在C ++中选择运行时数组或向量

Question

I have a problem described as below ::

    class datad {
    private:
        int *a;
        int _size;
        vector<int> v;

    public:
        datad(int arr[], int size) {
            _size = size;
            for (int i = 0; i < size; i++)
                a[i] = arr[i];
        }
        datad(vector<int> ve)
        {
            v = ve;
            _size = ve.size();
        }

        void printdata()
        {
             // print data which the object has been initialized with
             // if object is initialized with vector then print vector
             // array print array
        }
    };

   int main()
   {
        // print only vector data
    int a[] = { 9,4,8,3,1,6,5 };
    datad d(v1);
    d.printdata();

    // print only array data

    datad d1(a, 7);
    d1.printdata();
 }

I need to find the way the object is initialized and then based on the same should be able to printdata accrodingly. Can someone help me understand if it is possible at all?

Answer 1

Add a bool usesVector to your class and set it to true or false in each constructor as appropriate. Then, in printdata , simply check the value of the boolean.

Or you can set size to -1 in the vector case (as it's otherwise unused) and just check for that.

By the way, your array implementation is broken, because you never allocate any memory for it. You'd be much better off using only the vector version. You can still initialise that vector from array data if you wish.

Answer 2

You can set a flag in respective constructor and check that flag during the printing method.

I hope this is for learning purposes, otherwise as noted you maybe better of using just the vector version. When using dynamic memory management in class you need to be aware of things like rule of three and I guess there is also rule of five.