编译C ++链表时未定义的引用

Question

因此，我已经搜索过Google，Binged，并且尝试了许多不同的潜在修复程序，但仍然无法弄清为什么我的链接列表实现无法编译。我知道这与我的班级名称有关，但是就我所知。我最初将标头拆分为不同的子文件夹，但现在我将其全部放在同一文件夹中只是为了编译内容。我承认，自从本科毕业以来，我在C ++中没有做太多事情，但这就是为什么我试图清除这些蜘蛛网的一部分。任何建议将不胜感激。我附上下面的代码。这是我当前的gcc编译命令：

g++ main.cpp list.cpp -o llist

list.h

#ifndef TEO_LIST_H
#define TEO_LIST_H
#include <iostream>

template<typename T>
struct Node {
    public:
        T data;
        Node<T>* next;
        Node<T>* prev;
};

template<class T>
class List {
    private:
        int length;
        Node<T>* head;
        Node<T>* tail;
        Node<T>* curr;

    public:
        // Constructors
        List();

        int Length();

        // Node Access
        Node<T>* NextNode();
        Node<T>* PrevNode();

        // Node Actions
        void InsertAfter(Node<T>* ptr);
        void InsertBefore(Node<T>* ptr);
        Node<T>* DeleteAfter();
        Node<T>* DeleteBefore();
        void StepNext();
        void StepPrev();
        void StepHead();
        void StepTail();

        // Expose List Data
        bool IsHead();
        bool IsTail();
        T Data();
};

#endif

list.cpp

#include "list.h"

template<class T>
List<T>::List() {
    length = 0;
    head = NULL;
    tail = NULL;
    curr = NULL;
}

template<class T>
int List<T>::Length() {
    return this.length;
}

template<class T>
Node<T>* List<T>::NextNode() {
    return this.curr->next;
}

template<class T>
Node<T>* List<T>::PrevNode() {
    return this.curr->prev;
}

/*  This method inserts a node after the current position in the list.  */
template<class T>
void List<T>::InsertAfter(Node<T>* ptr) {
    if (this.length = 0) {
        // Insert first node in the list
        this.head = ptr;
        this.tail = ptr;
        this.curr = ptr;
    }
    else {
        // Insert a new node in an existing list
        // Set the new links moving forward (curr -> ptr -> next)
        ptr->next = this.curr->next;
        this.curr->next = ptr;

        // Set the new links moving backward (next -> ptr -> curr)
        if (ptr->next != NULL) // ptr = tail
            ptr->next->prev = ptr;
        ptr->prev = this.curr;
    }

    this.length++;
}

/*  This method inserts a node before the current position in the list.  */
template<class T>
void List<T>::InsertBefore(Node<T>* ptr) {
    if (this.length = 0) {
        // Insert first node in the list
        this.head = ptr;
        this.tail = ptr;
        this.curr = ptr;
    }
    else {
        // Set the new links moving forward (prev -> ptr -> curr)
        ptr->prev = this.curr->prev;
        this.curr->prev = ptr;

        // Set the new links moving backward (curr -> ptr -> prev)
        if (ptr->prev != NULL) // ptr = head
            ptr->prev->next = ptr;
        ptr->next = this.curr;
    }

    this.length++;
}

/*  This method deletes the next node from the list and returns the deleted node.
    If the next node is NULL (aka: curr = tail) do nothing and return NULL.  */
template<class T>
Node<T>* List<T>::DeleteAfter() {
    // Get the node we are about to delete.
    Node<T>* tmpNode = this.curr->next;

    if (this.length > 0) // Don't deprecate if in an empty list.
        this.length--;

    // Per our spec, if tmpNode is NULL, we are at the tail and will return NULL.
    if (tmpNode = NULL) return NULL;

    // Remove the link to tmpNode moving forward
    this.curr->next = tmpNode->next;
    // Remove the link to tmpNode moving backward
    if (tmpNode->next != NULL) // tmpNode = tail
        tmpNode->next->prev = this.curr;

    return tmpNode;
}

/*  This method deletes the prev node from the list and returns the deleted node.
    If the prev node is NULL (aka: curr = head) do nothing and return NULL.  */
template<class T>
Node<T>* List<T>::DeleteBefore() {
    // Get the node we are about to delete.
    Node<T>* tmpNode = this.curr->prev;
    if (this.length > 0) // Don't deprecate if in an empty list.
        this.length--;

    // Per our spec, if tmpNode is NULL, we are at the head and will return NULL.
    if (tmpNode = NULL) return NULL;

    // Remove the link to tmpNode moving backward
    this.curr->prev = tmpNode->prev;
    // Remove the link to tmpNode moving forward
    if (tmpNode->prev != NULL) // tmpNode = head
        tmpNode->prev->next = this.curr;

    return tmpNode;
}

/*  This method moves forward in the list.
    If the next node is NULL, we are at the tail and don't move forward.  */
template<class T>
void List<T>::StepNext() {
    if (this.curr->next != NULL) this.curr = this.curr->next;
}

/*  This method moves forward in the list.
    If the prev node is NULL, we are at the head and don't move backward.  */
template<class T>
void List<T>::StepPrev() {
    if (this.curr->prev != NULL) this.curr = this.curr->prev;
}

/*  This method moves to the head of the list.  */
template<class T>
void List<T>::StepHead() {
    this.curr = this.curr->head;
}

/*  This method moves to the tail of the list.  */
template<class T>
void List<T>::StepTail() {
    this.curr = this.curr->tail;
}

/*  This method returns true if curr = head and false otherwise.  */
template<class T>
bool List<T>::IsHead() {
    if (this.curr->prev = NULL)
        return true;
    else
        return false;
}

/*  This method returns true if curr = tail and false otherwise.  */
template<class T>
bool List<T>::IsTail() {
    if (this.curr->next = NULL)
        return true;
    else
        return false;
}

/*  This method returns curr.data.  */
template<class T>
T List<T>::Data() {
    return this.curr.data;
}

main.cpp

#include <iostream>
#include "list.h"

int main(int argc, char *argv[]) {
    List<int> *linkedList = new List<int>();
    Node<int> *a, *b, *c;

    a->data = 1013;
    b->data = 711;
    c->data = 1202;

    linkedList->InsertAfter(a);
    linkedList->InsertBefore(b);
    linkedList->StepNext(); // curr = a
    linkedList->InsertAfter(c);

    linkedList->StepHead();
    std::cout << "Traversing forward..." << std::endl;
    while (!linkedList->IsTail()) {
        std::cout << "Current Node Value: " << linkedList->Data() << std::endl;
        linkedList->StepNext();
    }

    linkedList->StepTail();
    std::cout << "Traversing backward..." << std::endl;
    while (!linkedList->IsHead()) {
        std::cout << "Current Node Value: " << linkedList->Data() << std::endl;
        linkedList->StepPrev();
    }

    return 0;
}

编译错误

/usr/bin/ld: /tmp/ccjGuq0i.o: in function `main':
main.cpp:(.text+0x23): undefined reference to `List<int>::List()'
/usr/bin/ld: main.cpp:(.text+0x58): undefined reference to `List<int>::InsertAfter(Node<int>*)'
/usr/bin/ld: main.cpp:(.text+0x6b): undefined reference to `List<int>::InsertBefore(Node<int>*)'
/usr/bin/ld: main.cpp:(.text+0x77): undefined reference to `List<int>::StepNext()'
/usr/bin/ld: main.cpp:(.text+0x8a): undefined reference to `List<int>::InsertAfter(Node<int>*)'
/usr/bin/ld: main.cpp:(.text+0x96): undefined reference to `List<int>::StepHead()'
/usr/bin/ld: main.cpp:(.text+0xca): undefined reference to `List<int>::IsTail()'
/usr/bin/ld: main.cpp:(.text+0xf3): undefined reference to `List<int>::Data()'
/usr/bin/ld: main.cpp:(.text+0x11e): undefined reference to `List<int>::StepNext()'
/usr/bin/ld: main.cpp:(.text+0x12c): undefined reference to `List<int>::StepTail()'
/usr/bin/ld: main.cpp:(.text+0x160): undefined reference to `List<int>::IsHead()'
/usr/bin/ld: main.cpp:(.text+0x189): undefined reference to `List<int>::Data()'
/usr/bin/ld: main.cpp:(.text+0x1b4): undefined reference to `List<int>::StepPrev()'
collect2: error: ld returned 1 exit status