Thread: Object's array on the stack vs array on the heap

  1. #1
    Registered User
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    Object's array on the stack vs array on the heap

    Is there any benefit to having this:

    OPTION 1:
    Code:
    class stackArray{    
    static const int STACK_SIZE = 3;
    public:
        stackArray(){
            item = new int[STACK_SIZE];
            item[0] = 100;
            item[1] = 101;
            item[2] = 102;
        };
        int *item;
    };
    over this:

    OPTION 2:
    Code:
    class stackArray{    
    static const int STACK_SIZE = 3;
    public:
        stackArray(){
            item[0] = 100;
            item[1] = 101;
            item[2] = 102;
        };
        int item[STACK_SIZE];
    };

    I would think that option 2 could cause dangling pointers but when I test it, it isn't the case. I tested option 2 with the following code:

    Code:
    stackArray createObject(){    
    stackArray instance1;
        return instance1;
    }
    
    
    int main (){
        cout << createObject().item[0] << endl;
        cout << createObject().item[1] << endl;
        cout << createObject().item[2] << endl;
        return 0;
    }
    And it printed out the array the same as option 1 with no garbage values.
    Last edited by Vespasian_2; 03-18-2019 at 01:02 AM.

  2. #2
    C++ Witch laserlight's Avatar
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    Your option 1 is problematic because you didn't also define the destructor to delete[], and then you didn't define or disable copying. But if you had done these, it would be okay, just that it would have been better to have a std::vector<int> member instead.

    Your option 2 is fine: there are no pointers involved (other than by conversion) so I don't see why you would worry about dangling pointers.

    The advantage of option 1 is of course that it has a dynamic array so the array could be resized at some point, but since STACK_SIZE is a constant that turns out to be not an advantage in this case.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
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  3. #3
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    Thumbs up

    Quote Originally Posted by laserlight View Post
    Your option 1 is problematic because you didn't also define the destructor to delete[], and then you didn't define or disable copying. But if you had done these, it would be okay, just that it would have been better to have a std::vector<int> member instead.

    Your option 2 is fine: there are no pointers involved (other than by conversion) so I don't see why you would worry about dangling pointers.

    The advantage of option 1 is of course that it has a dynamic array so the array could be resized at some point, but since STACK_SIZE is a constant that turns out to be not an advantage in this case.
    Got it. Thanks again Laserlight, quality response as always.

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