Question

我正在尝试创建一个实现链表的队列，但遇到了编译错误。错误来自我调用析构函数的行上的重载赋值运算符函数（标有全部大括号注释）。我有预感这是一个简单的修复，它与我的构造函数/析构函数声明的语法有关。

我收到的错误说明了以下代码：error C2512: 'Queue<char>::Queue' : no appropriate default constructor available

它没有提到构造函数，但它引用的行是我试图调用析构函数的行。

提前感谢您的帮助。

#ifndef QUEUE_H
#define QUEUE_H
#include <iostream>
using namespace std;

template <class Type>
class Queue     // Create a Queue data structure implementing a linked list
{
    private:        // The private members
        struct Cell     // The Cell class will be the blueprints for each link in the list
        {
            Type data;      // The information held by the cell
            Cell* next;     // The link to the next cell
        };

        Cell* first = NULL;
        Cell* last = NULL;


    public:     // The public members
        Queue(Type);
        bool isEmpty();
        void push(Type);
        Type pop();
        Queue<Type>& operator=(Queue<Type>&);
        friend ostream& operator<<(ostream&, const Queue<Type>&);
        ~Queue();
};


template<class Type>
Queue<Type>::Queue(Type inputData)      // Constructor that initializes the queue with a new cell that last and first point to
{
    first = new Cell;

    first->data = inputData;
    first->next = NULL;

    last = first;
}




template<class Type>
Queue<Type>& Queue<Type>::operator=(Queue<Type>& queue)     // Overload "=" so that it performs a deep copy of a Queue object
{
    if (!queue.isEmpty())
    {
        ~Queue();      // HERE IS THE ERROR LINE

        Cell* rhs = queue.first;

        while (rhs != NULL)
        {
            push(rhs->data);
            rhs = rhs->next;
        }
    }

    return *this;
}




template<class Type>
Queue<Type>::~Queue()       // Destructor that deallocates all of the memory used by the queue.
{
    if (!isEmpty())     // We only need to deallocate the queue if it is non-empty
    {
        Cell *link = last;

        while (link != NULL)        // Until we reach the end of the queue, keep deleting each link
        {
            pop();
        }

        first = NULL;
        last = NULL;
    }
    else        // If the queue is already empty, let the user know
    {
        cout << "Cannot call destructor. The list is already empty.\n";
    }
}
#endif

Answer 1

查看此主题：Can i call destructor from its class method?。一个简单的方法是创建一个清空队列的函数，然后从析构函数和赋值运算符中调用它。

template<class Type>
void Queue<Type> empty(){
    if (!isEmpty())     // We only need to deallocate the queue if it is non-empty
    {
         Cell *link = last;

        while (link != NULL)        // Until we reach the end of the queue, keep deleting each link
        {
            pop();
        }

        first = NULL;
        last = NULL;
    }
    else        // If the queue is already empty, let the user know
    {
        cout << "Cannot call empty. The list is already empty.\n";
    }
}

template<class Type>
Queue<Type>& Queue<Type>::operator=(Queue<Type>& queue)     // Overload "=" so that it performs a deep copy of a Queue object
{
    if (!queue.isEmpty())
    {
        empty();      // Tada, no more error

        Cell* rhs = queue.first;

        while (rhs != NULL)
        {
            push(rhs->data);
            rhs = rhs->next;
        }
    }

    return *this;
}




template<class Type>
Queue<Type>::~Queue()       // Deconstructor that deallocates all of the memory used by the queue.
{
    empty();
}

Answer 2

这与模板无关。

如果为类声明任何构造函数，则编译器合成的默认构造函数（即不带arg的构造函数）将被删除。

您必须自己定义Queue()。

BTW，全局范围内的using指令不是一个好主意。

Answer 3

我猜你定义了一个没有参数的队列，比如

Queue<char> quCh;

如果要执行此操作，则必须定义不带参数的构造函数。

Queue();

或者你必须像这样定义你的队列：

Queue<char> quCh('a');

使用模板类的构造函数和析构函数声明语法

3 个答案: