头结点不位于链表里面，只是用于定位，和内核链表不同。
将LinuxList.h添加到我们的工程中。
再添加一个DualCircleList.h文件：
1 #ifndef DUALCIRCLELIST_H
2 #define DUALCIRCLELIST_H
3
4 #include "LinuxList.h"
5 #include "DualLinkList.h"
6
7 namespace DTLib
8 {
9
10 template < typename T >
11 class DualCircleList : public DualLinkList<T>
12 {
13 protected:
14 struct Node : public Object
15 {
16 list_head head;
17 T value;
18 };
19
20 list_head m_header;
21 list_head* m_current;
22
23 list_head* position(int i) const
24 {
25 list_head* ret = const_cast<list_head*>(&m_header); //这里需要进行const_cast转换，否则无法在const函数里面取m_header的地址
26
27 for(int p=0; p<i; p++)
28 {
29 ret = ret->next;
30 }
31
32 return ret;
33 }
34
35 int mod(int i) const
36 {
37 return (this->m_length == 0) ? 0 : (i % this->m_length);;
38 }
39
40 public:
41 DualCircleList()
42 {
43 this->m_length = 0;
44 this->m_step = 1;
45
46 m_current = NULL;
47
48 INIT_LIST_HEAD(&m_header);
49 }
50
51 bool insert(const T& e)
52 {
53 return insert(this->m_length, e);
54 }
55
56 bool insert(int i, const T& e)
57 {
58 bool ret = true;
59 Node* node = new Node();
60
61 i = i % (this->m_length + 1);
62
63 if(node != NULL)
64 {
65 node->value = e;
66
67 list_add_tail(&node->head, position(i)->next);
68
69 this->m_length++;
70 }
71 else
72 {
73 THROW_EXCEPTION(NoEnoughMemoryException, "No memory to create Node object ...");
74 }
75
76 return ret;
77 }
78
79 bool remove(int i)
80 {
81 bool ret = true;
82
83 i = mod(i);
84
85 ret = ((0 <= i) &&(i<this->m_length));
86
87 if( ret )
88 {
89 list_head* toDel = position(i)->next;
90
91 if( m_current == toDel )
92 {
93 m_current = toDel->next;
94 }
95
96 list_del(toDel);
97
98 this->m_length--;
99
100 delete list_entry(toDel, Node, head);
101 }
102
103 return ret;
104 }
105
106 bool set(int i, const T& e) // O(n)
107 {
108 bool ret = true;
109 i = mod(i);
110 ret = ((0 <= i) && (i < this->m_length));
111
112 if( ret )
113 {
114 list_entry(position(i)->next, Node, head)->value = e;
115 }
116
117 return ret;
118 }
119
120 virtual T get(int i) const // O(n)
121 {
122 T ret;
123
124 if( get(i, ret) )
125 {
126 return ret;
127 }
128 else
129 {
130 THROW_EXCEPTION(IndexOutOfBoundsException, "Invalid parameter i to get element ...");
131 }
132
133 return ret;
134 }
135
136 bool get(int i, T& e) const // O(n)
137 {
138 bool ret = true;
139
140 i = mod(i);
141
142 ret = ((0 <= i) && (i < this->m_length));
143
144 if( ret )
145 {
146 e = list_entry(position(i)->next, Node, head)->value;
147 }
148
149 return ret;
150 }
151
152 int find(const T& e) const
153 {
154 int ret = -1;
155
156 int i = 0;
157
158 list_head* slider = NULL;
159
160 list_for_each(slider, &m_header)
161 {
162 if( list_entry(slider, Node, head )->value == e)
163 {
164 ret = i;
165 break;
166 }
167
168 i++;
169 }
170
171 return ret;
172 }
173
174 int length() const
175 {
176 return this->m_length;
177 }
178
179 void clear()
180 {
181 while( this->m_length > 0 )
182 {
183 remove(0);
184 }
185 }
186
187 bool move(int i, int step = 1)
188 {
189 bool ret = (step > 0);
190
191 i = mod(i);
192
193 ret = ret && ((0 <= i) && (i < this->m_length));
194
195 if( ret )
196 {
197 m_current = position(i)->next;
198
199 this->m_step = step;
200 }
201
202 return ret;
203 }
204
205 bool end()
206 {
207 return (m_current == NULL) || (this->m_length == 0);
208 }
209
210 T current()
211 {
212 if( !end() )
213 {
214 return list_entry(m_current, Node, head)->value;
215 }
216 else
217 {
218 THROW_EXCEPTION(InvalidOperationException, "No value at current position ...");
219 }
220 }
221
222 bool next()
223 {
224 int i = 0;
225
226 while((i < this->m_step) && !end())
227 {
228 if( m_current != &m_header )
229 {
230 m_current = m_current->next;
231 i++;
232 }
233 else
234 {
235 m_current = m_current->next;
236 }
237 }
238
239 if( m_current == &m_header )
240 {
241 m_current = m_current->next;
242 }
243
244 return (i == this->m_step);
245 }
246
247 bool pre()
248 {
249 int i = 0;
250
251 while((i < this->m_step) && !end())
252 {
253 if( m_current != &m_header )
254 {
255 m_current = m_current->prev;
256 i++;
257 }
258 else
259 {
260 m_current = m_current->prev;
261 }
262 }
263
264 if( m_current == &m_header )
265 {
266 m_current = m_current->prev;
267 }
268
269 return (i == this->m_step);
270 }
271
272 ~DualCircleList()
273 {
274 clear();
275 }
276 };
277
278 }
279
280 #endif // DUALCIRCLELIST_H
我们的实现中，头结点只为了做定位用，不属于链表中的一个元素，因此，next和pre函数要跳过头结点。
测试程序如下：
1 #include <iostream>
2 #include "DualCircleList.h"
3
4 using namespace std;
5 using namespace DTLib;
6
7
8 int main()
9 {
10 DualCircleList<int> dl;
11
12 for(int i = 0; i < 5; i++)
13 {
14 dl.insert(0, i);
15 dl.insert(0, 5);
16 }
17
18 cout << "begin" << endl;
19
20 dl.move(dl.length() - 1);
21
22 while(dl.find(5) != -1) //所有的5全部被删除后停止循环
23 {
24 if( dl.current() == 5 )
25 {
26 cout << dl.current() << endl;
27
28 dl.remove(dl.find(dl.current()));
29 }
30 else
31 {
32 dl.pre();
33 }
34 }
35
36 cout << "end" << endl;
37
38 for(int i = 0; i < dl.length(); i++)
39 {
40 cout << dl.get(i) << endl;
41 }
42
43 return 0;
44 }
运行结果如下：
使用以下程序访问会得到死循环：
因为当前是一个双向循环链表。
小结：
思考题：
原文地址：https://www.cnblogs.com/wanmeishenghuo/p/9656853.html
时间： 2024-08-15 14:30:47