C++ Primer第18章Vector的再实现及bug修正

 1 #include <iostream>
 2 #include <string>
 3 #include <memory>
 4 using namespace std;
 5 
 6 std::ptrdiff_t max(std::ptrdiff_t a, std::ptrdiff_t b)
 7 {
 8     return a > b ? a : b;
 9 }
10 
11 template <class T> class Vector{
12 public:
13     Vector(): elements(0), first_free(0), end(0) {}
14     void push_back(const T&);
15 
16 private:
17     static std::allocator<T> alloc;
18     void reallocate();
19 public:
20     T * elements;
21     T * first_free;
22     T * end;
23 };
24 
25 template<class T> std::allocator<T> Vector<T>::alloc;//如果没有这句，编译器报错，但如果类Vector中去掉static关键字，这句可以删掉
26 
27 template <class T>
28 void Vector<T>::push_back(const T& t)
29 {
30     if(first_free == end)
31         reallocate();
32     alloc.construct(first_free,t);
33     ++first_free;
34 }
35 
36 template <class T>
37 void Vector<T>::reallocate()
38 {
39     std::ptrdiff_t size = first_free - elements;
40     std::ptrdiff_t newcapacity = 2 * max(size, 1);
41 
42     T * newelements = alloc.allocate(newcapacity);
43 
44     uninitialized_copy(elements, first_free, newelements);
45 
46     for(T * p = first_free; p != elements; alloc.destroy(--p));
47 
48     if(elements)
49         alloc.deallocate(elements, end - elements);
50 
51     elements = newelements;
52     first_free = elements + size;
53     end = elements + newcapacity;
54 }
55 
56 int main()
57 {
58     Vector<string> str;
59     string s;
60     for(int i = 0; i < 5; ++i)
61     {
62         cin>>s;
63         str.push_back(s);
64     }
65     for(string * p = str.elements; p != str.first_free; ++p)
66         cout<<*p<<endl;
67     return 0;
68 }