动手实现自己的 STL 容器 《1》---- vector

本文参考了侯捷的 《STL 源码分析》一书，出于兴趣，自行实现了简单的 vector 容器。

之后会陆续上传 list， deque 等容器的代码，若有错误，欢迎留言指出。

vector 容易实现的几点注意事项：

1. 由于vector 是动态数组。

出于效率的考虑，在往vector 中加入元素时，内存的扩展遵循的规则是：

1> 如果当前可用内存不够，开 2倍大的内存，将原来的数组复制到新数组中，撤销原来的数组。

2> 加入新的元素

2. 通常当我们 int *p = new int(1)时， new 其实做了两件事情： 1> 分配内存   2>在分配的内存中调用类的构造函数。

出于效率的考虑，在 vector 的内存管理中，我们将这两个操作分开。

C++ 提供了 模板类 allocator 来实现上述的功能。

3. vector 中三个指针，分别是 start, finish, end_of_storage;

[start, finish) 就是数组元素；

[finish, end_of_storage) 是预先分配的空间（还没有调用构造函数）

参考书籍：

1. C++ primer， Lippman

2. STL 源码分析， 侯捷

// Last Update:2014-04-11 15:44:44
/**
 * @file vector.h
 * @brief a simple vector class
 * @author shoulinjun@126.com
 * @version 0.1.00
 * @date 2014-04-09
 */

#ifndef MY_VECTOR_H
#define MY_VECTOR_H

#include <iostream>
#include <algorithm>
#include <memory>

template<class T>
void destroy(T* pointer)
{
  pointer->~T();
}

template<class ForwardIterator>
void destroy(ForwardIterator first, ForwardIterator last)
{
  for(ForwardIterator it = first; it != last; ++ it)
  {
    destroy(&*it);
  }
}

template<class T>
class MyVector
{
public:
  typedef T  value_type;
  typedef T* iterator;
  typedef const T*const_iterator;
  typedef T* pointer;
  typedef const T* const_pointer;
  typedef T& reference;
  typedef const T& const_reference;
  typedef size_t size_type;

  MyVector();
  MyVector(size_type n, T value = T());
  MyVector(iterator begin, iterator end);
  ~MyVector();

  //copy control
  MyVector(const MyVector&);
  MyVector& operator=(const MyVector&);

  bool empty() const { return begin() == end(); }
  size_type size() const {return (size_type)(finish - start);}
  size_type capacity() const {return (size_type)(end_of_storage - start);}

  iterator begin() { return start; }
  const_iterator begin() const{ return start; }
  iterator end()   { return finish;}
  const_iterator end() const{ return finish; }

  reference operator[](size_type i){return *(start + i);}
  const_reference operator[](size_type i)const {return *(start + i);}

  void insert(iterator position, size_type n, const T& value);
  void push_back(const T& value);
  void pop_back();

  void erase(iterator first, iterator last);
  void clear();

  void reserve(size_type n);
protected:
  iterator start;   //空间的头
  iterator finish;  //空间的尾
  iterator end_of_storage; //可用空间的尾巴
private:
  static std::allocator<T> alloc; // object to get raw memory
};

// static class member needed to be defined outside of class
template<class T>
std::allocator<T> MyVector<T>::alloc;

// default constructor
template<class T>
MyVector<T>::MyVector()
  : start(NULL), finish(NULL), end_of_storage(NULL)
{
}

template<class T>
MyVector<T>::MyVector(size_type n, T value)
{
  start = alloc.allocate(n);
  end_of_storage = finish = start + n;

  for(iterator i=start; i!=finish; ++i)
    alloc.construct(i, value);
}

template<class T>
MyVector<T>::MyVector(iterator begin, iterator end)
{
  const size_type n = end - begin;
  /* allocate space */
  start = alloc.allocate(n);
  finish = end_of_storage = start + n;

  /* call constructor */
  std::uninitialized_copy(begin, end, start);
}

template<class T>
MyVector<T>::~MyVector()
{
  /* call destructor */
  ::destroy(start, finish);

  /* free space */
  alloc.deallocate(start, end_of_storage - start);
}

// copy control
template<class T>
MyVector<T>::MyVector(const MyVector& rhs)
{
  start = alloc.allocate(rhs.capacity());
  std::uninitialized_copy(rhs.start, rhs.finish, start);
  finish = start + (rhs.finish - rhs.start);
  end_of_storage = start + (rhs.end_of_storage - rhs.start);
}

template<class T>
MyVector<T>& MyVector<T>::operator=(const MyVector& rhs)
{
  start = alloc.allocate(rhs.capacity());
  std::uninitialized_copy(rhs.start, rhs.finish, start);
  finish = start + rhs.finish - rhs.start;
  end_of_storage = start + rhs.end_of_storage - rhs.start;

  return *this;
}

template<class T>
void MyVector<T>::insert(iterator position, size_type n, const T& value)
{
  if(n <= end_of_storage - finish)
  {/* enough memory */
    if(n <= finish - position)
    {
      std::uninitialized_copy(finish-n, finish, finish);
      std::copy(position, finish-n, position+n);
      std::fill_n(position, n, value);
    }
    else
    {
      std::uninitialized_fill_n(finish, n - (finish - position), value);
      std::uninitialized_copy(position, finish, position + n);
      std::fill(position, finish, value);
    }
    finish += n;
  }
  else
  {/* reallocate */
    pointer new_start(NULL), new_finish(NULL);
    size_type old_type = end_of_storage - start;
    size_type new_size = old_type + std::max(old_type, n);
    new_start = alloc.allocate(new_size);

    // copy old vector to new vector
    new_finish = std::uninitialized_copy(start, position, new_start);
    std::uninitialized_fill_n(new_finish, n, value);
    new_finish += n;
    new_finish = std::uninitialized_copy(position, finish, new_finish);

    alloc.deallocate(start, end_of_storage - start);

    start = new_start;
    finish = new_finish;
    end_of_storage = new_start + new_size;
  }
}

template<class T>
void MyVector<T>::push_back(const T &value)
{
  insert(end(), 1, value);
}

template<class T>
void MyVector<T>::pop_back()
{
  alloc.destroy(--finish);
}

template<class T>
void MyVector<T>::erase(iterator first, iterator last)
{
  iterator old_finish = finish;
  finish = std::copy(last, finish, first);
  ::destroy(finish, old_finish);
}

template<class T>
void MyVector<T>::clear()
{
  erase(start, finish);
}

template<class T>
void MyVector<T>::reserve(size_type n)
{
  if(capacity() < n)
  {
    iterator new_start = alloc.allocate(n);
    std::uninitialized_copy(start, finish, new_start);

    ::destroy(start, finish);
    alloc.deallocate(start, size());

    const size_type old_size = finish - start;
    start = new_start;
    finish = new_start + old_size;
    end_of_storage = new_start + n;
  }
}

#endif  /*MY_VECTOR_H*/