简易vector的实现

在这里我们实现了一个简易的vector，没有利用到 stl中的内存分配器，内存分配利用的是new进行分配。其余功能大致实现。

 1 #ifndef _NVECTOR_
 2 #define _NVECTOR_
 3 #include<cstddef>
 4 #include <algorithm>
 5 template<typename T>
 6 class nvector{
 7 public:
 8     typedef T value_type;
 9     typedef value_type* pointer;
10     typedef value_type& reference;
11     typedef value_type* iterator;
12     typedef size_t size_type;
13     typedef ptrdiff_t difference_type;
14 private:
15     iterator start; //迭代器的起始位置
16     iterator finish;
17     iterator end_of_storage;
18     void insert_aux(iterator position, const T& value);
19 public:
20     iterator begin(){return start;}
21     iterator end(){return finish;}
22     size_type size(){return size_type(end()-begin());}
23     size_type capacity(){return size_type(end_of_storage-begin());}
24     bool empty(){return start==finish;}
25     reference operator [](size_type index){return *(begin()+index);}
26     nvector():start(0),finish(0),end_of_storage(0){}
27     nvector(size_type n, const T& value){
28         start = new T[n];
29         for(int i=0;i<n;i++)
30             start[i] = value;
31         finish = start+n;
32         end_of_storage = start+n;
33     }
34     explicit nvector(size_type n){start = new T[n];finish = start; end_of_storage = start+n;}
35     ~nvector(){if(start!=NULL) delete[] start;finish=0;end_of_storage = 0;}
36     reference front(){return *begin();}
37     reference back(){return *(end()-1);}
38     void push_back(const T& value){
39         if(finish!=end_of_storage){
40             *finish = value;
41             ++finish;
42         }else
43             insert_aux(finish, value);
44     }
45     void pop_back(){
46         if(!empty())
47             --finish;
48     }
49     void clear(){
50         finish = start;
51     }
52 };
53
54 template<typename T>
55 void nvector<T>::insert_aux(iterator position,const T& value){
56     if(finish!=end_of_storage){
57         T x_copy = value;
58         copy_backward(position,finish,finish+1);
59         *position = x_copy;
60     }else{
61         const size_type old_size = size();
62         const size_type new_size = old_size!=0?2*old_size:1;
63         iterator new_start = new T[new_size];
64         iterator new_finish = copy(start,position,new_start);
65         T x_copy = value;
66         *new_finish = x_copy;
67         ++new_finish;
68         new_finish = copy(position,finish,new_finish);
69         if(start!=NULL)
70             delete[] start;
71         start = new_start;
72         finish = new_finish;
73         end_of_storage = start+new_size;
74     }
75 }
76
77 #endif