编码队列模板类时出现错误C2955

Question

Making a queue class using templates for my data structures class. I'm getting a C2955 "Queue - use of class template requires template argument list" when I build, among a bunch of other errors which I think spawn from this one. I've compared this program to others which used templates and I can't seem to figure out what's different about this. Can anyone help me through it?

//Queue.cpp
#include <iostream>
#include "Queue.h"

using namespace std;

//Default constructor for Queue object
template<class ItemType>
Queue<ItemType>::Queue() {
    front = 0;
    back = 0;
    count = 0;
}

//Check if the queue is empty
template<class ItemType>
bool Queue<ItemType>::empty() const {

    if (count == 0) {
        return true;
    }
    else {
        return false;
    }
}

//Remove the first item in the queue
template<class ItemType>
bool Queue<ItemType>::dequeue() {

    int p = count;

    for (int i = 0; i < count - 1; i++) {
        items[i] = items[i + 1];
    }

    count--;

    if (p > count) {
        return true;
    } else {
        return false
    }

}

//Add an entry to the beginning of the queue
template<class ItemType>
bool Queue<ItemType>::enqueue(const itemType &item) { 

    count++;
    items[count - 1] = item;

    return true;
}

template<class ItemType>
bool Queue<ItemType>::peekFront(itemType &item) const {
    item = items[0];
    return true;
}

template<class ItemType>
int Queue<ItemType>::getSize() const {
    return count;
}  

There are no apparent syntax errors in Queue.cpp that I can find. I know that back and front aren't used but I'm not sure what they're meant for yet. Our professor provided us with most of the header file, and the main.

//Queue.h
#ifndef _QUEUE
#define _QUEUE
#include<iostream>
#include<vector>
using namespace std;
const int MAX_SIZE=10;
typedef int itemType;

template <class ItemType>
class Queue {
public:
    Queue();  // Constructor. Initialize front=0, back=0, count=0 
    bool empty() const; // To test if the queue is empty. Return true if it          is, flase if it is not. 
    bool dequeue(); // Remove the front entry from the queue
    bool enqueue(const itemType &item); // Add new entry called item at the     back of the queue. 
    bool peekFront(itemType &item) const; // Retrieve the front entry from the queue
    int getSize() const ;  // To get the number of the entries in the queue


    vector<itemType> toVector() const  // to convert the queue to a vector
    {
        vector<itemType> vectorQ;

        int i=front;
        int size=count;
        while (size>0)
        {
            i=i%MAX_SIZE;
            vectorQ.push_back(items[i]);
            i++;
            size--;
        }
        return vectorQ;

    }

private:
    int front, back; 
    int count;
    itemType items[MAX_SIZE];  // items is a circular array to store the queue.

};

#endif

In the main, when "Queue q;" is called to make an empty queue object, there is a red line saying "argument list for class template "Queue" is missing

#include "Queue.h"
#include "Queue.cpp"

using namespace std;

void displayQ(Queue & queue)
{
    cout << "The queue contains :\n" ;
    vector<int> queueItems=queue.toVector();
    for (int i=0; i<queue.getSize(); i++)
    {
        cout <<queueItems[i] << " ";
    }
    cout << endl;
}    

int main()
{
    Queue q;  //create an empty queue

    bool flag=q.empty(); // To test if the queue is really empty.
    if (flag)  
        cout <<"The queue is empty.\n";

    q.enqueue(1);  //To test the enqueue function by inserting a set of numbers (1-10) into q. 
    q.enqueue(2);
    q.enqueue(3);
    q.enqueue(4);
    q.enqueue(5);
    q.enqueue(6);
    q.enqueue(7);
    q.enqueue(8);
    q.enqueue(9);
    q.enqueue(10);
    displayQ(q);  // Display the contents in q.

    int buffer;   // To test the peekFront function. The buffer should hold the the value of the front entry  
    q.peekFront(buffer);
    cout << "The front entry of the queue is " << buffer << " .\n";

    flag=q.enqueue(11); // To test the returned value of the enqueue fnction. It returns flase when the q has no room 
    if (!flag)
        cout << "The queue is full. No room for insertion.\n";

    q.dequeue(); // To test the dequeue function. Remove the first two entries from the q.
    q.dequeue();
    displayQ(q);  // Display the contents in q.

    q.enqueue(11);  // Does the q have room to hold two more new entry?
    q.enqueue(12);
    displayQ(q);  // Display the contents in q.

    q.peekFront(buffer); // what's the front entry of the q now?  
    cout << "The front entry of the queue is " << buffer << " .\n";

}

Other errors I get when building are C2662 and C2244

Answer 1

As the error message says, you have to add template argumet list to use Queue .

Change

void displayQ(Queue & queue)

to

template<class itemType>
void displayQ(Queue<itemType> & queue)

Then, change

Queue q;  //create an empty queue

in main() to

Queue<int> q;  //create an empty queue

Finally, change

return false

in bool Queue<ItemType>::dequeue() to

return false;

(add a semicolon)

Also you should remove #include "Queue.cpp" and move the implementations of member functions in Queue.cpp to Queue.h because including .cpp is generally considered as bad because it may lead to linker error for duplicate definition, and temlate functions cannot be used if they are in different translation unit.

One more point: The comment says that

flag=q.enqueue(11); // To test the returned value of the enqueue fnction. It returns flase when the q has no room

but actual implementation

//Add an entry to the beginning of the queue
template<class ItemType>
bool Queue<ItemType>::enqueue(const itemType &item) { 

    count++;
    items[count - 1] = item;

    return true;
}

doesn't do what is said in the comment and cause out-of-range access. You should do one of these:

• Inclease MAX_SIZE to a value that is large enough.
• Implement error checking.