c++ - 不完整类型

Question

我收到“下一个”和“上一个”变量的不完整类型错误。我不确定我做错了什么，因为我对用 C++ 编写类很生疏。任何帮助，将不胜感激!谢谢。

#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

执行文件:

#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 = 0;
}//ends LinearNode constructor

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

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

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

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

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

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

测试文件:

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

using namespace std;

int main()
{
    LinearNode node1, node2, move;
    node1.setElement(1);
    node2.setElement(2);

    node2.setNext(node1);
    node1.setPrevious(node2);

    move = node2;

    while(move.getNext() != NULL)
        cout << move.getElement() << endl;

}

Answer 1

您的类型具有递归定义，这是被禁止的。

class LinearNode
{
private: 
    LinearNode next;
    LinearNode previous;
};

数据成员next 和previous 是LinearNode 类的实例(不是引用或指针)，尚未完全定义。

你可能想要这个:

class LinearNode
{
private: 
    LinearNode * next;
    LinearNode * previous;
};