STL源码剖析 容器 stl_vector.h

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vector

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描述：

1.迭代器

vector 维护的是一个连续线性空间，它的迭代器是普通指针，

能满足 RandomAccessIterator 所有必要条件：operator*, operator->,operator++,operator--,operator+,

operator-,operator+=,operator-=,operator[]

2.数据结构

vector所采用的数据结构是线性连续空间。

迭代器 start、finish分别表示配置得来的连续空间中目前已经被使用的范围

迭代器 end_of_storage 指向整块连续空间的尾端

增加新元素时，如果走过当时的容量，则容量会扩充至两倍。

如果两倍容量仍不足，就扩张至足够大的容量。

扩充容量的过程为：重新配置、元素移动、释放原空间

所谓动态增加大小，并不是在原空间之后接续新空间，因为无法保证原空间之后

尚有可供配置的空间。因此，对 vector 的任何操作，一旦引起空间重新配置，

指向原 vector 的所有迭代器就失效了。

图4-2

示例：

vector<int> V;
V.insert(V.begin(), 3);
assert(V.size() == 1 && V.capacity() >= 1 && V[0] == 3);

源码：

#ifndef __SGI_STL_INTERNAL_VECTOR_H
#define __SGI_STL_INTERNAL_VECTOR_H

__STL_BEGIN_NAMESPACE 

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

template <class T, class Alloc = alloc>
class vector {
public:
  typedef T value_type;
  typedef value_type* pointer;
  typedef const value_type* const_pointer;
  typedef value_type* iterator; //vector 的迭代器是个原生的指针
  typedef const value_type* const_iterator;
  typedef value_type& reference;
  typedef const value_type& const_reference;
  typedef size_t size_type;
  typedef ptrdiff_t difference_type;

#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:
  typedef simple_alloc<value_type, Alloc> data_allocator; //连续空间？
  iterator start; //表示目前使用空间的头
  iterator finish; //表示目前使用空间的尾
  iterator end_of_storage; //表示目前可用空间的尾
  void insert_aux(iterator position, const T& x);
  void deallocate() {
    if (start) data_allocator::deallocate(start, end_of_storage - start);
  }
  // 填充并予以初始化
  void fill_initialize(size_type n, const T& value) {
    start = allocate_and_fill(n, value);
    finish = start + n;
    end_of_storage = finish;
  }
public:
  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());
  }
  size_type size() const { return size_type(end() - begin()); }
  size_type max_size() const { return size_type(-1) / sizeof(T); }
  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); }

  vector() : start(0), finish(0), end_of_storage(0) {}
  //构造函数，允许指定 vector 大小 n 和初值 value
  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); }
  explicit vector(size_type n) { fill_initialize(n, T()); }

  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;
  }
#ifdef __STL_MEMBER_TEMPLATES
  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 */
  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() {
    destroy(start, finish);
    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;
    }
  }
  reference front() { return *begin(); }
  const_reference front() const { return *begin(); }
  reference back() { return *(end() - 1); }
  const_reference back() const { return *(end() - 1); }
  //
  void push_back(const T& x) {
    if (finish != end_of_storage) { //检查是否还有备用空间
      construct(finish, x); //有，直接在备用空间上构造元素
      ++finish; //调整迭代器 finish
    }
    else
      insert_aux(end(), x); //没有，扩充空间(重新配置、元素移动、释放原空间)
  }
  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
  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; //将尾端标记往前移一格，表示将放弃尾端元素
    destroy(finish); //析构尾端元素
  }
  //清除 position 指向的元素
  iterator erase(iterator position) {
    if (position + 1 != end())
      copy(position + 1, finish, position);
    --finish;
    destroy(finish);
    return position;
  }
  //清除[first, last)中的所有元素
  iterator erase(iterator first, iterator last) {
    iterator i = copy(last, finish, first); 将 [last, finish) 指示的元素拷贝至 first 迭代器开头的地方
    destroy(i, finish); 析构[i, finish) 里的元素
    finish = finish - (last - first); 调整 finish 指示的位置 last - first 表示清除掉了的元素个数
    return first;
  }
  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()); }
  //调用 erase 清除所有元素
  void clear() { erase(begin(), end()); }

protected:
  //配置而后填充
  iterator allocate_and_fill(size_type n, const T& x) {
    iterator result = data_allocator::allocate(n); //配置 n 个元素空间
    __STL_TRY {
      uninitialized_fill_n(result, n, x); //全局函数。全根据 result 的类型特性(type traits)决定使用算法 fill_n() 或反复调用  construct() 来完成任务
      return result;
    }
    __STL_UNWIND(data_allocator::deallocate(result, n));
  }

#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
  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 */
};

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());
}

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 */

template <class T, class Alloc>
vector<T, Alloc>& vector<T, Alloc>::operator=(const vector<T, Alloc>& x) {
  if (&x != this) {
    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;
}

template <class T, class Alloc>
void vector<T, Alloc>::insert_aux(iterator position, const T& x) {
  if (finish != end_of_storage) { // 不是备用空间不够才会调用 insert_aux 来插入元素吗？ 为什么还会出现 finish != end_of_storage 的情况 ？
								  // --> 除了 push_back 不够空间时会调用 insert_aux，正常的 insert 也是调用 insert_aux 实现的。

	//为什么不直接 copy_backward(position, finish - 1, finish)， 然后 *position = x_copy 呢？
	construct(finish, *(finish - 1));
    ++finish;
    T x_copy = x;
    copy_backward(position, finish - 2, finish - 1);
    *position = x_copy;
  }
  else { //无备用空间 position == finish
    const size_type old_size = size();
    const size_type len = old_size != 0 ? 2 * old_size : 1;
    //如果原大小为0，则配置1个元素大小的空间，否则配置原大小两倍的空间
	iterator new_start = data_allocator::allocate(len); //实际配置
    iterator new_finish = new_start;
    __STL_TRY {
	  //将原空间的全部内容拷贝到新空间 positition
      new_finish = uninitialized_copy(start, position, new_start);
      //为新元素设定初值 x
	  construct(new_finish, x);
      //调整迭代器 finish
	  ++new_finish;
	  //？？我觉得下面这行代码没用。因为无备用空间的情况，position == finish
      new_finish = uninitialized_copy(position, finish, new_finish);
    }

#       ifdef  __STL_USE_EXCEPTIONS
    catch(...) { //异常竟然可以用三个小点 ... ??
	  //回滚
      destroy(new_start, new_finish);
      data_allocator::deallocate(new_start, len);
      throw;
    }
#       endif /* __STL_USE_EXCEPTIONS */

	//析构并释放原空间
    destroy(begin(), end());
    deallocate();
	//调整迭代器，指向新 vector
    start = new_start;
    finish = new_finish;
    end_of_storage = new_start + len;
  }
}

template <class T, class Alloc>
//从 position 开始，插入 n 个元素，元素初值为 x
void vector<T, Alloc>::insert(iterator position, size_type n, const T& x) {
  if (n != 0) { // 当 n != 0 才进行以下所有操作
    if (size_type(end_of_storage - finish) >= n) { //备用空间大于新增元素个数
      T x_copy = x;
      const size_type elems_after = finish - position; //插入点之后的的现有元素个数
      iterator old_finish = finish;
      if (elems_after > n) { //"插入点之后的的现有元素个数"大于"新增元素个数"
        //空间还没初始化时用 uninitialized_copy ， 已经初始化了用 copy_backward
		uninitialized_copy(finish - n, finish, finish);
        finish += n;
        copy_backward(position, old_finish - n, old_finish);
        fill(position, position + n, x_copy); //从插入点开始填入新值
      }
      else { //"插入点之后的的现有元素个数"小于"新增元素个数"
        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 {//备用空间小于新增元素个数
      const size_type old_size = size();
	  // 首先决定新长度：旧长度的两倍或旧长度+新元素个数，这两个中取最大值
      const size_type len = old_size + max(old_size, n);
      iterator new_start = data_allocator::allocate(len);
      iterator new_finish = new_start;
      __STL_TRY {
	    //先用 uninitialized_copy 将旧 vector 的插入点之前的元素复制到新空间
        new_finish = uninitialized_copy(start, position, new_start);
        //再用 uninitialized_fill_n 将新增元素填入新空间
		new_finish = uninitialized_fill_n(new_finish, n, x);
        //最后再用 uninitialized_copy 将旧 vector 的插入点之后的元素复制到新空间
		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 */
      //清除并释放旧的 vector
	  destroy(start, finish);
      deallocate();
	  //调整标记
      start = new_start;
      finish = new_finish;
      end_of_storage = new_start + len;
    }
  }
}

#ifdef __STL_MEMBER_TEMPLATES

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:

STL源码剖析 容器 stl_vector.h,布布扣,bubuko.com