如何解决如何在 LinkedList 类中实现迭代器类
刚接触 C++，我在 LinkedList 中实现 Iterator 类时遇到问题。我在 LinkedList 类的私有部分定义了一个 Iterator 类，如下所示：
cs_linked_list.h
#ifndef LINKED_LIST_H_
#define LINKED_LIST_H_
#include <initializer_list>
#include <iostream>
namespace cs {
template <typename T>
class LinkedList {
struct Node; // forward declaration for our private Node type
public:
/**Constructs an empty list.**/
LinkedList(){
head_ = nullptr;
}
/**
* @brief Constructs a list from a range.
*
*/
template <class InputIterator>
LinkedList(InputIterator first,InputIterator last) {
for (; first != last; ++first) this->push_back(*first);
}
/** Constructs a list with a copy of each of the elements in `init_list`,in the same order. */
LinkedList(std::initializer_list<T> init_list) {
this->operator=(init_list); // call initializer list assignment
}
/**Constructs a container with a copy of each of the elements in another,in the same order**/
LinkedList(const LinkedList<T>& another){
//Todo
this->operator=(another);
}
/** Destroys each of the contained elements,and deallocates all memory allocated by this list. */
~LinkedList() {
while (this->head_) {
Node* old_head = this->head_;
this->head_ = old_head->next;
delete old_head;
}
}
/**Returns the number of elements in this list.Node *head**/
size_t size() const{ //DONE
//Todo
Node *temp = head_;
size_t len = 0;
while (temp != nullptr){
len++;
temp = temp->next;
}
return len;
}
/**Returns whether the list container is empty (that is,whether its size is 0). **/
bool empty() const{ //DONE
if(size_ == 0){
return true;
} else{
return false;
}
}
/** Appends a copy of `val` to this list. */
void push_back(const T& val) {
Node* new_node = new Node{val};
if (this->size_ == 0) {
this->head_ = this->tail_ = new_node;
} else {
this->tail_->next = new_node;
new_node->prev = this->tail_;
this->tail_ = new_node;
}
++this->size_;
}
/** Prepends a copy of `val` to this list. */
void push_front(const T& val) {
Node* new_node = new Node{val};
if (this->size_ == 0) {
this->head_ = this->tail_ = new_node;
} else {
new_node->next = this->head_;
this->head_->prev = new_node;
this->head_ = new_node;
}
++this->size_;
}
/**Returns a reference to the value in the first element in this list.**/
T& front() const{
return head_->data;
}
/**Returns a reference to the value in the last element in this list. **/
T& back() const{
return tail_->data;
}
/**Deletes the first value in this list. **/
void pop_front(){
Node *temp = head_;
if(empty()){
return;
}
if(temp == tail_){
return;
}
head_ = head_->next;
if (head_ != nullptr) {
head_->prev = nullptr;
} else {
tail_ = nullptr;
}
delete temp;
}
/**Deletes the last value in this list**/
void pop_back(){
if(empty()){
return;
}
if(head_ == tail_){
return;
}
Node *temp = head_;
while(temp->next->next != nullptr){
temp = temp->next;
}
tail_ = temp;
delete tail_->next;
tail_->next = nullptr;
size_--;
}
/**resizes the list so that it contains n elements.**/
void resize(std::size_t n){
//Todo
for (size_t i = 0; i < n; i++){
push_back('\0');
}
}
/**resizes the list so that it contains n elements**/
void resize(std::size_t n,const T &fill_value){
//Todo
for (size_t i = 0; i < n; i++) {
push_back(fill_value);
}
}
/**Removes from the container all the elements that compare equal to val. **/
void remove(const T &val){
//Todo
Node *p1 = head_;
Node *p2 = nullptr;
if(p1 != nullptr && p1->data == val){
head_ = p1->next;
delete p1;
} else {
while (p1 != nullptr && p1->data != val){
p2 = p1;
p1 = p1->next;
}
if (p1 == nullptr) {
return;
}
p2->next = p1->next;
delete p1;
}
}
/**Removes duplicate values from this list**/
void unique(){
//Todo
Node *temp = head_;
while (temp != nullptr && temp->next != nullptr) {
Node *temp2 = temp;
while (temp2->next != nullptr) {
if (temp->data == temp2->next->data) {
Node *temp3 = temp2->next;
temp2->next = temp2->next->next;
delete temp3;
} else {
temp2 = temp2->next;
}
}
temp = temp->next;
}
}
/**Deletes all values in this list.**/
void clear(){
//Todo
while (head_ != nullptr){
Node *temp = head_;
head_ = head_->next;
delete temp;
}
tail_ = nullptr;
size_ = 0;
}
/**Reverses the order of the elements in this list.**/
void reverse(){
//Todo
Node *p1 = head_;
Node *p2 = nullptr;
while (p1 != nullptr) {
Node *temp = p1->next;
p1->next = p2;
p2 = p1;
p1 = temp;
}
head_ = p2;
}
/** Replaces the contents of this list with a copy of each element in `init_list`. */
LinkedList& operator=(std::initializer_list<T> init_list) {
this->size_ = 0;
for (auto&& val : init_list)
this->push_back(val);
return *this;
}
/**Replaces the contents of this list with a copy of each element in another,in the same order.**/
LinkedList& operator=(const LinkedList& another){
//Todo
if (this != &another) {
this->clear();
Node *temp = another.head_;
this->size_ = 0;
while (temp) {
this->push_back(temp->data);
temp = temp->next;
}
}
return *this;
}
/**Compares this list with another for equality.**/
bool operator==(const LinkedList &another){ //DONE
//Todo
auto comp = head_;
auto comp2 = another.head_;
while(comp != nullptr){
if(comp != comp2){
return false;
}
comp = comp->next;
comp2 = comp2->next;
}
return true;
}
/**Compares this list with another for inequality. **/
bool operator!=(const LinkedList &another){ //DONE
//Todo
auto comp = head_;
auto comp2 = another.head_;
while(comp != nullptr){
if(comp != comp2){
return true;
}
comp = comp->next;
comp2 = comp2->next;
}
return false;
}
/** Inserts this list into an ostream,with the format `[element1,element2,element3,...]` */
friend std::ostream& operator<<(std::ostream& out,const LinkedList& list) {
out << '[';
for (Node* cur = list.head_; cur; cur = cur->next) {
out << cur->data;
if (cur->next)
out << ",";
}
out << ']';
return out;
}private:
struct Node {
T data;
Node* next = nullptr;
Node* prev = nullptr;
};
Node* head_ = nullptr;
Node* tail_ = nullptr;
std::size_t size_ = 0;
class Iterator {
public:
using iterator_category = std::bidirectional_iterator_tag;
using value_type = T;
using difference_type = int;
using pointer = T*;
using reference = T&;
// Default constructor
Iterator() {
//Todo
n = nullptr;
}
// copy constructor
Iterator(const Iterator& other) {
//Todo
this->operator=(other);
}
//Destructor if needed
~Iterator() {
//Todo
while (this->list.head_){
Node *old_head = this->list.head_;
this->list.head_ = old_head->next;
delete old_head;
}
}
// copy assign
Iterator& operator=(const Iterator& that) {
//Todo
if(this != &that){
this->list.clear();
Node *temp = that.list.head_;
this->list.size_ = 0;
while (temp){
this->list.push_back(temp->data);
temp = temp->next;
}
}
return *this;
}
// Prefix increment
Iterator& operator++() {
//Todo
this->n = this->n->next;
return *this;
}
// Postfix increment
Iterator operator++(int) {
Iterator tmp(*this);
this->operator++();
return tmp;
}
// Prefix decrement
Iterator& operator--() {
//Todo
this->n = this->n->prev;
return *this;
}
// Postfix decrement
Iterator operator--(int) {
Iterator tmp(*this);
this->operator--();
return tmp;
}
// Inequality
bool operator!=(Iterator that) const {
return !(this->operator==(that));
}
// Equality
bool operator==(Iterator that) const {
//Todo
auto temp = list.head_;
auto temp2 = that.list.head_;
while(temp != nullptr){
if(*temp != *temp2){
return false;
}
temp = temp->next;
temp2 = temp2->next;
}
return true;
}
// lvalue dereference
T& operator*() const {
//Todo
return this->n->data;
}
// referring
Iterator* operator->() const {
return this;
}
Iterator begin(){
//Todo
return Iterator(list.head_->next);
}
Iterator end(){
//Todo
return Iterator(list.tail_);
}
private:
Node *n;
LinkedList<T> list;
};
};
} // namespace cs
#endif // LINKED_LIST_H_
主要内容：
#include "cs_linked_list.h"
#include <iostream>
int main() {
/***TESTING***/
cs::LinkedList<int> list;
// Add few items to the end of LinkedList
list.push_back(1);
list.push_back(2);
list.push_back(3);
std::cout << "Traversing LinkedList through Iterator" << std::endl;
for ( cs::LinkedList<int>::Iterator iter = list.begin();iter != list.end(); iter++) {
std::cout << *iter << " ";
}
std::cout << std::endl;
return 0;
}
由于我的 Iterator 类是私有的，我似乎无法实现我的 Begin() 和 End() 函数。我应该公开它还是我错过了关键的一步。说明说在我的 LinkedList 类的私有部分定义一个 Iterator 类。
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