Why am I getting "is private" errors when using class members to access another class's private members?

Question

I'm instantiating a QueueDeque or a StackDeque based on user choice and storing widgets in them. I don't know why I'm getting 'is private' errors every time my StackDeque/QueueDeque calls a member function. Does it have something to do with how I'm instantiating them? I haven't learned handlers yet.

DequeArray.h:

#if !defined NULL
#define NULL 0
#endif

#if !defined (DEQUEARRAY_H)
#define DEQUEARRAY_H
#include <iostream>

template < class T >
class DequeArray
{
    private:
        int max_queue;
        T** items;
        int front;
        int back;
        int sz;

        void arrayResize(int new_size);

    public:
        DequeArray();
        ~DequeArray();

        bool isEmpty();
        int size();
        void dequeueAll();

        T* peek();
        T* peekDeque();

        void enqueue(T* item);
        void enqueueDeque(T* item);

        T* dequeue();
        T* dequeueDeque();
};

template < class T >
DequeArray<T>::DequeArray()
{
    max_queue = 2;
    items = new T*[max_queue];
    front = 0;
    back = max_queue - 1;
    sz = 0;
}

template < class T >
DequeArray<T>::~DequeArray()
{
    delete[] items;
}

template < class T >
bool DequeArray<T>::isEmpty()
{
    return sz == 0;
}

template < class T >
int DequeArray<T>::size()
{
    return sz;
}

template < class T >
void DequeArray<T>::dequeueAll()
{
    delete[] items;

    max_queue = 2;
    items = new T*[max_queue];  
    front = 0;
    back = max_queue - 1;
    sz = 0;
}

template < class T >
T* DequeArray<T>::peek()
{
    T* item = NULL;
    if (!isEmpty()) 
    {  
        item = items[front];
    }
    return item;
}

template < class T >
void DequeArray<T>::enqueue(T* item)
{
   if (sz == max_queue)
   {
      arrayResize(2*max_queue);
   }

   //back = (back + 1) % (max_queue);
   back = back + 1;
   if (back == max_queue) back = 0;
   items[back] = item;
   sz++;
}

template < class T >
T* DequeArray<T>::dequeue()
{
    T* item = NULL;

    if (!isEmpty()) 
    {
        item = items[front];
        items[front] = NULL;
        //front = (front + 1) % (max_queue);
        front = front + 1;
        if (front == max_queue) front = 0;
        sz--;
   }
   return item;
}

template < class T >
T* DequeArray<T>::peekDeque()
{
    T* item = NULL;
    if (!isEmpty())
    {
        item = items[back];
    }
    return item;
}

template < class T >
void DequeArray<T>::enqueueDeque(T* item)
{
    if (sz == max_queue)
        arrayResize(2*max_queue);

    front = front - 1;
    if (front == max_queue)
        front = 0;
    items[front] = item;
    sz++;
}

template < class T >
T* DequeArray<T>::dequeueDeque()
{
    T* item = NULL;

    if (!isEmpty())
    {
        item = items[back];
        items[back] = NULL;
        back = back - 1;
        if (back == front)
            back = 0;
        sz--;
    }
}

template < class T >
void DequeArray<T>::arrayResize(int new_size)
{
   T** temp = new T*[new_size];
   int j = front;

   for (int i = 0; i < sz; i++)
   {
      temp[i] = items[j];
      j++;
      if (j == max_queue) j = 0;
   }

   front = 0;
   back = sz - 1;
   max_queue = new_size;

   delete[] items;
   items = temp;
}
#endif

StackDeque.h:

#if !defined NULL
#define NULL 0
#endif

#if !defined (STACKDEQUE_H)
#define STACKDEQUE_H
#include "DequeArray.h"
using CSC2110::DequeArray;
#include "Widget.h"

template < class T >
class StackDeque
{
    private:
        DequeArray<T>* da;

    public:
        StackDeque();
        ~StackDeque();
        void push(T* item);
        T* pop();
        T* peek();
        int sz;
        bool isEmpty();
};

template < class T >
StackDeque<T>::StackDeque()
{
    da = new DequeArray<T>;
}

template < class T >
StackDeque<T>::~StackDeque()
{
    da->dequeueAll();
}

template < class T >
void StackDeque<T>::push(T* item)
{
    da->enqueueDeque(item);
}

template < class T >
T* StackDeque<T>::pop()
{
    T* temp = NULL;
    if (!da->isEmpty())
    {
        temp->da->enqueueDeque();
        return temp;
    }
}

template < class T >
bool StackDeque<T>::isEmpty()
{
    return sz == 0;
}
#endif

InventoryManager.cpp:

#include "Widget.h"
#include "StackDeque.h"
#include "QueueDeque.h"
#include "DequeArray.h"
#include "InventoryManager.h"

namespace CSC2110
{

InventoryManager::InventoryManager(int inventory_choice)
{
    totalProf = 0;
    choice = inventory_choice;
    if (inventory_choice == 1)
    {
        stack = new StackDeque<Widget>;
    }
    else
    {
        queue = new QueueDeque<Widget>;
    }
}

InventoryManager::~InventoryManager()
{

}

void InventoryManager::buyWidgets(double cost, int num_to_buy)
{
    if (choice == 1)
    {
        for (int i = 0; i < num_to_buy; i++)
        {
            Widget* widget = new Widget(cost);
            stack->push(widget);
            delete widget;
        }
    }
    else
    {
        for (int i = 0; i < num_to_buy; i++)
        {
            Widget* widget = new Widget(cost);
            queue->enqueue(widget);
            delete widget;
        }
    }
}

double InventoryManager::getTotalProfit()
{
    return totalProf;
}

double InventoryManager::sellWidgets(double price, int num_to_sell)
{
    double profitThisTransaction = 0;
    double profitPerSell = 0;

    if (choice == 1)
    {
        if (num_to_sell > stack->sz)
        num_to_sell = stack->sz;

        for (int i= 0; i < num_to_sell; i++)
        {
            Widget* widget = NULL;
            widget = stack->pop();

            profitPerSell = price - widget->getCost();
            profitThisTransaction += profitPerSell;
            delete widget;
        }
    }

    else
    {
        if (num_to_sell > queue->sz)
            num_to_sell = queue->sz;

        for (int i= 0; i < num_to_sell; i++)
        {
            Widget* widget = NULL;
            widget = queue->dequeue();

            profitPerSell = price - widget->getCost();
            profitThisTransaction += profitPerSell;
            delete widget;
        }
    }

totalProf += profitThisTransaction;
return profitThisTransaction;

}
}

Widget.cpp:

#include "Widget.h"

namespace CSC2110
{

Widget::Widget(double user_choice)
{
    cost = user_choice;
}

Widget::~Widget()
{

}

float Widget::getCost()
{
    return cost;
}

}

Errors:

In file included from StackDeque.h:7:0,
                 from InventoryManager.cpp:2:
QueueDeque.h: In instantiation of 'void CSC2110::QueueDeque<T>::enqueue(T*) [with T = CSC2110::Widget]':
InventoryManager.cpp:42:25:   required from here
DequeArray.h:16:7: error: 'int CSC2110::DequeArray<CSC2110::Widget>::max_queue' is private
   int max_queue;
       ^
In file included from InventoryManager.cpp:3:0:
QueueDeque.h:55:9: error: within this context
  if (sz == da->max_queue)
         ^
In file included from StackDeque.h:7:0,
                 from InventoryManager.cpp:2:
DequeArray.h:16:7: error: 'int CSC2110::DequeArray<CSC2110::Widget>::max_queue' is private
   int max_queue;
       ^
In file included from InventoryManager.cpp:3:0:
QueueDeque.h:57:20: error: within this context
   da->arrayResize(2*da->max_queue);
                    ^
In file included from StackDeque.h:7:0,
                 from InventoryManager.cpp:2:
DequeArray.h:166:6: error: 'void CSC2110::DequeArray<T>::arrayResize(int) [with T = CSC2110::Widget]' is private
 void DequeArray<T>::arrayResize(int new_size)
      ^
In file included from InventoryManager.cpp:3:0:
QueueDeque.h:57:3: error: within this context
   da->arrayResize(2*da->max_queue);
   ^
In file included from StackDeque.h:7:0,
                 from InventoryManager.cpp:2:
DequeArray.h:19:7: error: 'int CSC2110::DequeArray<CSC2110::Widget>::back' is private
   int back;
       ^
In file included from InventoryManager.cpp:3:0:
QueueDeque.h:61:11: error: within this context
  da->back = da->back + 1;
           ^
In file included from StackDeque.h:7:0,
                 from InventoryManager.cpp:2:
DequeArray.h:19:7: error: 'int CSC2110::DequeArray<CSC2110::Widget>::back' is private
   int back;
       ^
In file included from InventoryManager.cpp:3:0:
QueueDeque.h:61:22: error: within this context
  da->back = da->back + 1;
                      ^
In file included from StackDeque.h:7:0,
                 from InventoryManager.cpp:2:
DequeArray.h:19:7: error: 'int CSC2110::DequeArray<CSC2110::Widget>::back' is private
   int back;
       ^
In file included from InventoryManager.cpp:3:0:
QueueDeque.h:62:15: error: within this context
  if (da->back == da->max_queue) da->back = 0;
               ^
In file included from StackDeque.h:7:0,
                 from InventoryManager.cpp:2:
DequeArray.h:16:7: error: 'int CSC2110::DequeArray<CSC2110::Widget>::max_queue' is private
   int max_queue;
       ^
In file included from InventoryManager.cpp:3:0:
QueueDeque.h:62:15: error: within this context
  if (da->back == da->max_queue) da->back = 0;
               ^
In file included from StackDeque.h:7:0,
                 from InventoryManager.cpp:2:
DequeArray.h:19:7: error: 'int CSC2110::DequeArray<CSC2110::Widget>::back' is private
   int back;
       ^
In file included from InventoryManager.cpp:3:0:
QueueDeque.h:62:42: error: within this context
  if (da->back == da->max_queue) da->back = 0;
                                          ^
In file included from StackDeque.h:7:0,
                 from InventoryManager.cpp:2:
DequeArray.h:17:7: error: 'CSC2110::Widget** CSC2110::DequeArray<CSC2110::Widget>::items' is private
   T** items;
       ^
In file included from InventoryManager.cpp:3:0:
QueueDeque.h:63:11: error: within this context
  da->items[da->back] = item;
           ^
In file included from StackDeque.h:7:0,
                 from InventoryManager.cpp:2:
DequeArray.h:19:7: error: 'int CSC2110::DequeArray<CSC2110::Widget>::back' is private
   int back;
       ^
In file included from InventoryManager.cpp:3:0:
QueueDeque.h:63:11: error: within this context
  da->items[da->back] = item;
           ^
In file included from InventoryManager.cpp:2:0:
StackDeque.h: In instantiation of 'T* CSC2110::StackDeque<T>::pop() [with T = CSC2110::Widget]':
InventoryManager.cpp:65:24:   required from here
StackDeque.h:53:3: error: 'class CSC2110::Widget' has no member named 'da'
   temp->da->enqueueDeque();
   ^
In file included from StackDeque.h:7:0,
                 from InventoryManager.cpp:2:
QueueDeque.h: In instantiation of 'T* CSC2110::QueueDeque<T>::dequeue() [with T = CSC2110::Widget]':
InventoryManager.cpp:80:28:   required from here
DequeArray.h:17:7: error: 'CSC2110::Widget** CSC2110::DequeArray<CSC2110::Widget>::items' is private
   T** items;
       ^
In file included from InventoryManager.cpp:3:0:
QueueDeque.h:74:19: error: within this context
   item = da->items[da->front];
                   ^
In file included from StackDeque.h:7:0,
                 from InventoryManager.cpp:2:
DequeArray.h:18:7: error: 'int CSC2110::DequeArray<CSC2110::Widget>::front' is private
   int front;
       ^
In file included from InventoryManager.cpp:3:0:
QueueDeque.h:74:19: error: within this context
   item = da->items[da->front];
                   ^
In file included from StackDeque.h:7:0,
                 from InventoryManager.cpp:2:
DequeArray.h:17:7: error: 'CSC2110::Widget** CSC2110::DequeArray<CSC2110::Widget>::items' is private
   T** items;
       ^
In file included from InventoryManager.cpp:3:0:
QueueDeque.h:75:12: error: within this context
   da->items[da->front] = NULL;
            ^
In file included from StackDeque.h:7:0,
                 from InventoryManager.cpp:2:
DequeArray.h:18:7: error: 'int CSC2110::DequeArray<CSC2110::Widget>::front' is private
   int front;
       ^
In file included from InventoryManager.cpp:3:0:
QueueDeque.h:75:12: error: within this context
   da->items[da->front] = NULL;
            ^
In file included from StackDeque.h:7:0,
                 from InventoryManager.cpp:2:
DequeArray.h:18:7: error: 'int CSC2110::DequeArray<CSC2110::Widget>::front' is private
   int front;
       ^
In file included from InventoryManager.cpp:3:0:
QueueDeque.h:77:13: error: within this context
   da->front = da->front + 1;
             ^
In file included from StackDeque.h:7:0,
                 from InventoryManager.cpp:2:
DequeArray.h:18:7: error: 'int CSC2110::DequeArray<CSC2110::Widget>::front' is private
   int front;
       ^
In file included from InventoryManager.cpp:3:0:
QueueDeque.h:77:25: error: within this context
   da->front = da->front + 1;
                         ^
In file included from StackDeque.h:7:0,
                 from InventoryManager.cpp:2:
DequeArray.h:18:7: error: 'int CSC2110::DequeArray<CSC2110::Widget>::front' is private
   int front;
       ^
In file included from InventoryManager.cpp:3:0:
QueueDeque.h:78:17: error: within this context
   if (da->front == da->max_queue) da->front = 0;
                 ^
In file included from StackDeque.h:7:0,
                 from InventoryManager.cpp:2:
DequeArray.h:16:7: error: 'int CSC2110::DequeArray<CSC2110::Widget>::max_queue' is private
   int max_queue;
       ^
In file included from InventoryManager.cpp:3:0:
QueueDeque.h:78:17: error: within this context
   if (da->front == da->max_queue) da->front = 0;
                 ^
In file included from StackDeque.h:7:0,
                 from InventoryManager.cpp:2:
DequeArray.h:18:7: error: 'int CSC2110::DequeArray<CSC2110::Widget>::front' is private
   int front;
       ^
In file included from InventoryManager.cpp:3:0:
QueueDeque.h:78:45: error: within this context
   if (da->front == da->max_queue) da->front = 0;

Answer 1

一个类对象不能访问另一个类的私有方法，只能访问另一个类的公共方法。

Answer 2

The error is clear. You are trying to access private member variables (max_queue, back, front, etc.. ) and private member function (arrayResize) from your inventoryMnager.cpp ... changing their scope to public should solve your problem.