[英]How do I properly use nested classes in my hpp file and cpp file?
我正在尝试使用迭代器实现单链表作为链表 class 的嵌套 class。 我遇到了很多我认为与使用迭代器有关的错误。 我花了几个小时研究这个，但不幸的是，很多解决方案都包含模板，我无法使用这些模板。 每次我解决一个问题时，都会出现一个新问题。
我的 cpp 文件中出现以下错误：
如果我弄清楚我的代码有什么问题，我将继续做更多的研究并在这里报告，希望能在其他人有同样的问题时提供帮助。
提前非常感谢！
这是我的 hpp 文件：
#ifndef linkedlist_h
#define linkedlist_h
class LinkedList {
public:
struct Node {
//Node(Node *aNext=nullptr) : next(aNext) {}
int value; //this is the value you want to save
Node *next; //this points to the next node in the list (or nullptr)
};
//friend class Iterator; //do Ineed this even though it's a nested class
Node *root;
//---------------------------------------------------------------
//add a NESTED Interator class...
class Iterator {
public:
Iterator(); //default constructor
Iterator(Node* aNode);//constructor
~Iterator(); //dtor
Iterator operator++();
Iterator operator++(int);
bool operator==(const Iterator &anIterator);
bool operator!=(const Iterator &anIterator);
int operator*();
operator Node*();
Node *current; //do I need to put LinkedList since it's a nested class?
//add all the necessary operators
protected:
};
//--------------------------------------------------------------
LinkedList(); //default constructor...
LinkedList(const LinkedList& aCopy); //copy ctor
~LinkedList(); //dtor
LinkedList& operator=(const LinkedList& aCopy); //assignment operator
void append(int value);
void prepend(int value);
void remove(int value);
int size(); //needs to return unsigned int????
Iterator begin();
Iterator end();
Iterator find(int value);
protected:
};
#endif /* linkedlist_h */
这是我的 cpp 文件：
#include <stdio.h>
#include "LinkedList.hpp"
//class Iterator;
LinkedList::LinkedList() {
root=nullptr;
}
LinkedList::LinkedList(const LinkedList& aCopy){ //copy ctor
Node *temp=aCopy.root;
Node *newNode = new Node;
root=newNode;
while (temp != nullptr){
newNode-> value=temp->value;
temp=temp->next;
if (temp !=nullptr){
newNode->next=new Node;
newNode=newNode->next;
}
else{ newNode->next=nullptr;}
}
}
LinkedList& LinkedList::operator=(const LinkedList &aCopy){ //assignment operator
while(root!=nullptr){
Node* oneBefore= root;
root =root->next;
delete oneBefore;
}
Node *newNode= new Node;
Node *temp=aCopy.root;
root=newNode;
while(temp!=nullptr){
newNode->value=temp->value;
temp=temp->next;
if(temp!=nullptr){
newNode->next=new Node;
newNode=newNode->next;
}
else{newNode->next=nullptr;}
}
return *this;
}
LinkedList::~LinkedList(){ //dtor
Node* oneBefore = nullptr;
while(root!=nullptr){
oneBefore=root;
root=root->next;
delete oneBefore;
}
}
void LinkedList::append(int value){
Node* newNode=new Node;
newNode->value=value;
if(root!=nullptr){
Node* temp = root;
while (temp->next !=nullptr){
temp=temp->next;
}
newNode->next=nullptr;
temp->next=newNode;
}
if(root==nullptr){
newNode->next=nullptr;
root=newNode;
}
}
void LinkedList::prepend(int value){
Node* newNode=new Node;
newNode->value=value;
if (root!=nullptr){
newNode->next=root;
root=newNode;
}
if(root==nullptr){
root=newNode;
newNode->next=nullptr;
}
}
void LinkedList::remove(int value){
if(root==nullptr){
Node *before=nullptr;
Node *temp=root;
if(temp->value==value){
root=temp->next;
}
else{
while(temp->value!=value &&temp->next != nullptr){
before=temp;
temp=temp->next;
}
if(temp->value==value){
before->next=temp->next;
}
}
delete temp;
}
}
int LinkedList::size(){
Node* aNode = root;
int numElements=0;
while(aNode!=nullptr){
aNode=aNode->next;
numElements=numElements+1;
}
return numElements;
}
LinkedList::Iterator LinkedList::begin(){
return LinkedList::Iterator(root);
}
LinkedList::Iterator LinkedList::end(){
Node *aNode=root;
while(aNode!=nullptr){
aNode=aNode->next;
}
return LinkedList::Iterator(aNode);
}
LinkedList::Iterator Iterator(){
current=nullptr;
}
LinkedList::Iterator(Node *aNode){
current=aNode;
}
LinkedList::Iterator operator++(){//I have no idea what the difference is supposed to be between this one and the one below
current=current->next;
return *this;
}
LinkedList::Iterator& Iterator::operator=(const LinkedList::Iterator& aCopy){ //assignment operator
current=aCopy.current;
return *this;
}
bool Iterator::operator !=(const LinkedList::Iterator& aCopy){
return current != aCopy.current;
}
bool Iterator::operator==(const LinkedList::Iterator& aCopy){
return current==aCopy.current;
}
int Iterator::operator*(){
return current->value;
}
更新：以下建议帮助很大：非常感谢！ 我遇到的最后一个错误是（我将在下面的编译器上标记它的显示位置）：-“隐式声明的复制赋值运算符的定义”
更新的 hpp 文件：
#ifndef linkedlist_h
#define linkedlist_h
class LinkedList {
public:
struct Node {
//Node(Node *aNext=nullptr) : next(aNext) {}
int value; //this is the value you want to save
Node *next; //this points to the next node in the list (or nullptr)
};
//friend class Iterator; //do Ineed this even though it's a nested class
Node *root;
//---------------------------------------------------------------
//add a NESTED Interator class...
class Iterator {
public:
Iterator();//default constructor
//Iterator() : current(nullptr) {}
Iterator(Node* aNode);
//Iterator(Node* aNode): current(aNode){};//constructor
~Iterator(); //dtor
Iterator operator++();
Iterator operator++(int);
bool operator==(const Iterator &anIterator);
bool operator!=(const Iterator &anIterator);
int operator*();
operator Node*();
Node *current; //do I need to put LinkedList since it's a nested class?
//add all the necessary operators
protected:
};
//--------------------------------------------------------------
LinkedList(); //default constructor...
LinkedList(const LinkedList& aCopy); //copy ctor
~LinkedList(); //dtor
LinkedList& operator=(const LinkedList& aCopy); //assignment operator
void append(int value);
void prepend(int value);
void remove(int value);
int size(); //needs to return unsigned int????
Iterator begin();
Iterator end();
Iterator find(int value);
protected:
};
#endif /* linkedlist_h */
更新的 cpp 文件：
#include <stdio.h>
#include "LinkedList.hpp"
//class Iterator;
LinkedList::LinkedList() {
root=nullptr;
}
LinkedList::LinkedList(const LinkedList& aCopy){ //copy ctor
Node *temp=aCopy.root;
Node *newNode = new Node;
root=newNode;
while (temp != nullptr){
newNode-> value=temp->value;
temp=temp->next;
if (temp !=nullptr){
newNode->next=new Node;
newNode=newNode->next;
}
else{ newNode->next=nullptr;}
}
}
LinkedList& LinkedList::operator=(const LinkedList &aCopy){ //assignment operator
while(root!=nullptr){
Node* oneBefore= root;
root =root->next;
delete oneBefore;
}
Node *newNode= new Node;
Node *temp=aCopy.root;
root=newNode;
while(temp!=nullptr){
newNode->value=temp->value;
temp=temp->next;
if(temp!=nullptr){
newNode->next=new Node;
newNode=newNode->next;
}
else{newNode->next=nullptr;}
}
return *this;
}
LinkedList::~LinkedList(){ //dtor
Node* oneBefore = nullptr;
while(root!=nullptr){
oneBefore=root;
root=root->next;
delete oneBefore;
}
}
void LinkedList::append(int value){
Node* newNode=new Node;
newNode->value=value;
if(root!=nullptr){
Node* temp = root;
while (temp->next !=nullptr){
temp=temp->next;
}
newNode->next=nullptr;
temp->next=newNode;
}
if(root==nullptr){
newNode->next=nullptr;
root=newNode;
}
}
void LinkedList::prepend(int value){
Node* newNode=new Node;
newNode->value=value;
if (root!=nullptr){
newNode->next=root;
root=newNode;
}
if(root==nullptr){
root=newNode;
newNode->next=nullptr;
}
}
void LinkedList::remove(int value){
if(root==nullptr){
Node *before=nullptr;
Node *temp=root;
if(temp->value==value){
root=temp->next;
}
else{
while(temp->value!=value &&temp->next != nullptr){
before=temp;
temp=temp->next;
}
if(temp->value==value){
before->next=temp->next;
}
}
delete temp;
}
}
int LinkedList::size(){
Node* aNode = root;
int numElements=0;
while(aNode!=nullptr){
aNode=aNode->next;
numElements=numElements+1;
}
return numElements;
}
LinkedList::Iterator LinkedList::begin(){
return LinkedList::Iterator(root);
}
LinkedList::Iterator LinkedList::end(){
Node *aNode=root;
while(aNode!=nullptr){
aNode=aNode->next;
}
return LinkedList::Iterator(aNode);
}
LinkedList::Iterator::Iterator() : current(nullptr) {}
LinkedList::Iterator::Iterator(Node* aNode): current(aNode){};
LinkedList::Iterator LinkedList::Iterator::operator++(){//I have no idea what the difference is supposed to be between this one and the one below
current=current->next;
return *this;
}
LinkedList::Iterator& LinkedList::Iterator::operator=(const LinkedList::Iterator& aCopy) noexcept{ //assignment operator; THIS IS WHERE I SEE AN ERROR
current=aCopy.current;
return *this;
}
bool LinkedList::Iterator::operator !=(const LinkedList::Iterator& aCopy){
return current != aCopy.current;
}
bool LinkedList::Iterator::operator==(const LinkedList::Iterator& aCopy){
return current==aCopy.current;
}
int LinkedList::Iterator::operator*(){
return current->value;
}
第一个问题（正如我在评论中已经说过的）是，嵌套 class 方法的定义应该看起来像LinkedList::Iterator::Iterator() {... }或bool LinkedList::Iterator::operator.=(...) {... } 。 （我只是在这里再写一次，以便更容易找到，如果其他人有同样的问题）
在赋值运算符的定义中出现错误的原因仅仅是因为您没有在 header 中为该 class 声明赋值运算符。
作为奖励回合： operator++()和operator++(int)之间的区别在于，第一个使用++a （前增量）调用，而另一个使用a++ （后增量）调用。 前增量还应该返回对相同 object 的引用（类似于 assingment 运算符），而后增量返回 object 的副本，就像它在增量之前一样。
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