Choose at runtime array or vector in C++

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?

You know that `vector` can return a pointer that is binary compatible with `T*`, right? — StoryTeller - Unslander Monica, May 06 '16 at 14:16
You got your answer, but I still really want to know... why do both? — StoryTeller - Unslander Monica, May 06 '16 at 14:23
I do understand, im putting a point here if i can or not. This is not part of my code which i am using. This is just an example to what i am looking for. — , May 06 '16 at 14:36

score 3 · Answer 1 · answered May 06 '16 at 14:14

3

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.

answered May 06 '16 at 14:14

Lightness Races in Orbit

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+1 for "using only the vector version" No sense of keeping that dangerous int* around when you have access to the stl. – DeathTails May 06 '16 at 14:23
I accept your solution, but my point is to find out a way to what the object has been initialized with. This is just an example to put my point. – May 06 '16 at 14:32
Logically im expecting there should be more powers to an object to understand its state or how its been initialized. Looks like it has very little practical application in C++. Anyways thank you dear. – May 06 '16 at 14:52
@raghureddy: What constitutes the state of an object is determined by the person who writes the class. That's you. You can accomplish it in the manner I explained in my answer. – Lightness Races in Orbit May 06 '16 at 15:21

score 1 · Answer 2 · edited May 23 '17 at 12:31

1

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.

edited May 23 '17 at 12:31

Community

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answered May 06 '16 at 14:15

Giorgi Moniava

27,046
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Or set the size to a negative value in one case, and save the space of another member... – StoryTeller - Unslander Monica May 06 '16 at 14:17
@LightnessRacesinOrbit, it's not stealing if I share it willingly :) – StoryTeller - Unslander Monica May 06 '16 at 14:18
1

@StoryTeller: It is when I don't give you any attribution :) – Lightness Races in Orbit May 06 '16 at 14:19

Choose at runtime array or vector in C++

2 Answers2