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本篇内容介绍了“如何用Linux内核链表来实现DTLib中的双向循环链表”的有关知识，在实际案例的操作过程中，不少人都会遇到这样的困境，接下来就让小编带领大家学习一下如何处理这些情况吧！希望大家仔细阅读，能够学有所成！
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继承关系如下图所示
下来我们来讲讲它的设计思路：数据结点之间在逻辑上构成双向循环链表，头结点仅用于结点的定位。如下图所示
实现思路：
1、通过模板定义 DualCircleList 类。继承自 DualLinkList 类；
2、在 DualCircleList 内部使用 Linux 内核链表进行实现；
3、使用 struct list_head 定义 DualCircleList 的头结点；
4、特殊处理：循环遍历时忽略头结点
实现要点：
1、通过 list_head 进行目标结点定位（position(i)）；
2、通过 list_entry 将 list_head 指针转换为目标结点指针；
3、通过 list_for_each 实现 int find(const T& e) 函数；
4、遍历函数中的 next() 和 pre() 需要考虑跳过头结点
下来我们来看看基于 Linux 内核链表的双向循环链表是怎样写的
DualCircleList 源码
#ifndef DUALCIRCLELIST_H
#define DUALCIRCLELIST_H
#include "DualLinkList.h"
#include "LinuxList.h"
namespace DTLib
{
template < typename T >
class DualCircleList : public DualLinkList
{
protected:
struct Node : public Object
{
list_head head;
T value;
};
list_head m_header;
list_head* m_current;
list_head* position(int i) const
{
list_head* ret = const_cast(&m_header);
for(int p=0; pnext;
}
return ret;
}
int mod(int i) const
{
return (this->m_length == 0) ? 0 : (i % this->m_length);
}
public:
DualCircleList()
{
this->m_length = 0;
this->m_step = 1;
m_current = NULL;
INIT_LIST_HEAD(&m_header);
}
bool insert(const T& e)
{
return insert(this->m_length, e);
}
bool insert(int i, const T& e)
{
bool ret = true;
Node* node = new Node();
i = i % (this->m_length + 1);
if(node != NULL)
{
node->value = e;
list_add_tail(&node->head, position(i)->next);
this->m_length++;
}
else
{
THROW_EXCEPTION(NoEnoughMemoryException, "No memory to insert new element ...");
}
return ret;
}
bool remove(int i)
{
bool ret = true;
i = mod(i);
ret = ((0 <= i) && (i < this->m_length));
if( ret )
{
list_head* toDel = position(i)->next;
if( m_current == toDel )
{
m_current = toDel->next;
}
list_del(toDel);
this->m_length--;
delete list_entry(toDel, Node, head);
}
return ret;
}
bool set(int i, const T& e)
{
bool ret = true;
i = mod(i);
ret = ((0 <= i) && (i < this->m_length));
if( ret )
{
list_entry(position(i)->next, Node, head)->value = e;
}
return ret;
}
T get(int i) const
{
T ret;
if( get(i, ret) )
{
return ret;
}
else
{
THROW_EXCEPTION(IndexOutOfBoundsException, "Invaild parameter i to get element ...");
}
}
bool get(int i, T& e) const
{
bool ret = true;
i = mod(i);
ret = ((0 <= i) && (i < this->m_length));
if( ret )
{
e = list_entry(position(i)->next, Node, head)->value;
}
return ret;
}
int find(const T& e) const
{
int ret = -1;
int i = 0;
list_head* slider = NULL;
list_for_each(slider, &m_header)
{
if( list_entry(slider, Node, head)->value == e )
{
ret = i;
break;
}
i++;
}
return ret;
}
int length() const
{
return this->m_length;
}
void clear()
{
while( this->m_length > 0 )
{
remove(0);
}
}
bool move(int i, int step = 1)
{
bool ret = (step > 0);
i = mod(i);
ret = ret && ((0 <= i) && (i < this->m_length));
if( ret )
{
m_current = position(i)->next;
this->m_step = step;
}
return ret;
}
bool end()
{
return (m_current == NULL) || (this->m_length == 0);
}
T current()
{
if( !end() )
{
return list_entry(m_current, Node, head)->value;
}
else
{
THROW_EXCEPTION(INvalidOPerationException, "No value at current position ...");
}
}
bool next()
{
int i = 0;
while( (i < this->m_step) && !end() )
{
if( m_current != &m_header )
{
m_current = m_current->next;
i++;
}
else
{
m_current = m_current->next;
}
}
if( m_current == &m_header )
{
m_current = m_current->next;
}
return (i == this->m_step);
}
bool pre()
{
int i =0;
while( (i < this->m_step) && !end() )
{
if( m_current != &m_header )
{
m_current = m_current->next;
i++;
}
else
{
m_current = m_current->prev;
}
}
if( m_current == &m_header )
{
m_current = m_current->next;
}
return (i == this->m_step);
}
~DualCircleList()
{
clear();
}
};
}
#endif // DUALCIRCLELIST_H 下来我们写点测试代码看看上面的代码有没有问题
main.cpp 源码
