需要左值作为赋值的左操作数？在链接列表中添加Add_End，Delete和Delete_Front？

Question

我看过很多YouTube教程，但是他们都说相同的话。还有其他方法可以不同地链接节点，而不是“ prev-> Next（）= temp-> Next（）;” ？每次我使用它时，它都会显示相同的错误，即需要左值作为赋值的左操作数？请帮忙！这是代码。

#include <iostream>
using namespace std;


class Node {
public:
Node() {};
void SetData(int aData) { data = aData; };
void SetNext(Node* aNext) { next = aNext; };
int Data() { return data; };
Node* Next() { return next; };

private:
int data;
Node* next;
};

class List {
public:
List() {
    head = NULL;
    }
void Add_End(int data);
void Delete(int data);
void Delete_Front();
void Add_Front(int data);
void Delete_End();
Node* Find(int data);
void Print();

private:
Node *head;
};
void List::Add_End(int data) {
     Node* newNode = new Node();
     newNode->SetData(data);
     newNode->SetNext(NULL);
     if(head == NULL) {
        head = newNode;
        return;
    }
    Node *temp = head;
    while(temp->Next()!= NULL)
    {
    temp=temp->Next();
    }
    temp->SetNext(newNode);
    return;
}
void List::Delete(int data) {
   Node *prev = head;
   int i;
   if(data == 1){
        head = prev->Next();
        delete prev;
        return;
   }
    for(i = 0; i <(data-2);i=i+1){
        prev = prev->Next();
    }
    Node *temp = prev->Next();
    prev->Next()=temp -> Next();
    delete temp;
    return;
}
void List::Delete_Front() {
    if(head == NULL) {
    cout<<"List has no member so cannot delete front"<<endl;
    return;
    }
    delete head;
    head = head-> Next();
    return;
}
void List::Add_Front(int data) {
 Node* newNode = new Node();
 newNode->SetData(data);
 newNode->SetNext(head);
 head = newNode;
 return;
 }
void List::Delete_End() {
if(head == NULL) {
    cout<<"List has no member so cannot delete end"<<endl;
    return;
    }
if(head->Next() == NULL) {
    delete head;
    head = NULL;
    return;
    }
Node *current;
Node *prev;
prev = head;
for(current = head->Next(); current->Next() != NULL; current = current- >Next()) {
    prev = current;
    }
prev->SetNext(NULL);
delete current;
return;
}
Node* List::Find(int data) {
Node *current;
for(current = head; current!= NULL && current->Data() != data; current = current->Next())
    {}
if(current == NULL) {
    cout<<"Did not find "<<data<<"."<<endl;
    return  NULL;
}
else {
    cout<<"Found "<<data<<"."<<endl;
    return current;
}
}
void List::Print() {
Node *current;
cout<<"Linked List Nodes: "<<endl;
if(head == NULL){
    cout<<"List is empty." <<endl;
}
for(current = head; current != NULL; current = current->Next()){
    cout<<current->Data();
    cout<<endl;
}
return;
}
int main(){
List list;
Node *answer;
list.Add_End(111);
list.Print();
list.Add_End(222);
list.Print();
list.Add_End(333);
list.Print();
list.Add_End(444);
list.Print();
list.Add_End(555);
list.Print();
list.Delete(444);
list.Print();
list.Delete(333);
list.Print();
list.Delete(222);
list.Print();
list.Delete(555);
list.Print();
list.Delete(111);
list.Print();
list.Add_End(23);
list.Print();
list.Add_End(45);
list.Print();
list.Add_End(26);
list.Print();
list.Delete_Front();
list.Print();

cout<<"Testing Add_Front: and others"<<endl;
list.Add_Front(888);
list.Print();
list.Add_Front(999);
list.Print();
list.Add_Front(49);
list.Print();
cout<<"Checking find function"<<endl;
answer = list.Find(888);
cout<<"Value for node returned by find function call with 888 is " 
<<answer->Data()<<"."<<endl;
cout<<"Checking find function"<<endl;
answer = list.Find(999);
cout<<"Value for node returned by find function call with 999 is " 

cout<<"Checking find function"<<endl;
answer = list.Find(49);
cout<<"Value for node returned by find function call with 49 is "<<answer- 
      >Data()<<"."<<endl;
cout<<"Call find function with value not in list."<<endl;
answer = list.Find(7);

if(answer == NULL) {
    cout<<"returned null pointer since 7 not found"<<endl;
 }
else{
    cout<< "in else of answer == NULL where Value for node returned by 
find function call with 7 is "<<answer->Data()<<"."<<endl;
}
cout<<"testing delete_end: "<<endl;
list.Delete_End();
list.Print();
cout<<"testing delete_end: "<<endl;
list.Delete_End();
list.Print();
cout<<"testing delete_end: "<<endl;
list.Delete_End();
list.Print();
return 0;
}

Answer 1

这里的问题是Node的Next()方法返回next成员变量的副本，因此它成为一个r值（常量临时对象），不能在分配中用作l值。

这就是为什么它将错误抛出为lvalue required as left operand of assignment。

为了达到这个目的，您可以如下使用SetNext()类的Node方法：

prev->SetNext(temp->Next());

我希望这可以解决您的问题。

谢谢