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template<class T,class Alloc=alloc>
class vector{
   public:
     //vector的嵌套型别定义
     typedef  T             value_type;
     typedef  value_type*   pointer;
     typedef  value_type*   iterator;
     typedef  value_type*   reference;
     typedef  size_t        size_type;
     typedef  ptrdiff_t     difference_type; 
   protected:
     //simple_alloc 是SGI STL的空间配置器
     typedef simple_alloc<value_type,Alloc> data_allocator;
     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);
     }
 
     void fill_initialize(size_type n,const T& value)
     {
         start=allocate_and_fill(n,value);
         finish=start+n;
         end_of_storage=finsih;
     }
 
  public:
     iterator begin(){return start;}
     iterator end(){return finish;}
     size_type size() const {return size_type(end()-begin());}
     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);}
 
     vector():start(0),finish(0),end_of_storage(0){}
     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(){
         destroy(start,finish);
         deallocate();
     }
 
     reference front(){return *begin();}//第一个元素
     reference back() {return *(end()-1);}//最后一个元素
     void push_back(const T& x){//将元素插入至最尾端
         if(finish!=end_of_storage){
             construct(finish,x);
             ++finish;
         }
         else
            insert_aux(end(),x);
     }
 
     void pop_back(){//将最尾端元素取出
         --finish;
         destroy(finish);//全局函数
     }
 
     iterator erase(iterator position){//清除某位置上的元素
         if(position+1 !=end)
         {
            copy(position+1,finish,position);//后续元素往前移动
         }
         --finish;
         destroy(finish);
         return position;
     }
 
     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:
     //配置空间并填满内容
     iterator allocate_and_fill(size_type n,const T& x)
     {
         iterator result=data_allocator::allocate(n);
         uninitialized_fill_n(result,n,x);
         return result;
     }
};