Question

I am working on a project that requires a class QueueArray that is an Array of Queues. It’s been a while since I worked with c++ Arrays so I’m having some trouble debugging why my code is throwing errors.

I read Delete an array of queue objects for some inspiration (along with a couple hours on Google), but I am still having errors with the following code:

    #include <iostream>
    #include <deque>
    #include <queue>
    using namespace std;

    class QueueArray
    {

        queue<int> theArray[];

        QueueArray::QueueArray(int size)
        {
            queue<int> theArray[] = new queue<int>[size];
            //theArray[] = new queue<int>[size]; //this may be closer, but also giving errors

        }
    };

the errors are:

warning C4200: nonstandard extension used : zero-sized array in struct/union
1> Cannot generate copy-ctor or copy-assignment operator when UDT contains a zero-sized array

and

error C2075: ‘theArray’ : array initialization needs curly braces

I’ve read up about the 2nd error, but I can seem to figure out what I need to do to fix it.

I need it to be a variable sized array, with the variable passed to the class, which is why I can not initialize the size of the array up top, and It must be of global scope so I can use it in other functions within the class (the classes can’t be passed the array through a parameter).

Later on, the queues will be of a user defined type, but we’re letting them be queues of ints right now, not sure if that makes a difference. I keep seeing people suggesting the use of vectors in these cases but I don’t have a choice on this one.

Any suggestions would be appreciated.

Answer 1

using variable sized arrays is not possible in C++. to make your code working, use a pointer, i.e.

class QueueArray
{
    queue<int> * const theArray;

    QueueArray::QueueArray(int size)
    : theArray (new queue<int>[size])
    { /* ... */ }
    ~QueueArray()
    { delete[] theArray; }
};

However, in C++ you should really avoid this and use a std::vector instead, i.e.

typedef vector<queue<int>> QueueArray;