我编写了List模板的实现方式，其作用类似于std :: list。这是一个 List.h 文件：
#include <memory>
template<typename T>
class List {
class Node {
public:
T data;
Node *previous;
Node *next; //is that T needed?
Node(T &d, Node *p, Node *n) : data(d), next(n) { };
};
private:
Node *head; //first element
Node *tail;
void create() { head = tail = NULL; }
void create(const List &rhs);
void uncreate();
public:
typedef T *iterator;
typedef const T *const_iterator;
typedef size_t size_type;
typedef T value_type;
List() { create(); };
List &operator=(const List &rhs);
List(const List &rhs) { create(rhs); };
~List() { uncreate(); };
T *begin() { return head->data; };
T *end() { return tail->next->data; };
T front() { return head->data; };
T back() { return tail->data; };
bool empty() {return head==NULL;}
size_type size() { return tail - head + 1; }; //add one here?
T &operator[](size_type i);
// const T &operator[](size_type i) const; //how to implement and do not duplicate code?
T *push_back(T &data);
T *push_front(T &data);
void pop_front();
void pop_back();
};
这是我的 List.cpp 文件
#include "List.h"
#include <cassert>
#include <iterator>
template<typename T, class Node>
class iterator : public std::iterator<std::bidirectional_iterator_tag, Node*, Node&>{
Node* underlying;
public:
explicit iterator(Node *n):underlying(n){};
iterator():underlying(nullptr){};
iterator& operator++() { //preinc
assert(underlying != nullptr && "Out-of-bounds iterator increment!");
underlying = underlying->next;
return *this;
}
iterator operator++(int) { //postinc
assert(underlying != nullptr && "Out-of-bounds iterator increment!");
iterator temp(*this);
++(*this);
return temp;
}
iterator& operator--() { //predec
assert(underlying != nullptr && "Out-of-bounds iterator decrement!");
underlying = underlying->previous;
return *this;
}
iterator operator--(int) { //postdec
assert(underlying != nullptr && "Out-of-bounds iterator decrement!");
iterator temp(*this);
--(*this);
return temp;
}
bool operator== (const iterator& rhs)
{
return underlying == rhs.underlying;
}
bool operator!= (const iterator& rhs)
{
return underlying != rhs.underlying;
}
T& operator*() {
return underlying->data;
}
};
void List::create(const List &rhs) {
iterator this_iter = head;
iterator rhs_iter = rhs.head;
while(rhs_iter!=NULL){
this_iter->data = (rhs_iter++)->data;
++this_iter;
}
}
List::value_type &List::operator[](List::size_type i) {
if (i < size() && i >= 0) {
Node *temp = head;
while (i > 0) {
temp = temp->next;
i--;
}
return temp->data;
}
throw std::out_of_range("Index out of range");
}
List &List::operator=(const List &rhs) {
if (&rhs != this) {
uncreate();
create(rhs);
}
return *this;
}
List::value_type *List::push_back(List::value_type &data) {
Node *n = new Node(data, tail, 0);
tail->next = n;
tail = tail->next;
if(head==0) //if it was the first element added
head = tail;
return tail;
}
List::value_type *List::push_front(List::value_type &data) {
Node *n = new Node(data, 0, head);
head->previous = n;
head = n;
if(tail==0) //if it was the first element added
tail = head;
return head;
}
void List::pop_front() {
Node* new_head = head->next;
delete head->data; //delete, erase or what?
head = new_head;
}
void List::pop_back() {
delete tail->data; //delete, erase or what?
tail = tail->previous;
}
void List::uncreate() {
Node* temp = head;
while(temp!=NULL){
delete temp->data;
temp = temp->next;
}
head = tail = NULL;
}
我还创建了一个简单的main.cpp：
#include "List.h"
int main(){
List<int> l;
l.push_back(1);
l.push_back(2);
l.push_back(3);
}
但是我遇到了很多错误：
main.cpp:5:5: error: ‘l’ was not declared in this scope
l.push_back(1);
^
List.cpp:58:11: error: ‘T’ was not declared in this scope
void List<T>::create(const List &rhs) {
^
List.cpp:58:12: error: template argument 1 is invalid
void List<T>::create(const List &rhs) {
^
List.cpp:58:28: error: invalid use of template-name ‘List’ without an argument list
void List<T>::create(const List &rhs) {
^
List.cpp: In function ‘void create(const int&)’:
List.cpp:59:14: error: missing template arguments before ‘this_iter’
iterator this_iter = head;
^
List.cpp:60:14: error: missing template arguments before ‘rhs_iter’
iterator rhs_iter = rhs.head;
^
List.cpp:61:11: error: ‘rhs_iter’ was not declared in this scope
while(rhs_iter!=NULL){
^
List.cpp:62:9: error: ‘this_iter’ was not declared in this scope
this_iter->data = (rhs_iter++)->data;
^
List.cpp: At global scope:
List.cpp:67:1: error: invalid use of template-name ‘List’ without an argument list
List::value_type &List::operator[](List::size_type i) {
^
List.cpp:79:1: error: invalid use of template-name ‘List’ without an argument list
List &List::operator=(const List &rhs) {
^
List.cpp:88:1: error: invalid use of template-name ‘List’ without an argument list
List::value_type *List::push_back(List::value_type &data) {
^
List.cpp:97:1: error: invalid use of template-name ‘List’ without an argument list
List::value_type *List::push_front(List::value_type &data) {
^
List.cpp:107:6: error: ‘template<class T> class List’ used without template parameters
void List::pop_front() {
^
List.cpp: In function ‘void pop_front()’:
List.cpp:108:5: error: ‘Node’ was not declared in this scope
Node* new_head = head->next;
^
List.cpp:108:11: error: ‘new_head’ was not declared in this scope
Node* new_head = head->next;
^
List.cpp:108:22: error: ‘head’ was not declared in this scope
Node* new_head = head->next;
^
List.cpp: At global scope:
List.cpp:113:6: error: ‘template<class T> class List’ used without template parameters
void List::pop_back() {
^
List.cpp: In function ‘void pop_back()’:
List.cpp:114:12: error: ‘tail’ was not declared in this scope
delete tail->data; //delete, erase or what?
^
List.cpp: At global scope:
List.cpp:118:6: error: ‘template<class T> class List’ used without template parameters
void List::uncreate() {
^
List.cpp: In function ‘void uncreate()’:
List.cpp:119:5: error: ‘Node’ was not declared in this scope
Node* temp = head;
^
List.cpp:119:11: error: ‘temp’ was not declared in this scope
Node* temp = head;
^
List.cpp:119:18: error: ‘head’ was not declared in this scope
Node* temp = head;
^
List.cpp:124:12: error: ‘tail’ was not declared in this scope
head = tail = NULL;
我知道我的实现不起作用，但我甚至无法检查出错是什么，因为我无法运行它。谁能帮我解决一下呢？
答案 0 :(得分：2)
void List::create(const List &rhs) {
...
}
您必须将template添加到列表定义
template<typename T>
void List<T>::create(const List<T> &rhs) {
...
}
您已声明
T *push_back(T &data);
但后来定义为
List::value_type *List::push_back(List::value_type &data)
{
...
}
修复它的简单方法是将声明和定义放在一起。因此，请将T *push_back(T &data);更改为：
T *push_back(T &data)
{
Node *n = new Node(data, tail, 0);
tail->next = n;
tail = tail->next;
if (head == 0) //if it was the first element added
head = tail;
return tail;
}
编辑：
即使这个编译它还有许多其他错误和泄漏。以下是List
定义复制构造函数和赋值运算符还需要做更多的工作。他们必须使用List::push_back复制其他列表。目前我们无法访问它们（通过将它们声明为私有），因此不会意外使用它们。
template<typename T>
class List
{
private:
List &operator=(const List &rhs);
List(const List &rhs);
public:
class Node
{
public:
T data;
Node *prev, *next;
Node(T dataT)
{
data = dataT;
next = prev = NULL;
};
};
protected:
Node *head, *tail;
public:
Node *get_head() { return head; };
Node *get_tail() { return tail; };
List()
{
head = tail = NULL;
};
~List()
{
while (head)
remove(head);
};
//Node *push_back(T dataT) //use this for older compilers
Node *push_back(const T &&dataT) //for C++ 14
{
Node *node = new Node(dataT);
if (head == NULL)
{
//adding first item to list
head = tail = node;
}
else
{
//adding item to end of the list
node->prev = tail;
tail->next = node;
tail = node;
}
return node;
}
void remove(Node *node)
{
if (!node) return;
if (node == tail && node == head)
{
//deleting the only node, nothing will be left
head = tail = NULL;
}
else if (node == tail)
{
tail = node->prev;
tail->next = NULL;
}
else if (node == head)
{
head = node->next;
head->prev = NULL;
}
else
{
//deleting a node in the mid
node->prev->next = node->next;
node->next->prev = node->prev;
}
delete node;
}
size_t size()
{
size_t i = 0;
Node *node = head;
while (node)
{
node = node->next;
i++;
}
return i;
}
T &operator[](size_t i);
};
用法：
int main()
{
List<int> list;
list.push_back(1);
list.push_back(2);
list.push_back(3);
for (size_t i = 0; i < list.size(); i++)
std::cout << list[i] << "\n";
}