指针编译器问题

Question

我已经三年多没有使用过指针了，而且我对这个话题非常生疏。当我编译以下代码时，我收到了大量错误。错误如下：

 ubuntu@ubuntu:~/Desktop/stuff$ g++ test.cpp LinearNode.cpp LinkedList.cpp 

 LinkedList.cpp: In member function ‘void LinkedList::add(int)’:

 LinkedList.cpp:26: error: request for member ‘getElement’ in ‘((LinkedList*)this)->LinkedList::contents’, which is of non-class type ‘LinearNode*’

 LinkedList.cpp:31: error: request for member ‘getNext’ in ‘((LinkedList*)this)->LinkedList::contents’, which is of non-class type ‘LinearNode*’

 LinkedList.cpp:39: error: request for member ‘setPrevious’ in ‘((LinkedList*)this)->LinkedList::contents’, which is of non-class type ‘LinearNode*’

 LinkedList.cpp:40: error: cannot convert ‘LinearNode’ to ‘LinearNode*’ in assignment

 LinkedList.cpp: In member function ‘int LinkedList::remove(int)’:

 LinkedList.cpp:60: error: request for member ‘getElement’ in ‘((LinkedList*)this)->LinkedList::contents’, which is of non-class type ‘LinearNode*’

 LinkedList.cpp:62: error: request for member ‘getElement’ in ‘((LinkedList*)this)->LinkedList::contents’, which is of non-class type ‘LinearNode*’

 LinkedList.cpp:63: error: request for member ‘getNext’ in ‘((LinkedList*)this)->LinkedList::contents’, which is of non-class type ‘LinearNode*’

 LinkedList.cpp:67: error: invalid conversion from ‘LinearNode*’ to ‘int’

 LinkedList.cpp:67: error:   initializing argument 1 of ‘LinearNode::LinearNode(int)’

 LinkedList.cpp:68: error: request for member ‘getNext’ in ‘((LinkedList*)this)->LinkedList::contents’, which is of non-class type ‘LinearNode*’
 LinkedList.cpp: In member function ‘void LinkedList::print()’:
 LinkedList.cpp:97: error: invalid conversion from ‘LinearNode*’ to ‘int’
 LinkedList.cpp:97: error:   initializing argument 1 of ‘LinearNode::LinearNode(int)’

Linked List.h:

#ifndef LINKEDLIST_H
#define LINKEDLIST_H
#include<iostream>
#include"LinearNode.h"

using namespace std;

class LinearNode;

class LinkedList
{
    public:
        LinkedList();
        void add(int element);
        int remove (int element);
        void print();

    private:
        int count;
        LinearNode* contents;
};//ends the class linked list

#endif

Linked List:

#include<iostream>
#include"LinearNode.h"
#include"LinkedList.h"

using namespace std;

//linkedlist constructor for an empty linked list
LinkedList::LinkedList()
{
    count = 0;
    contents = NULL;
}//ends the constructor

//adds an element to the front of the linked list
void LinkedList::add(int element)
{
    int found = 0, current = 0;

    for (int index = 0; index < count; index++)
    {
        if (contents.getElement() == element)
            found = 1;
        else    
        {

            contents = *contents.getNext();
        }//ends the else statement
    }//ends the while loop

    if (found == 0)
    {
        LinearNode node(element);
        node.setNext(contents);
        contents.setPrevious(&node);
        contents = node;
        count++;

//print();
cout << endl;

    }//ends the found == 0 if statment
}//ends the add function

//this function removes one element from the linked list.
int LinkedList::remove(int element)
{
    int found = 0, result = 0; 
    LinearNode previous;
    LinearNode current;

    if (count == 0)
        cout << "The list is empty" << endl;
    else 
    {
        if (contents.getElement() == element)
        {
            result = contents.getElement();
            contents = *contents.getNext();
        }//ends the contents.getElement() == element
        else 
        {
            previous = contents;
            current = *contents.getNext();
            for (int index = 0; ( (index < count) && (found == 0) ); index++)
                if (current.getElement() == element)
                    found = 1;
                else
                {
                    previous = current;
                    current = *current.getNext();
                }//ends the else statement 

            if (found == 0)
                cout << "The element is not in the list" << endl;
            else
            {
                result = current.getElement();
                previous.setNext(current.getNext());
            }//ends else statement  

        }//ends the else stamtement

        count--;
    }//ends the else statement of count == 0
    return result;
}//ends the remove function


void LinkedList::print()
{
    LinearNode current;
    current = contents; 

    for (int index = 0; index < count; index++)
    {
        cout << current.getElement() << endl;
        current = *current.getNext();
    }//ends the for loop
}//ends Print function

LinearNode.h:

 #ifndef LINEARNODE_H
#define LINEARNODE_H

#include<iostream>

using namespace std;

class LinearNode
{
    public:
        //Constructor for the LinearNode class that takes no arguments 
        LinearNode();
        //Constructor for the LinearNode class that takes the element as an argument
        LinearNode(int el);
        //returns the next node in the set.
        LinearNode* getNext();
        //returns the previous node in the set
        LinearNode* getPrevious();
        //sets the next element in the set
        void setNext(LinearNode* node);
        //sets the previous element in the set
        void setPrevious(LinearNode* node);
        //sets the element of the node
        void setElement(int el);
        //gets the element of the node
        int getElement();

    private: 
        LinearNode* next;
        LinearNode* previous;
        int element;        
};//ends the LinearNode class

#endif

LinearNode:

 #include<iostream>
#include"LinearNode.h"

using namespace std;

//Constructor for LinearNode, sets next and element to initialized states
LinearNode::LinearNode()
{
    next = NULL;
    element = 0;
}//ends LinearNode default constructor

//Constructor for LinearNode takes an element as argument.
LinearNode::LinearNode(int el)
{
    next = NULL;
    previous = NULL;
    element = el;
}//ends LinearNode constructor

//returns the next element in the structure
LinearNode* LinearNode::getNext()
{
    return next;
}//ends getNext function

//returns previous element in structure
LinearNode* LinearNode::getPrevious()
{
    return previous;
}//ends getPrevious function

//sets the next variable for the node
void LinearNode::setNext(LinearNode* node)
{
    next = node;
}//ends the setNext function

//sets previous for the node
void LinearNode::setPrevious(LinearNode* node)
{
    previous = node;
}//ends the setPrevious function

//returns element of the node
int LinearNode::getElement()
{
    return element;
}//ends the getelement function

//sets the element of the node
void LinearNode::setElement(int el)
{
    element = el;
}//ends the setElement function

Answer 1

这里有许多单独的错误，但关于指针的错误是您使用点 (.) 来访问指向类的指针的成员。点用于访问类对象的成员（而不是指针）。您应该使用箭头 (->) 来访问类指针的成员。

例如，

if (contents.getElement() == element)

应该是

if (contents->getElement() == element)

Answer 2

由于您使用的是 contents 指针，因此您需要正确引用它才能访问成员。例如，第一个错误是由 LinkedList::add 引起的：

void LinkedList::add(int element)
{
    int found = 0, current = 0;

    for (int index = 0; index < count; index++)
    {
        // This is your first error
        //if (contents.getElement() == element)

        // Change to:
        if (contents->getElement() == element)
            found = 1;

Answer 3

. 的优先级高于 *。所以改成

contents = *contents.getNext();

并且

contents = (*contents).getNext();

你必须在多个地方纠正它。

如果您需要摆脱所有这些，只需使用 -

contents = contents->getNext();