练习13.39
1 #include <iostream>
2 #include <string>
3 #include <utility>
4 #include <memory>
5
6 using namespace std;
7
8 class StrVec {
9 public:
10 StrVec() : elements(nullptr), first_free(nullptr), cap(nullptr) {}
11 StrVec(const StrVec&);
12 StrVec& operator=(const StrVec&);
13 ~StrVec();
14 void push_back(const string &);
15 size_t size() const { return first_free - elements; }
16 size_t capacity() const { return cap - elements; }
17 string *begin() const { return elements; }
18 string *end() const { return first_free; }
19 private:
20 string *elements;
21 string *first_free;
22 string *cap;
23 pair<string *, string *> alloc_n_copy(const string *, const string *);
24 void chk_n_alloc() { if (size() == capacity()) reallocate(); }
25 static allocator<string> alloc;
26 void free();
27 void reallocate();
28 };
29
30 int main()
31 {
32 system("pause");
33 return 0;
34 }
35
36 StrVec::StrVec(const StrVec &s)
37 {
38 auto newdata = alloc_n_copy(s.begin(), s.end());
39 elements = newdata.first;
40 first_free = cap = newdata.second;
41 }
42
43 StrVec & StrVec::operator=(const StrVec &rhs)
44 {
45 auto data = alloc_n_copy(rhs.begin(), rhs.end());
46 free();
47 elements = data.first;
48 first_free = cap = data.second;
49 return *this;
50 }
51
52 StrVec::~StrVec()
53 {
54 free();
55 }
56
57 void StrVec::push_back(const string &s)
58 {
59 chk_n_alloc();
60 alloc.construct(first_free++, s);
61 }
62
63 pair<string*, string*> StrVec::alloc_n_copy(const string *b, const string *e)
64 {
65 auto data = alloc.allocate(e - b);
66 return{ data,uninitialized_copy(b,e,data) };
67 }
68
69 void StrVec::free()
70 {
71 if (elements)
72 {
73 for (auto p = first_free; p != elements;)
74 alloc.destroy(--p);
75 alloc.deallocate(elements, cap - elements);
76 }
77 }
78
79 void StrVec::reallocate()
80 {
81 auto newcapacity = size() ? 2 * size() : 1;
82 auto newdata = alloc.allocate(newcapacity);
83 auto dest = newdata;
84 auto elem = elements;
85 for (size_t i = 0; i != size(); ++i)
86 alloc.construct(++dest, std::move(*elem++));
87 free();
88 elements = newdata;
89 first_free = dest;
90 cap = elements + newcapacity;
91 }
练习13.40
1 #include <iostream>
2 #include <string>
3 #include <utility>
4 #include <memory>
5
6 using namespace std;
7
8 class StrVec {
9 public:
10 StrVec() : elements(nullptr), first_free(nullptr), cap(nullptr) {}
11 StrVec(const initializer_list<string> &s);
12 StrVec(const StrVec&);
13 StrVec& operator=(const StrVec&);
14 ~StrVec();
15 void push_back(const string &);
16 size_t size() const { return first_free - elements; }
17 size_t capacity() const { return cap - elements; }
18 string *begin() const { return elements; }
19 string *end() const { return first_free; }
20 void resize(size_t n, const string&);
21 void Reserve(const size_t& len);//重新分配大小
22 private:
23 string *elements;
24 string *first_free;
25 string *cap;
26 pair<string *, string *> alloc_n_copy(const string *, const string *);
27 void chk_n_alloc() { if (size() == capacity()) reallocate(); }
28 static allocator<string> alloc;
29 void free();
30 void reallocate();
31 };
32
33 int main()
34 {
35 system("pause");
36 return 0;
37 }
38
39 StrVec::StrVec(const initializer_list<string>& s)
40 {
41 auto newzone = alloc_n_copy(s.begin(), s.end());
42 elements = newzone.first;
43 first_free = cap = newzone.second;
44 }
45
46 /*StrVec(const initializer_list<string> &vs)
47 {
48 elements = nullptr;
49 first_free = nullptr;
50 cap = nullptr;
51 for (auto it : vs)
52 this->Push_back(it);
53 }*/ //这两种都行应该
54
55 StrVec::StrVec(const StrVec &s)
56 {
57 auto newdata = alloc_n_copy(s.begin(), s.end());
58 elements = newdata.first;
59 first_free = cap = newdata.second;
60 }
61
62 StrVec & StrVec::operator=(const StrVec &rhs)
63 {
64 auto data = alloc_n_copy(rhs.begin(), rhs.end());
65 free();
66 elements = data.first;
67 first_free = cap = data.second;
68 return *this;
69 }
70
71 StrVec::~StrVec()
72 {
73 free();
74 }
75
76 void StrVec::push_back(const string &s)
77 {
78 chk_n_alloc();
79 alloc.construct(first_free++, s);
80 }
81
82 void StrVec::resize(size_t n, const string &s)
83 {
84 if (n == size())
85 return;
86 else if (n > size())
87 {
88 if (n > capacity())
89 {
90 Reserve(n);
91 for (auto i = 0; i != n - size();)
92 alloc.construct(first_free++, s);
93 }
94 else
95 {
96 for (auto i = 0; i != n - size();)
97 alloc.construct(first_free++, s);
98 }
99 }
100 else
101 {
102 auto flag = first_free;
103 while (first_free - elements != n)
104 alloc.destroy(--first_free);
105 alloc.deallocate(flag, size() - n);
106 }
107 }
108
109 pair<string*, string*> StrVec::alloc_n_copy(const string *b, const string *e)
110 {
111 auto data = alloc.allocate(e - b);
112 return{ data,uninitialized_copy(b,e,data) };
113 }
114
115 void StrVec::free()
116 {
117 if (elements)
118 {
119 for (auto p = first_free; p != elements;)
120 alloc.destroy(--p);
121 alloc.deallocate(elements, cap - elements);
122 }
123 }
124
125 void StrVec::reallocate()
126 {
127 auto newcapacity = size() ? 2 * size() : 1;
128 auto newdata = alloc.allocate(newcapacity);
129 auto dest = newdata;
130 auto elem = elements;
131 for (size_t i = 0; i != size(); ++i)
132 alloc.construct(++dest, std::move(*elem++));
133 free();
134 elements = newdata;
135 first_free = dest;
136 cap = elements + newcapacity;
137 }
138
139 void StrVec::Reserve(const size_t& len)//重新分配大小
140 {
141 if (len <= cap - elements)//小于或等于不申请
142 return;
143 //未构造的内存减少
144 auto newcapacity = len;
145 auto newdata = alloc.allocate(newcapacity);//申请len倍内存
146 auto dest = newdata;//alloc返回的首指针
147 auto elem = elements;
148 for (size_t i = 0;i != size();++i)
149 alloc.construct(dest++, move(*elem++));
150 free();
151 elements = newdata;//新的首指针
152 first_free = dest;
153 cap = elements + newcapacity;
154 }
练习13.41
因为first_free所指的位置是最后一个存放元素后一个位置，所以应该用后置递增运算，这样就能依次的进行添加，如果用前置，中间会空出一个内存，这种情况是未定义的；
练习13.42
将原先的代码的vector模板改为StrVec类就可以了
练习13.43
1 void StrVec::free()
2 {
3 if (elements)
4 {
5 for_each(elements, first_free, [this](string &p) { alloc.destroy(&p);});
6 /*for (auto p = first_free; p != elements;)
7 alloc.destroy(--p);*/
8 alloc.deallocate(elements, cap - elements);
9 }
10 }
练习13.44
1 #include <iostream>
2 #include <string>
3 #include <utility>
4 #include <memory>
5 #include <algorithm>
6
7 using namespace std;
8
9 class String {
10 friend ostream &print(ostream &os, String &s);
11 public:
12 String(): element(nullptr), first_free(nullptr) {}
13 String(char *);
14 private:
15 static allocator<char> alloc;
16 char *element;
17 char *first_free;
18 };
19 allocator<char> String::alloc;
20 ostream &print(ostream &os, String &s);
21
22 int main()
23 {
24 String s1;
25 String s2("hello");
26 String s3("hello world");
27 print(cout, s1);
28 print(cout, s2);
29 print(cout, s3);
30 system("pause");
31 return 0;
32 }
33
34 String::String(char *s)
35 {
36 int i = 0;
37 while (s[i] != ‘\0‘)
38 ++i;
39 auto newloc = alloc.allocate(i);
40 auto dest = newloc;
41 for (auto count = 0; count != i;++count)
42 alloc.construct(dest++, s[count]);
43 element = newloc;
44 first_free = dest;
45 }
46
47 ostream & print(ostream &os,String &s)
48 {
49 while (s.element != s.first_free)
50 {
51 os << *(s.element);
52 s.element++;
53 }
54 cout << endl;
55 return os;
56 // TODO: 在此处插入 return 语句
57 }
时间： 2024-08-27 09:42:37