求教，这个单链表为什么getData函数出有关问题

#include "Student.h"
#include <iostream>
using namespace std;
template<class T>
class linkNode{
public:
    linkNode(linkNode<T>* ptr=NULL){
        link=ptr;
    }
    linkNode(T& x,linkNode<T>* ptr=NULL){
        data=x;
        link=ptr;
    }

    T* data;
    linkNode* link;
};
template<class T>
class List:public linkNode<T>{
protected:
    linkNode<T>* first;
public:
    List();
    List(T& x);
    List(List<T>& L);
    ~List();
    void makeEmpty();
    int length();
    linkNode<T>* getHead();
    linkNode<T>* search(T& x);
    linkNode<T>* locate(int i);
    bool getData(int i,T& x);
    void setData(int i,T& x);
    bool insert(int i,T& x);
    bool remove(int i,T& x);
    bool isEmpty();
    void sort();
    List<T>&operator==(List<T>& L);
    List<T>&reverse(List<T>& L);
};
template<class T>
List<T>::List(){
    first=new linkNode<T>();
}
template<class T>
List<T>::List(T& x){
    first=new linkNode<T>(x);
}
template<class T>
List<T>::List(List<T>& L){
    List<T>* newList;
    linkNode<T>* newNode;
    linkNode<T>* current;
    current=first->link;
    newList->first=first;
    while (current->link!=NULL)
    {
        newNode->data=current->data;
        newNode->link=current->link;
        current=current->link;
        newNode=newNode->link;
    }

}
template<class T>
List<T>::~List(){
    makeEmpty();
}
template<class T>
void List<T>::makeEmpty(){
    linkNode<T>* del;
    while(first->link!=NULL){
        del=first->link;
        first->link=del->link;
        delete del;
    }
}
template<class T>
int List<T>::length(){
    linkNode<T>* q;
    int count=0;
    while(q->link!=NULL){
        count++;
        q=q->link;
    }
    return count;
}
template<class T>
linkNode<T>* List<T>::getHead(){
    return first->link;
}
template<class T>
linkNode<T>* List<T>::search(T& x){
    linkNode<T>* current;
    current=first->link;
    while(current->link!=NULL){
        if(current->data==x)
            break;
        current=current->link;
    }
    return current;
}
template<class T>
linkNode<T>* List<T>::locate(int i){
    linkNode<T>* current;
    current=first->link;
    for (int j=1;j<i;j++)
    {
        current=current->link;
    }
    return current;
}
template<class T>
bool List<T>::getData(int i,T& x){
    linkNode<T>* a;
    a=locate(i);
    if (a!=NULL)
    {
        x=a->data;
        return true;
    }
    return false;
}
template<class T>
void List<T>::setData(int i,T& x){
    locate(i)->data=x;
}
template<class T>
bool List<T>::insert(int i,T& x){
    linkNode<T>* newNode=new linkNode<T>(x);
    if(newNode==NULL)
        cerr<<"error"<<endl;
    linkNode<T>* current;
    current=locate(i);
    if(current==NULL)
        return false;
    else{
        newNode->link=current->link;
        current->link=newNode;
    }
    return true;
}
template<class T>
bool List<T>::remove(int i,T& x){
    linkNode<T>* current;
    linkNode<T>* del;
    current=locate(i-1);
    if(current==NULL)
        return false;
    del=current->link;
    x=del->data;
    current=del->link;
    delete del;
    return true;
}
template<class T>
bool List<T>::isEmpty(){
    if(first->link==NULL)
        return true;
    else
        return false;
}
void main(){
    List<int> ls;
    int t,k;
    ls.insert(1,t);
    ls.getData(1,k);
    cout<<k<<endl;
    
}