin(),    
                                       x.begin(), x.end());    
      destroy(start, finish);    
      deallocate();    
      start = tmp;    
      end_of_storage = start + (x.end() - x.begin());    
        
    else if (size() >= x.size())     
      iterator i = copy(x.begin(), x.end(), begin());    
      destroy(i, finish);    
        
    else     
      copy(x.begin(), x.begin() + size(), start);    
      uninitialized_copy(x.begin() + size(), x.end(), finish);    
        
    finish = start + x.size();    
      
  return *this;    
    
    
    
// 提供插入操作    
    
//                 insert_aux(iterator position, const T& x)    
//                                   |    
//                                   |---------------- 容量是否足够?    
//                                   ↓    
//              -----------------------------------------    
//        Yes   |                                       | No    
//              |                                       |    
//              ↓                                       |    
// 从opsition开始, 整体向后移动一个位置                     |    
// construct(finish, *(finish - 1));                    |    
// ++finish;                                            |    
// T x_copy = x;                                        |    
// copy_backward(position, finish - 2, finish - 1);     |    
// *position = x_copy;                                  |    
//                                                      ↓    
//                            data_allocator::allocate(len);    
//                            uninitialized_copy(start, position, new_start);    
//                            construct(new_finish, x);    
//                            ++new_finish;    
//                            uninitialized_copy(position, finish, new_finish);    
//                            destroy(begin(), end());    
//                            deallocate();    
    
    
template <class T, class Alloc>    
void vector<T, Alloc>::insert_aux(iterator position, const T& x)    
    
  if (finish != end_of_storage)        // 还有剩余内存    
    construct(finish, *(finish - 1));    
    ++finish;    
    T x_copy = x;    
    copy_backward(position, finish - 2, finish - 1);    
    *position = x_copy;    
      
  else         // 内存不足, 需要重新分配    
    // 本实作中是按原内存2倍进行重新分配    
    const size_type old_size = size();    
    const size_type len = old_size != 0 ? 2 * old_size : 1;    
    iterator new_start = data_allocator::allocate(len);    
    iterator new_finish = new_start;    
    // 将内存重新配置    
    __STL_TRY     
      new_finish = uninitialized_copy(start, position, new_start);    
      construct(new_finish, x);    
      ++new_finish;    
      new_finish = uninitialized_copy(position, finish, new_finish);    
        
// 分配失败则抛出异常    
#       ifdef  __STL_USE_EXCEPTIONS    
    catch(...)     
      destroy(new_start, new_finish);    
      data_allocator::deallocate(new_start, len);    
      throw;    
        
#       endif /* __STL_USE_EXCEPTIONS */    
    // 析构原容器中的对象    
    destroy(begin(), end());    
    // 释放原容器分配的内存    
    deallocate();    
    // 调整内存指针状态    
    start = new_start;    
    finish = new_finish;    
    end_of_storage = new_start + len;    
      
    
     
template <class T, class Alloc>    
void vector<T, Alloc>::insert(iterator position, size_type n, const T& x)    
    
  // 如果n为0则不进行任何操作    
  if (n != 0)     
    if (size_type(end_of_storage - finish) >= n)       // 剩下的内存够分配    
      T x_copy = x;    
      const size_type elems_after = finish - position;    
      iterator old_finish = finish;    
      if (elems_after > n)     
        uninitialized_copy(finish - n, finish, finish);    
        finish += n;    
        copy_backward(position, old_finish - n, old_finish);    
        fill(position, position + n, x_copy);    
          
      else     
        uninitialized_fill_n(finish, n - elems_after, x_copy);    
        finish += n - elems_after;    
        uninitialized_copy(position, old_finish, finish);    
        finish += elems_after;    
        fill(position, old_finish, x_copy);    
          
        
    else       // 剩下的内存不够分配, 需要重新分配    
      const size_type old_size = size();    
      const size_type len = old_size + max(old_size, n);    
      iterator new_start = data_allocator::allocate(len);    
      iterator new_finish = new_start;    
      __STL_TRY     
        new_finish = uninitialized_copy(start, position, new_start);    
        new_finish = uninitialized_fill_n(new_finish, n, x);    
        new_finish = uninitialized_copy(position, finish, new_finish);    
          
#         ifdef  __STL_USE_EXCEPTIONS    
      catch(...)     
        destroy(new_start, new_finish);    
        data_allocator::deallocate(new_start, len);    
        throw;    
          
#         endif /* __STL_USE_EXCEPTIONS */    
      destroy(start, finish);    
      deallocate();    
      start = new_start;    
      finish = new_finish;    
      end_of_storage = new_start + len;    
        
      
    
    
#ifdef __STL_MEMBER_TEMPLATES    
    
// 在指定位置插入指定区间的对象    
template <class T, class Alloc> template <class InputIterator>    
void vector<T, Alloc>::range_insert(iterator pos,    
                                    InputIterator first, InputIterator last,    
                                    input_iterator_tag)    
    
  for ( ; first != last; ++first)     
    pos = insert(pos, *first);    
    ++pos;    
      
    
    
template <class T, class Alloc> template <class ForwardIterator>    
void vector<T, Alloc>::range_insert(iterator position,    
                                    ForwardIterator first,    
                                    ForwardIterator last,    
                                    forward_iterator_tag)    
    
  if (first != last)     
    size_type n = 0;    
    distance(first, last, n);    
    if (size_type(end_of_storage - finish) >= n)     
      const size_type elems_after = finish - position;    
      iterator old_finish = finish;    
      if (elems_after > n)     
        uninitialized_copy(finish - n, finish, finish);    
        finish += n;    
        copy_backward(position, old_finish - n, old_finish);    
        copy(first, last, position);    
          
      else     
        ForwardIterator mid = first;    
        advance(mid, elems_after);    
        uninitialized_copy(mid, last, finish);    
        finish += n - elems_after;    
        uninitialized_copy(position, old_finish, finish);    
        finish += elems_after;    
        copy(first, mid, position);    
          
        
    else     
      const size_type old_size = size();    
      const size_type len = old_size + max(old_size, n);    
      iterator new_start = data_allocator::allocate(len);    
      iterator new_finish = new_start;    
      __STL_TRY     
        new_finish = uninitialized_copy(start, position, new_start);    
        new_finish = uninitialized_copy(first, last, new_finish);    
        new_finish = uninitialized_copy(position, finish, new_finish);    
          
#         ifdef __STL_USE_EXCEPTIONS    
      catch(...)     
        destroy(new_start, new_finish);    
        data_allocator::deallocate(new_start, len);    
        throw;    
          
#         endif /* __STL_USE_EXCEPTIONS */    
      destroy(start, finish);    
      deallocate();    
      start = new_start;    
      finish = new_finish;    
      end_of_storage = new_start + len;    
        
      
    
    
#else /* __STL_MEMBER_TEMPLATES */    
    
template <class T, class Alloc>    
void vector<T, Alloc>::insert(iterator position,    
                              const_iterator first,    
                              const_iterator last)     
  if (first != last)     
    size_type n = 0;    
    distance(first, last, n);    
    if (size_type(end_of_storage - finish) >= n)     
      const size_type elems_after = finish - position;    
      iterator old_finish = finish;    
      if (elems_after > n)     
        uninitialized_copy(finish - n, finish, finish);    
        finish += n;    
        copy_backward(position, old_finish - n, old_finish);    
        copy(first, last, position);    
          
      else     
        uninitialized_copy(first + elems_after, last, finish);    
        finish += n - elems_after;    
        uninitialized_copy(position, old_finish, finish);    
        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 = data_allocator::allocate(len);    
      iterator new_finish = new_start;    
      __STL_TRY     
        new_finish = uninitialized_copy(start, position, new_start);    
        new_finish = uninitialized_copy(first, last, new_finish);    
        new_finish = uninitialized_copy(position, finish, new_finish);    
          
#         ifdef __STL_USE_EXCEPTIONS    
      catch(...)     
        destroy(new_start, new_finish);    
        data_allocator::deallocate(new_start, len);    
        throw;    
          
#         endif /* __STL_USE_EXCEPTIONS */    
      destroy(start, finish);    
      deallocate();    
      start = new_start;    
      finish = new_finish;    
      end_of_storage = new_start + len;    
        
      
    
    
#endif /* __STL_MEMBER_TEMPLATES */    
    
#if defined(__sgi) && !defined(__GNUC__) && (_MIPS_SIM != _MIPS_SIM_ABI32)    
#pragma reset woff 1174    
#endif    
    
__STL_END_NAMESPACE    
    
#endif /* __SGI_STL_INTERNAL_VECTOR_H */    
    
// Local Variables:    
// mode:C++    
// End:    

vector迭代器

vector维护的是一个连续的线性空间,不论其元素类型为何,普通指针都可以作为vector的迭代器。vector支持随机存取,而普通指针也有这样的能力。所以,vector提供的是random access 迭代器。

vector数据结构

vector是线性连续空间,一个迭代器start指向头,一个迭代器finish指向使用的结束,代表目前被使用的空间范围,并以end_of_storage指向空间的尾端

当我们使用push_back()将新元素插入vector尾端时,这个函数首先会检查是否有备用空间,如果有,就直接在备用空间上构造元素,然后调整迭代器finish,是vector 的size变大。如果没有空间了,就重新配置-移动数据-释放元空间,可以参见push_back的实现。

所以,这里vector的动态空间分配并不是在原空间之后接续新空间,而是以原空间的两倍另外配置一块较大空间,并释放原空间。


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