std::allocator即空间配置器，用于内存分配。更多的细节建议大家研究相关源码。
这里仅是利用std::allocator来实现简单的自定义vector类，如有问题欢迎指正。
1 #include <iostream>
2 #include <memory>
3 using std::cout;
4 using std::endl;
5
6 template <typename Tp>
7 class Vector
8 {
9 public:
10 Vector()
11 : _elems(NULL)
12 , _first_free(NULL)
13 , _end(NULL)
14 {}
15
16 ~Vector()
17 {
18 if(_elems)
19 {
20 while(_elems != _first_free)
21 _alloc.destroy(--_first_free);
22 _alloc.deallocate(_elems,capacity());
23 }
24 }
25
26 void push_back(const Tp & value)
27 {
28 if(size() == capacity())
29 {
30 reallocate();
31 }
32 _alloc.construct(_first_free++,value);
33 }
34
35 void pop_back()
36 {
37 if(size() > 0)
38 {
39 _alloc.destory(--_first_free);
40 }
41 }
42
43 size_t size() const
44 {
45 return _first_free - _elems;
46 }
47 size_t capacity() const
48 {
49 return _end - _elems;
50 }
51
52 Tp & operator[](size_t idx)
53 {
54 return _elems[idx];
55 }
56
57 private:
58 void reallocate()
59 {
60 size_t oldCapacity = capacity();
61 size_t newCapacity = oldCapacity == 0 ? 1 : oldCapacity * 2;
62
63 Tp * newElems = _alloc.allocate(newCapacity);
64 if(_elems)
65 {
66 std::uninitialized_copy(_elems,_first_free,newElems);
67 while(_elems != _first_free)
68 _alloc.destroy(--_first_free);
69 _alloc.deallocate(_elems,oldCapacity);
70 }
71 _elems = newElems;
72 _first_free = _elems + oldCapacity;
73 _end = _elems + newCapacity;
74 }
75 private:
76 static std::allocator<Tp> _alloc;
77 Tp * _elems;
78 Tp * _first_free;
79 Tp * _end;
80 };
81
82 template <typename Tp>
83 std::allocator<Tp> Vector<Tp>::_alloc;
84
85 void display(Vector<int> & vec)
86 {
87 cout << "vec‘s size = " << vec.size() << endl;
88 cout << "vec‘s capacity = " << vec.capacity() << endl;
89 }
以下是测试代码：
1 int test（）
2 {
3 Vector<int> vecInt;
4 display(vecInt);
5
6 vecInt.push_back(1);
7 display(vecInt);
8 vecInt.push_back(2);
9 display(vecInt);
10 vecInt.push_back(3);
11 display(vecInt);
12 vecInt.push_back(4);
13 display(vecInt);
14 vecInt.push_back(5);
15 display(vecInt);
16 vecInt.push_back(6);
17 display(vecInt);
18 vecInt.push_back(7);
19 display(vecInt);
20
21 for(size_t idx = 0; idx != vecInt.size(); ++idx)
22 {
23 cout << vecInt[idx] << " ";
24 }
25 cout << endl;
26 return 0;
27 }
测试结果：
1 vec‘s size = 0 2 vec‘s capacity = 0 3 vec‘s size = 1 4 vec‘s capacity = 1 5 vec‘s size = 2 6 vec‘s capacity = 2 7 vec‘s size = 3 8 vec‘s capacity = 4 9 vec‘s size = 4 10 vec‘s capacity = 4 11 vec‘s size = 5 12 vec‘s capacity = 8 13 vec‘s size = 6 14 vec‘s capacity = 8 15 vec‘s size = 7 16 vec‘s capacity = 8 17 1 2 3 4 5 6 7
时间： 2024-12-20 20:02:37