方法调用上的C 细分故障

我正在努力进行分配，其中我必须为C 中的给定链接列表创建一个深层复制构造函数。在复制构造函数内部，代码和指针正常工作，但是当打印功能被称为时，我会在第59行的函数中获得分段故障：

cout << v->elem << " ";

我一直在尝试进行数小时的调试，我不知道为什么会发生SEG故障。分配的代码（仅复制构造函数是我的代码）：

#include <iostream>
#include <stddef.h>
#include "intSLinkedList.h"
using namespace std;
intSLinkedList::intSLinkedList(const intSLinkedList& other){
    if(other.head == NULL){
        this->head = NULL;
    }
    else{
        intSNode* src_cursor = other.head;
        while(src_cursor != NULL){
            this->addFront(src_cursor->elem);
            src_cursor = src_cursor->next;  
        }
    }
}
intSLinkedList::intSLinkedList(): head(NULL), tail(NULL) { }
bool intSLinkedList::empty() const{ return head == NULL; }
const int& intSLinkedList::front() const{ return head->elem; }
//intSLinkedList::~intSLinkedList(){ while (!empty()) removeFront(); }
void intSLinkedList::addFront(const int& e) {// add to front of list
    intSNode* v = new intSNode;          // create new node
    v->elem = e;                         // store data
        v->next = head;                      // head now follows v
        head = v;                            // v is now the head
    if (head->next==NULL)
        tail = head;
}
void intSLinkedList::addBack(const int& e) {// add to front of list
        intSNode* v = new intSNode;          // create new node
        v->elem = e;
    v->next = NULL;                         // store data
    tail->next = v;                      // head now follows v
    tail = v;
}
void intSLinkedList::removeFront() {         // remove front item
        intSNode* old = head;                // save current head
        head = old->next;                    // skip over old head
        delete old;                          // delete the old head
}
void intSLinkedList::print() {
        intSNode* v = head;
        while (v != NULL){
            cout << v->elem << " ";
            v = v->next;
    }
    cout << endl;
}
int intSLinkedList::count() {
        intSNode* v = head;
    int n = 0;
        while (v != NULL){
        n++;
                v = v->next;
        }
    return n;
}

标题文件：

class intSLinkedList;
class intSNode { 
private: 
    int elem; 
    intSNode* next;     
    friend class intSLinkedList; 
};
class intSLinkedList { 
public: 
    intSLinkedList();
    intSLinkedList(const intSLinkedList& other);
    bool empty() const;
    const int& front() const;
    //~intSLinkedList();
    void addFront(const int& e);
    void addBack(const int& e);
    void removeFront();
    void print();
    int count();
private: 
    intSNode* head; 
    intSNode* tail;
};

和测试器文件：

#include <iostream>
#include "intSLinkedList.h"
using namespace std;
int main(){
    intSLinkedList int_sll;
    int_sll.addFront(5);
    int_sll.addFront(12);
    int_sll.addFront(6);
    cout << "int_sll : ";
    int_sll.print();
    intSLinkedList int_sll2 = int_sll;
    cout << "int_sll2 : ";
        int_sll2.print();
    int_sll.addBack(100);
    cout << "int_sll : ";
    int_sll.print();
    cout << "int_sll2 : ";
        int_sll2.print();
}

我的GDB输出：

int_sll : 6 12 5 
Program received signal SIGSEGV, Segmentation fault.
0x0000000000400cce in intSLinkedList::print (this=0x7fffffffe010)
    at intSLinkedList.cpp:57
57              cout << v->elem << " ";

对正确方向的任何帮助或点都非常感谢。