这个双链表，是我模仿stl的list制作的，只实现了一些基本功能，像merge，transfer这些就没有实现，用户可以用基本操作来自己做外部实现。
我没有选用stl的[begin,end)迭代器模式，而是使用传统的[head,tail]。不过，为了配合stl算法，我还是加了两个begin()，end()方法，模拟了一下stl容器。模拟的还算及格，至少我可以做类似for (; begin != end; ++begin)这样的事，也可以让我的容器搭配一些stl算法，这在之后的demo里可以看到。不过，我的iterator很朴素，所以不能用于std::sort。
至于模拟的实现，我的方法是让所有越界的迭代器都指向一个预先设定好的内存地址。然后用户调用end()方法的时候，就返回指向这个内存地址的迭代器。这样，当我的迭代器越界的时候，就和end()指向的内存地址一样了。
代码采用C++11实现，在Win7 Mingw32 Gcc4.7的环境下，demo运行正常。如果发现写的不对的地方，还请回复一下。
以下是类的实现：
1 #pragma once
2
3 #include <cstddef>
4 #include <stdexcept>
5
6 namespace jt {
7
8 template <class value_t>
9 class list {
10 friend class list<value_t>;
11
12 private:
13 struct node {
14 value_t val;
15 node *next, *prev;
16 } *_head = nullptr,
17 *_tail = nullptr;
18
19 size_t _siz;
20
21 enum { endpointer = 1 };
22
23 public:
24 class iterator {
25 friend class iterator;
26 friend class list<value_t>;
27
28 public:
29 iterator(node *nn = nullptr) { _init(nn); }
30 iterator(const iterator &i) { _init(i.n); }
31
32 value_t& operator*() const { return n->val; }
33 value_t* operator->() const { return &(operator*()); }
34 iterator operator++() { _inc(); return *this; }
35 iterator operator++(int) { iterator tmp = *this; _inc(); return tmp; }
36 iterator operator--() { _dec(); return *this; }
37 iterator operator--(int) { iterator tmp = *this; _dec(); return tmp; }
38 bool operator==(iterator& i) const { return i.n == n; }
39 bool operator!=(iterator& i) const { return i.n != n; }
40
41 private:
42 node *n;
43
44 void _init(node *nn) {
45 if (nn) {
46 n = nn;
47 } else {
48 n = (node*)endpointer;
49 }
50 }
51
52 void _inc() { n = (n->next) ? n->next : (node*)endpointer; } // increment
53 void _dec() { n = (n->prev) ? n->prev : (node*)endpointer; } // decrement
54 };
55
56 list() { clear(); }
57 list(const list<value_t> &l) { if (&l != this) _init(l.begin(), l.end()); }
58 ~list() { clear(); }
59
60 bool empty() const { return !_head; }
61
62 void clear() {
63 if (!empty()) {
64 node *tmp;
65 for (node *n = _head; n; n = tmp) {
66 tmp = n->next;
67 delete n;
68 }
69
70 _head = nullptr;
71 _tail = nullptr;
72 _siz = 0;
73 }
74 }
75
76 void insert(const iterator &pos, const value_t &val) {
77 if (pos.n == _head) {
78 push_front(val);
79 } else {
80 node *n = new node;
81 n->val = val;
82 n->next = pos.n;
83 n->prev = pos.n->prev;
84
85 pos.n->prev->next = pos.n->prev = n;
86 ++_siz;
87 }
88 }
89
90 void erase(const iterator &pos) {
91 if (pos.n == _head) {
92 pop_front();
93 } else if (pos.n == _tail) {
94 pop_back();
95 } else {
96 pos.n->prev->next = pos.n->next;
97 pos.n->next->prev = pos.n->prev;
98 delete pos.n;
99 --_siz;
100 }
101 }
102
103 iterator head() const { return iterator(_head); }
104 iterator tail() const { return iterator(_tail); }
105
106 iterator begin() const { return iterator(_head); }
107 iterator end() const { return iterator((node*)endpointer); }
108
109 void push_front(const value_t &val) {
110 node *n = new node;
111 n->val = val;
112 n->next = _head;
113 n->prev = nullptr;
114
115 if (empty()) _tail = n;
116 else _head->prev = n;
117 _head = n;
118
119 ++_siz;
120 }
121
122 void push_back(const value_t &val) {
123 node *n = new node;
124 n->val = val;
125 n->next = nullptr;
126 n->prev = _tail;
127
128 if (empty()) _head = n;
129 else _tail->next = n;
130 _tail = n;
131
132 ++_siz;
133 }
134
135 void pop_front() {
136 if (_siz == 0) {
137 throw std::logic_error("Empty List");
138 } else if (_siz == 1) {
139 clear();
140 } else {
141 node *tmp = _head->next;
142 delete _head;
143 _head = tmp;
144 _head->prev = nullptr;
145 }
146
147 --_siz;
148 }
149
150 void pop_back() {
151 if (_siz == 0) {
152 throw std::logic_error("Empty List");
153 } else if (_siz == 1) {
154 clear();
155 } else {
156 node *tmp = _tail->prev;
157 delete _tail;
158 _tail = tmp;
159 _tail->next = nullptr;
160 }
161
162 --_siz;
163 }
164
165 value_t front() const { return *head(); }
166 value_t back() const { return *tail(); }
167
168 size_t size() const { return _siz; }
169
170 private:
171 template <class iter>
172 void _init(iter head, iter tail) {
173 clear();
174
175 // copy
176 if (head && tail) {
177 for (; head != tail; ++head) {
178 push_back(*head);
179 }
180 push_back(*tail);
181 }
182 }
183 };
184
185 }
我没有做测试，而是直接做了一个demo。
这个demo是一个正整数的统计计算器。可以插入，删除，求和，求平均数，等等。
以下是demo的代码，同样是C++11：
1 #include "list.h"
2 #include <iostream>
3 #include <string>
4 #include <cstring>
5 #include <cstdio>
6 #include <numeric>
7 #include <algorithm>
8 #include <map>
9 #include <functional>
10
11 int main() {
12 jt::list<unsigned> cont;
13 std::string buf;
14 std::string helpmsg =
15 "h for HELP\n"
16 "s for SUM\n"
17 "a for AVERAGE\n"
18 "z for SIZE\n"
19 "i,n,p for INSERT n AT p\n"
20 "e,n for ERASE AT p\n"
21 "p,n for PUSH_BACK n\n"
22 "q for QUIT";
23
24 int n = -1;
25 int p = -1;
26
27 // create func
28 std::map<char, std::function<void()>> func;
29 func[‘h‘] = [&]() { std::cout << helpmsg << std::endl; };
30 func[‘s‘] = [&]() { std::cout << "sum: " << std::accumulate(cont.begin(), cont.end(), 0) << std::endl; };
31 func[‘a‘] = [&]() { std::cout << "average: " << double(std::accumulate(cont.begin(), cont.end(), 0)) / cont.size() << std::endl; };
32 func[‘z‘] = [&]() { std::cout << "size: " << cont.size() << std::endl; };
33 func[‘i‘] = [&]() {
34 auto i = cont.begin();
35 while (--p) ++i;
36 cont.insert(i, n);
37 };
38 func[‘e‘] = [&]() {
39 auto i = cont.begin();
40 while (--n) { ++i; }
41 cont.erase(i);
42 };
43 func[‘p‘] = [&]() { cont.push_back(n); };
44 func[‘q‘] = [](){};
45
46 char *optargs = "hsaziepq";
47
48 while (buf != "q") {
49 // display
50 std::cout << "\n[ ";
51 std::for_each(cont.head(), cont.end(), [&](const unsigned &n) { std::cout << n << " "; });
52 std::cout << "]" << std::endl;
53
54 // read in args
55 std::cout << optargs << "> ";
56 std::cin >> buf;
57
58 if (!strchr(optargs, buf[0])) {
59 std::cout << "Wrong Argument" << std::endl;
60 } else {
61 sscanf(buf.c_str(), "%*c,%d,%d", &n, &p);
62 func[buf[0]]();
63 }
64 }
65
66 return 0;
67 }
下面我使用demo的记录，看了可能会比较好理解代码一点：
[ ] hsaziepq> h h for HELP s for SUM a for AVERAGE z for SIZE i,n,p for INSERT n AT p e,n for ERASE AT p p,n for PUSH_BACK n q for QUIT [ ] hsaziepq> s sum: 0 [ ] hsaziepq> z size: 0 [ ] hsaziepq> p,1 [ 1 ] hsaziepq> p,5 [ 1 5 ] hsaziepq> p,9 [ 1 5 9 ] hsaziepq> a average: 5 [ 1 5 9 ] hsaziepq> s sum: 15 [ 1 5 9 ] hsaziepq> z size: 3 [ 1 5 9 ] hsaziepq> i,2,3 [ 1 5 2 9 ] hsaziepq> e,3 [ 1 5 9 ] hsaziepq> i,3,2 [ 1 3 5 9 ] hsaziepq> i,2,2 [ 1 2 3 5 9 ] hsaziepq> i,4,4 [ 1 2 3 4 5 9 ] hsaziepq> e,6 [ 1 2 3 4 5 ] hsaziepq> s sum: 15 [ 1 2 3 4 5 ] hsaziepq> a average: 3 [ 1 2 3 4 5 ] hsaziepq> z size: 5 [ 1 2 3 4 5 ] hsaziepq> q
时间： 2024-10-11 10:23:53