C++自定义队列入队成功但print打印无内容问题排查

我正在尝试向队列中入队数据。
入队操作看似执行成功：当前Node节点的Thing指针不为空，其存储的Thing对象id为预期值7。但ThingQueue的print函数存在异常，相同位置的节点被识别为nullptr，尽管入队和打印函数遍历队列的逻辑完全一致，仍出现该差异。

最小可复现代码 #

#include <iostream>

using namespace std;

struct Thing
{
    int id;
    
    Thing()
    {
        id = 7;
    }
    
    void print()
    {
        cout << "Thing " << to_string(id) << " ";
    }
    
};

class ThingQueue
{
    
public:
    
    ThingQueue()
    {
        front = nullptr;
    }
    
    void enqueue(const Thing &thing)
    {
        cout << "Attempting to enqueue..." << endl;
        Node *curr = front;
        while (curr != nullptr) curr = curr->next;
        curr = new Node;
        curr->next = nullptr;
        curr->thing = (Thing*) &thing;
        cout << "Is curr->thing nullptr? 1 for true, 0 for false: ";
        cout << to_string(curr->thing == nullptr) << endl;
        cout << "curr->thing->id = " << to_string(curr->thing->id) << endl;
    }
    
    void print()
    {
        cout << "Attempting to print..." << endl;
        Node *curr = front;
        cout << "Is curr nullptr? 1 for true, 0 for false: ";
        cout << to_string(curr == nullptr) << endl;
        while (curr != nullptr) {
            curr->thing->print();
            curr = curr->next;
        }

    }

private:
    
    struct Node
    {
        Node *next;
        Thing *thing;
    };
    
    Node *front;

};

int main() {
    Thing *pThing = new Thing();
    ThingQueue *pThingQueue = new ThingQueue();
    pThingQueue->enqueue(*pThing);
    pThingQueue->print();
    std::cout << std::endl;

    return 0;
}

运行输出 #

Attempting to enqueue...
Is curr->thing nullptr? 1 for true, 0 for false: 0
curr->thing->id = 7
Attempting to print...
Is curr nullptr? 1 for true, 0 for false: 1

代码存在两处核心错误：

• 新节点未接入队列链表：enqueue函数中遍历到链表尾部（curr为nullptr）后，直接给局部变量curr分配新节点内存，该操作仅修改了局部指针的指向，既没有更新队列的front指针，也没有将新节点挂载到原有尾节点的next指针上。函数退出后局部变量curr销毁，新节点成为无法访问的泄漏内存，队列的front指针始终保持初始值nullptr，因此打印时直接判定队列为空。
• 存在悬空指针风险：原代码直接存储传入引用参数的地址，若传入的是临时对象，函数退出后对象销毁，存储的指针会成为野指针，引发未定义行为。

修复点包含补全链表挂载逻辑、将Node内的Thing成员改为值类型直接拷贝存储对象，示例暂未处理内存释放逻辑：

#include <iostream>

using namespace std;

struct Thing
{
    int id;
    
    Thing()
    {
        id = 7;
    }
    
    void print()
    {
        cout << "Thing " << to_string(id) << " ";
    }
    
};

class ThingQueue
{
    
public:
    
    ThingQueue()
    {
        front = nullptr;
    }
    
    void enqueue(const Thing &thing)
    {
        if (front == nullptr)
        {
             // 队列为空，直接给front分配新节点
             front = new Node;
             front->next = nullptr;
             front->thing = thing;
        }
        else
        {
             // 队列非空，遍历找到尾节点
             Node* curr = front;
             while (curr->next != nullptr)
                  curr = curr->next;
             // 将新节点挂载到尾节点的next指针上
             curr->next = new Node;
             curr->next->next = nullptr;
             curr->next->thing = thing;
        }
    }

    
    void print()
    {
        Node *curr = front;
        while (curr != nullptr) {
            curr->thing.print();
            curr = curr->next;
        }

    }

private:
    
    struct Node
    {
        Node *next;
        Thing thing;
    };
    
    Node *front;

};

class Stuff
{
    
};

int main() {
    Thing thing = Thing();
    Thing thing2 = Thing();
    Thing thing3 = Thing();
    ThingQueue tq = ThingQueue();
    tq.enqueue(thing);
    tq.enqueue(thing2);
    tq.enqueue(thing3);
    tq.print();
    return 0;
}

内容的提问来源于stack exchange，提问作者K Man