我会非常感谢你的帮助。在我的计算机科学课上，我们被要求做一些我以前从未做过的事情，而且我不能很好地理解我的问题，甚至不知道谷歌的条款。
我们有三个文件。 lists.h，lists.cpp和driver.cpp
lists.h - 这是由教授提供的，不能被我改变。它是我将在......中推导出一个新类的基类。
lists.cpp - 这里我在类DLList中实现和双向链表。我之前做过dll，但不是这样。所以你会看到很多代码，尽管我无法测试任何代码。如果我的功能在这里错了，请不要担心，我只是想在......中创建一个双向链表。
driver.cpp - 这是我将用于在类DLList中测试我的函数的文件。
所以无论如何，我编译并得到......
g++ -c -g -Wall -std=c++11 driver.cpp
driver.cpp: In function ‘int main()’:
driver.cpp:12:5: error: ‘DLList’ was not declared in this scope
DLList<int> mylist;
^
我理解错误。我之前看过这个，当main没有看到函数/ class / etc时。在更简单的代码中，这是因为它是在main之后。但在这里，我只是不知道如何解决它。显然，driver.cpp无法在lists.cpp中看到我的代码。
这是我的代码 -
不可改变的lists.h
template<typename E> class List {
private:
void operator =(const List&) {} // Protect assignment
List(const List&) {} // Protect copy constructor
public:
List() {} // Default constructor
virtual ~List() {} // Base destructor
// Clear contents from the list, freeing memory
virtual void clear() = 0;
// Insert an element at the beginning of the list.
virtual void prepend(const E& item) = 0;
// Append an element at the end of the list.
virtual void append(const E& item) = 0;
// Extra credit: Insert an element at the current location, if possible;
// return true if successful, false if there is no current element
virtual bool insert(const E& item) = 0;
// Extra credit: Remove and assign to item the current element, if possible;
// return true if successful, false if there is no current element
virtual bool remove(E& item) = 0;
// Set the current position to the first element of the list, if possible;
// return true if successful, false if list was empty
virtual bool moveToStart() = 0;
// Set the current position to the last element of the list, if possible;
// return true if successful, false if list was empty
virtual bool moveToEnd() = 0;
// Move the current position one step right, if possible;
// return true if successful, false if already at the end
virtual bool next() = 0;
// Move the current position one step left, if possible;
// return true if successful, false if already at the beginning
virtual bool prev() = 0;
// Return a pointer to the current element (or NULL if none)
virtual const E* getValue() const = 0;
// Return total number of active nodes
virtual int numActive() = 0;
// Return total number of free nodes
virtual int numFree() = 0;
};
// Factory function
template<typename E> List<E> *createList();
lists.cpp
#include "lists.h"
#include <cstddef>
#include <iostream>
using namespace std;
// Doubly linked list link node with freelist support
template <typename E> class Link {
private:
// required by Lab 4
static int free; // # of nodes free
static int active; // # of nodes in use
static Link<E> *freelist; // Reference to freelist head
E element; // Value for this node
Link *next; // Pointer to next node in list
Link *prev; // Pointer to previous node
public:
// Constructors
Link(const E& it, Link *prevp=NULL, Link *nextp=NULL) {
element = it;
prev = prevp;
next = nextp;
}
Link(Link *prevp =NULL, Link *nextp =NULL) {
prev = prevp;
next = nextp;
}
void * operator new(std::size_t) { // Overloaded new operator
active++; // add to active count
if (freelist == NULL) { // Create space
return ::new Link; // ::new means use the standard c++ new operator
}
Link<E> *temp = freelist; // Can take from freelist
freelist = freelist->next;
free--; // will only subtract if we take from freelist
return temp; // Return the link
}
// Overloaded delete operator
void operator delete(void* ptr) {
free++;
active--;
// eliminate the Link being deleted from the active list
Link *prev_tmp=((Link<E>*)ptr)->prev;
Link *next_tmp=((Link<E>*)ptr)->next;
prev_tmp->next=next_tmp;
next_tmp->prev=prev_tmp;
((Link<E>*)ptr)->next = freelist; // Attach deleted Link to the head of the freelist
freelist = (Link<E>*)ptr; // Now redefine the freelist to the new head
}
E get_data() const {
return element;
}
E set_data(E& it) {
element=it;
}
Link<E> *get_next() const {
return next;
}
Link<E> *get_ptrb() const {
return prev;
}
void set_next(Link<E> *new_next ) {
next = new_next;
}
void set_prev(Link<E> *new_prev) {
prev = new_prev;
}
int get_free() {
return free;
}
int get_active(){
return active;
}
};
// The freelist head pointer is actually created here
template <typename E>
Link<E> *Link<E>::freelist = NULL;
template <typename E> class DLList: public List<E> {
private:
Link<E> *head; // Pointer to list header
Link<E> *tail; // Pointer to last element
Link<E> *curr; // Access to current element
void operator =(const DLList&) {} // Protect assignment
DLList(const DLList&) {} // Protect copy constructor
public:
// Default constructor
DLList() {
head=NULL;
tail=NULL;
}
// Base destructor
~DLList() {
//delete
}
// Clear contents from the DLList, freeing memory
void clear() = 0;
// Insert an element at the beginning of the DLList.
void prepend(const E& item) {
Link<E> *newLink = new Link<E>(item);
if (head==NULL) {
head=newLink;
tail=newLink;
curr=newLink;
}
else {
newLink->set_next(head);
head=newLink;
curr=newLink;
}
}
// Append an element at the end of the DLList.
void append(const E& item) {
Link<E> *newLink = new Link<E>(item);
if (head==NULL) {
head=newLink;
tail=newLink;
curr=newLink;
}
else {
tail->set_next(newLink);
tail=newLink;
curr=newLink;
}
}
void print_list() {
if (head==NULL) {
cout << "EMPTY LIST" << endl;
}
else {
Link<E> *temp_ptr = head;
int index=0;
while(temp_ptr) {
cout << "Link " << index++ << ": " << temp_ptr->get_data() << endl;
temp_ptr = temp_ptr->get_next();
}
}
}
// Extra credit: Insert an element at the current location, if possible;
// return true if successful, false if there is no current element
bool insert(const E& item) {
if (curr==NULL) {
return false;
}
else {
Link<E> *newLink = new Link<E>(item);
Link<E> *prev_ptr=curr->get_prev;
Link<E> *next_ptr=curr->get_next();
prev_ptr->set_next(curr);
curr->set_prev(prev_ptr);
next_ptr->set_prev(curr);
curr->set_next(next_ptr);
return true;
}
}
// Extra credit: Remove and assign to item the current element, if possible;
// return true if successful, false if there is no current element
bool remove(E& item) {
if (curr==NULL) {
return false;
}
else {
curr->set_data(item);
}
}
// Set the current position to the first element of the DLList, if possible;
// return true if successful, false if DLList was empty
bool moveToStart() {
if (head==NULL) {
return false;
}
else {
curr=head;
return true;
}
}
// Set the current position to the last element of the DLList, if possible;
// return true if successful, false if DLList was empty
bool moveToEnd() {
if (head==NULL) {
return false;
}
else {
curr=tail;
return true;
}
}
// Move the current position one step right, if possible;
// return true if successful, false if already at the end
bool next() {
if (curr==tail) {
return false;
}
else {
curr=curr->get_next();
return true;
}
}
// Move the current position one step left, if possible;
// return true if successful, false if already at the beginning
bool prev() {
if (curr==head) {
return false;
}
else {
curr=curr->get_prev();
return true;
}
}
// Return a pointer to the current element (or NULL if none)
const E* getValue() {
if (curr==NULL) {
return NULL;
}
else {
curr->get_data();
}
}
// ******** MIGHT HAVE TO GET THIS DATA FROM MULTIPLE SOURCES IF THE PTR IS NULL!!
// BUG !
// Return total number of active nodes
int numActive() {
return curr->get_active();
}
// ******** MIGHT HAVE TO GET THIS DATA FROM MULTIPLE SOURCES IF THE PTR IS NULL!!
// BUG !
// Return total number of free nodes
int numFree() {
return curr->get_free();
}
};
// Explicit instantiation
template List<int> *createList();
driver.cpp
#include <iostream>
#include "lists.h"
using namespace std;
void uppercaseify(string& mystr) {
for (auto& c: mystr)
c = toupper(c);
}
int main() {
createList<int>();
DLList<int> mylist;
return 0;
}
答案 0 :(得分：0)
你是对的，错误是因为你的驱动文件中没有声明DLList类型。修复它的最简单方法是将list.cpp文件包含在驱动程序文件中
#include "list.cpp"
通常，当您使用具有相同名称的.h和.cpp文件时，它们应引用同一个类。因此，如果您在类练习之外编写此示例，则可能将list.cpp文件命名为DLList.h（请注意，模板类应位于.h文件中）。
答案 1 :(得分：0)
我认为你不应该在main（）中显式实例化你的DLList类。这不起作用，因为你没有在“driver.cpp”中提供它的声明。
你应该做的是在“list.cpp”中实现工厂函数来返回动态分配的DLList实例：
template<> List<int> *createList() { return new DLList<int>; }
因此，对“driver.cpp”中的createList<int>()的调用将创建一个DLList实例，您可以通过List的界面进行测试：
int main() {
// Create a DLList through factory function.
List<int>* list = createList<int>();
// Use the DLList through the List interface.
list->append( ... );
// Finished with using list, free the memory
delete list; list = nullptr;
// Not necessary - we have created the DLList through factory function!
// DLList<int> mylist;
return 0;
}