我发布了一个类似的问题，但我再次提问，因为我的尝试错了。所以现在这是一个完全不同的问题。
这是关于Payroll对象链接列表的学校项目的一部分。我教授的反馈表明我需要从内部 InList函数遍历链表。我明白他在说什么，但不知道怎么做。
在InList函数中，我传递一个链表和一个int，创建Payroll对象并将int指定为员工编号变量。然后使用nodeType当前指针遍历列表并打印记录（如果找到）。
void InList(const orderedLinkedList<Payroll>& P, int employee_number)
{
int listCount = P.length();
Payroll object;
object.setEmployeeNumber(employee_number);
nodeType<Payroll> *current; //how to initialize this?
if (P.isEmptyList())
cout << "Sorry, there is nothing in the list yet." << endl;
else
{
while (current != NULL && listCount > 0)
{
if (current->info.getEmployeeNumber() == employee_number)
{
current->info.printPayroll();
}
listCount--;
current = current->link;
} //end while
} //end else
}
以下是链表的所有功能。请注意，此头文件没有任何成员变量，并且派生自具有第一个和最后一个指针的虚拟基类。另请注意，第一个和最后一个在基类中受到保护。
template <class Type>
bool orderedLinkedList<Type>::search(const Type& searchItem) const
{
bool found = false;
nodeType<Type> *current; //pointer to traverse the list
current = first; //start the search at the first node
while (current != NULL && !found)
if (current->info >= searchItem)
found = true;
else
current = current->link;
if (found)
found = (current->info == searchItem); //test for equality
return found;
}//end search
template <class Type>
void orderedLinkedList<Type>::insert(const Type& newItem)
{
nodeType<Type> *current; //pointer to traverse the list
nodeType<Type> *trailCurrent = NULL;//pointer just before current
nodeType<Type> *newNode; //pointer to create a node
bool found;
newNode = new nodeType<Type>; //create the node
newNode->info = newItem; //store newItem in the node
newNode->link = NULL; //set the link field of the node
//to NULL
if (first == NULL) //Case 1
{
first = newNode;
last = newNode;
count++;
}
else
{
current = first;
found = false;
while (current != NULL && !found) //search the list
if (current->info >= newItem)
found = true;
else
{
trailCurrent = current;
current = current->link;
}
if (current == first) //Case 2
{
newNode->link = first;
first = newNode;
count++;
}
else //Case 3
{
trailCurrent->link = newNode;
newNode->link = current;
if (current == NULL)
last = newNode;
count++;
}
}//end else
}//end insert
template<class Type>
void orderedLinkedList<Type>::insertFirst(const Type& newItem)
{
insert(newItem);
}//end insertFirst
template<class Type>
void orderedLinkedList<Type>::insertLast(const Type& newItem)
{
insert(newItem);
}//end insertLast
template<class Type>
void orderedLinkedList<Type>::deleteNode(const Type& deleteItem)
{
nodeType<Type> *current; //pointer to traverse the list
nodeType<Type> *trailCurrent = NULL; //pointer just before current
bool found;
if (first == NULL) //Case 1
cout << "Cannot delete from an empty list." << endl;
else
{
current = first;
found = false;
while (current != NULL && !found) //search the list
if (current->info >= deleteItem)
found = true;
else
{
trailCurrent = current;
current = current->link;
}
if (current == NULL) //Case 4
cout << "The item to be deleted is not in the "
<< "list." << endl;
else
if (current->info == deleteItem) //the item to be
//deleted is in the list
{
if (first == current) //Case 2
{
first = first->link;
if (first == NULL)
last = NULL;
delete current;
}
else //Case 3
{
trailCurrent->link = current->link;
if (current == last)
last = trailCurrent;
delete current;
}
count--;
}
else //Case 4
cout << "The item to be deleted is not in the "
<< "list." << endl;
}
}//end deleteNode
这是虚拟基类：
#pragma once
#ifndef H_LinkedListType
#define H_LinkedListType
#include <iostream>
#include <cassert>
using namespace std;
//Definition of the node
template <class Type>
struct nodeType
{
Type info;
nodeType<Type> *link;
};
template <class Type>
class linkedListIterator
{
public:
linkedListIterator();
linkedListIterator(nodeType<Type> *ptr);
Type operator*();
linkedListIterator<Type> operator++();
bool operator==(const linkedListIterator<Type>& right) const;
bool operator!=(const linkedListIterator<Type>& right) const;
private:
nodeType<Type> *current; //pointer to point to the current
};
template <class Type>
linkedListIterator<Type>::linkedListIterator()
{
current = NULL;
}
template <class Type>
linkedListIterator<Type>::
linkedListIterator(nodeType<Type> *ptr)
{
current = ptr;
}
template <class Type>
Type linkedListIterator<Type>::operator*()
{
return current->info;
}
template <class Type>
linkedListIterator<Type> linkedListIterator<Type>::operator++()
{
current = current->link;
return *this;
}
template <class Type>
bool linkedListIterator<Type>::operator==
(const linkedListIterator<Type>& right) const
{
return (current == right.current);
}
template <class Type>
bool linkedListIterator<Type>::operator!=
(const linkedListIterator<Type>& right) const
{
return (current != right.current);
}
//***************** class linkedListType ****************
template <class Type>
class linkedListType
{
public:
const linkedListType<Type>& operator=
(const linkedListType<Type>&);
void initializeList();
bool isEmptyList() const;
void print() const;
int length() const;
void destroyList();
Type front() const;
Type back() const;
virtual bool search(const Type& searchItem) const = 0;
virtual void insertFirst(const Type& newItem) = 0;
virtual void insertLast(const Type& newItem) = 0;
virtual void deleteNode(const Type& deleteItem) = 0;
linkedListIterator<Type> begin();
linkedListIterator<Type> end();
linkedListType();
linkedListType(const linkedListType<Type>& otherList);
~linkedListType();
protected:
int count; //variable to store the number of elements in the list
nodeType<Type> *first; //pointer to the first node of the list
nodeType<Type> *last; //pointer to the last node of the list
private:
void copyList(const linkedListType<Type>& otherList);
};
template <class Type>
bool linkedListType<Type>::isEmptyList() const
{
return(first == NULL);
}
template <class Type>
linkedListType<Type>::linkedListType() //default constructor
{
first = NULL;
last = NULL;
count = 0;
}
template <class Type>
void linkedListType<Type>::destroyList()
{
nodeType<Type> *temp; //pointer to deallocate the memory
//occupied by the node
while (first != NULL) //while there are nodes in the list
{
temp = first; //set temp to the current node
first = first->link; //advance first to the next node
delete temp; //deallocate the memory occupied by temp
}
last = NULL; //initialize last to NULL; first has already
//been set to NULL by the while loop
count = 0;
}
template <class Type>
void linkedListType<Type>::initializeList()
{
destroyList(); //if the list has any nodes, delete them
}
template <class Type>
void linkedListType<Type>::print() const
{
nodeType<Type> *current; //pointer to traverse the list
current = first; //set current so that it points to
//the first node
while (current != NULL) //while more data to print
{
cout << current->info << " ";
current = current->link;
}
}//end print
template <class Type>
int linkedListType<Type>::length() const
{
return count;
} //end length
template <class Type>
Type linkedListType<Type>::front() const
{
assert(first != NULL);
return first->info; //return the info of the first node
}//end front
template <class Type>
Type linkedListType<Type>::back() const
{
assert(last != NULL);
return last->info; //return the info of the last node
}//end back
template <class Type>
linkedListIterator<Type> linkedListType<Type>::begin()
{
linkedListIterator<Type> temp(first);
return temp;
}
template <class Type>
linkedListIterator<Type> linkedListType<Type>::end()
{
linkedListIterator<Type> temp(NULL);
return temp;
}
template <class Type>
void linkedListType<Type>::copyList
(const linkedListType<Type>& otherList)
{
nodeType<Type> *newNode; //pointer to create a node
nodeType<Type> *current; //pointer to traverse the list
if (first != NULL) //if the list is nonempty, make it empty
destroyList();
if (otherList.first == NULL) //otherList is empty
{
first = NULL;
last = NULL;
count = 0;
}
else
{
current = otherList.first; //current points to the list to be copied
count = otherList.count;
//copy the first node
first = new nodeType<Type>; //create the node
first->info = current->info; //copy the info
first->link = NULL; //set the link field of the node to NULL
last = first; //make last point to the first node
current = current->link; //make current point to
while (current != NULL)
{
newNode = new nodeType<Type>; //create a node
newNode->info = current->info; //copy the info
newNode->link = NULL; //set the link of newNode to NULL
last->link = newNode; //attach newNode after last
last = newNode; //make last point tothe actual last node
current = current->link; //make current point to the next node
}//end while
}//end else
}//end copyList
template <class Type>
linkedListType<Type>::~linkedListType() //destructor
{
destroyList();
}//end destructor
template <class Type>
linkedListType<Type>::linkedListType
(const linkedListType<Type>& otherList)
{
first = NULL;
copyList(otherList);
}//end copy constructor
//overload the assignment operator
template <class Type>
const linkedListType<Type>& linkedListType<Type>::operator=
(const linkedListType<Type>& otherList)
{
if (this != &otherList) //avoid self-copy
{
copyList(otherList);
}//end else
return *this;
}
#endif
他说我可以从主程序访问所有公共函数，并使用返回列表的第一个指针的函数来初始化当前指针。我该怎么做？
谢谢！
答案 0 :(得分：0)
啊，链表使用标准begin()函数，它给你一个迭代器。您的代码需要使用迭代器来遍历每个节点 - 您永远不会直接处理节点指针。
所以你的InList将从获取迭代器开始：
linkedListIterator<Payroll> iter = P.begin();
使用*iter
使用++iter
但在做这些事情之前，你必须确保你不在列表的末尾。要检查最后是否结束，您可以使用if(iter != P.end()) {...}
我现在暂时把它们放在一起 - 我不想破坏你的乐趣！
修改
看起来*iter可能不是访问Payroll对象的最佳方式。要访问Payroll成员，您应该能够使用->运算符。
像iter->info.getEmployeeNumber()
修改
使用它似乎不是一个好主意，但这是你可以添加到orderedLinkedList以从const引用中获取first的成员函数。
声明（在class orderedLinkedList ... {区内，在公共部分）：
const nodeType<Type>* GetHeadNode() const;
定义：
template <class Type>
const nodeType<Type>* orderedLinkedList<Type>::GetHeadNode() const {
return first;
}
您可能需要确保使用此指针在Payroll类中访问的任何成员函数也是const。如果你真的需要从const移除const nodeType<Type>*，它仍然有效。