[英]Constructor and Destructor Declaration Syntax with Template Class
我正在嘗試建立一個實現鏈表的隊列,但遇到編譯器錯誤。 錯誤來自我調用析構函數的行上的重載賦值運算符函數(標有全大寫注釋)。 我有一個預感,這是一個簡單的修復,與我的構造函數/析構函數聲明的語法有關。
我得到的錯誤指出以下代碼: error C2512: 'Queue<char>::Queue' : no appropriate default constructor available
它沒有提到構造函數,但是它所指的那一行是下面我試圖調用析構函數的那一行。
在此先感謝您的幫助。
#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
看看這個線程: 我可以從其類方法中調用析構函數嗎? 。 解決此問題的一種簡單方法是使函數清空隊列,然后從析構函數和賦值運算符調用它。
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();
}
這與模板無關。
如果為類聲明任何構造函數,則將刪除編譯器綜合的默認構造函數(即不帶arg的默認構造函數)。
您必須自己定義Queue()
。
順便說一句,在全局范圍內使用using指令不是一個好主意。
我猜你定義了沒有參數的隊列,例如
Queue<char> quCh;
如果要執行此操作,則必須定義不帶參數的構造函數。
Queue();
或者您必須像這樣定義隊列:
Queue<char> quCh('a');
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