从 C++ STD::VECTOR的RESIZE和RESERVE看VECTOR的源码实现

  
  class vector : protected _Vector_base<_Tp, _Alloc> 

   explicit vector(size_type __n)
    : _Base(__n, allocator_type())
    { 
        _M_finish = uninitialized_fill_n(_M_start, __n, _Tp()); 
     }
 
  
template <class _Tp, class _Alloc> 
class _Vector_base {
public:
  ~_Vector_base() { _M_deallocate(_M_start, _M_end_of_storage - _M_start); }

    _Vector_base(const _Alloc&)
    : _M_start(0), _M_finish(0), _M_end_of_storage(0) {}
  _Vector_base(size_t __n, const _Alloc&)
    : _M_start(0), _M_finish(0), _M_end_of_storage(0) 
  {
    _M_start = _M_allocate(__n); //申请n字节大小，返回开始地址
    _M_finish = _M_start;//构造时候 没有填充任何元素。vector<int>()
    _M_end_of_storage = _M_start + __n; //+n 说明是连续空间
  }
  
protected:
  _Tp* _M_start; //表示目前使用空间的 头
  _Tp* _M_finish; //表示目前使用空间的 尾
  _Tp* _M_end_of_storage; //表示目前使用空间 可用空间。
  

  typedef simple_alloc<_Tp, _Alloc> _M_data_allocator; //内存分配器
  //申请n字节空间 malloc
  _Tp* _M_allocate(size_t __n)
    { return _M_data_allocator::allocate(__n); }
  //释放：具体怎么实现的不清楚 
  void _M_deallocate(_Tp* __p, size_t __n) 
    { _M_data_allocator::deallocate(__p, __n); }
};

 _Tp* _M_allocate(size_t __n)
    { return _M_data_allocator::allocate(__n); }
    
  //Return size of allocated storage capacity
  //分配的空间大小。在构造时候已经预先分配
  size_type capacity() const
    { return size_type(_M_end_of_storage - begin()); }
    

  void push_back(const _Tp& __x) {//在最尾端插入元素
    if (_M_finish != _M_end_of_storage) {//若有可用的内存空间
      construct(_M_finish, __x);//构造对象
      ++_M_finish;
    }
    else//若没有可用的内存空间,调用以下函数，把x插入到指定位置
      _M_insert_aux(end(), __x);
  }
  
inline void construct(_T1* __p, const _T2& __value) {
  _Construct(__p, __value);
}


  
template <class _T1, class _T2>
//构造函数执行：new（）
//http://www.cplusplus.com/reference/new/operator%20new/
//new (p2) MyClass;
inline void _Construct(_T1* __p, const _T2& __value) {
  new ((void*) __p) _T1(__value);
}
//调用构造函数 new (p)MyClass():
template <class _T1>
inline void _Construct(_T1* __p) {
  new ((void*) __p) _T1();
}
//调用释放函数
template <class _Tp>
inline void _Destroy(_Tp* __pointer) {
  __pointer->~_Tp();
}
  
  
  

  
  

  
void construct(pointer __p, const _Tp &__val) { new (__p) _Tp(__val); }

inline wchar_t* 
uninitialized_copy(const wchar_t* __first, const wchar_t* __last,
                   wchar_t* __result)
{
  memmove(__result, __first, sizeof(wchar_t) * (__last - __first));
  return __result + (__last - __first);
}
  

  template <class _Tp, class _Alloc>
void 
vector<_Tp, _Alloc>::_M_insert_aux(iterator __position)
{
  if (_M_finish != _M_end_of_storage) {
    construct(_M_finish, *(_M_finish - 1));
    ++_M_finish;
    copy_backward(__position, _M_finish - 2, _M_finish - 1);
    *__position = _Tp();
  }
  else {
    const size_type __old_size = size();
    const size_type __len = __old_size != 0 ? 2 * __old_size : 1; //step1 len=2n
    //new 
    iterator __new_start = _M_allocate(__len); //step2 alloc  len
    iterator __new_finish = __new_start;
    __STL_TRY {
      __new_finish = uninitialized_copy(_M_start, __position, __new_start);
      
      construct(__new_finish);
      ++__new_finish;
      __new_finish = uninitialized_copy(__position, _M_finish, __new_finish);
    }
    //02 free 
    __STL_UNWIND((destroy(__new_start,__new_finish), 
                  _M_deallocate(__new_start,__len)));
    destroy(begin(), end()); // ~T()
    _M_deallocate(_M_start, _M_end_of_storage - _M_start); // 回收地址
    
    //reset
    _M_start = __new_start;
    _M_finish = __new_finish;
    _M_end_of_storage = __new_start + __len;
  }
}

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
 
void* memmove(void* dest, void* source, size_t count) {
 
 char* ret = （char*）dest;
 const char* src =(char*) source;
 if (dest <= source || dest >= (source + count)) {
  //正向拷贝
  //copy from lower addresses to higher addresses
  while (count--)
   *(ret++) = *(src++);
 } else {
  //反向拷贝
  //copy from higher addresses to lower addresses
  while (count--)
   *(ret + count) = *(src + count);
 }
 return ret;
}

  uninitialized_copy(const wchar_t* __first, const wchar_t* __last,
                   wchar_t* __result)
{
  memmove(__result, __first, sizeof(wchar_t) * (__last - __first));
  return __result + (__last - __first); //直接跳转 
}
  
   construct(__new_finish, __x); //调用构造函数 new（__new_finish）x()
  
  
  void construct(pointer __p, const _Tp &__val) { new (__p) _Tp(__val); }
  
  
  void destroy(pointer __p) { __p->~_Tp(); }