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Thread: explain the copy constructor, shallow copy, and deep copy with examples and c++ code

  1. #1
    Senior Member saneha's Avatar
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    Apr 2011
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    18 explain the copy constructor, shallow copy, and deep copy with examples and c++ code

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  2. #2
    Administrator Vuhelper's Avatar
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    A copy constructor is used to initialize a newly declared Object from an existing Object. This makes a deep copy like assignment.
    A shallow copy of an object copies all of the member field values. This works well if the fields are values, but may not be what you want for fields that point to dynamically allocated memory. The pointer will be copied. but the memory it points to will not be copied -- the field in both the original object and the copy will then point to the same dynamically allocated memory.

    A deep copy copies all fields, and makes copies of dynamically allocated memory pointed to by the fields. To make a deep copy, you must write a copy constructor and overload the assignment operator, otherwise the copy will point to the original, with disastrous consequences.


    I am giving you one example which perform deep copy in this example if you do not override copy constructor then it will give run time error, not perform as what we want so it will be help full for understanding why we have tooverride copy constructor if compiler provide it by default.

    class base
    {
    int *a;
    public:
    base()
    {}
    void allocate()
    {
    a = new int(10);
    }
    void disp()
    {
    cout<<*a<<endl;
    }
    base(base &b)
    {
    a = new int(*(b.a));
    }
    ~base()
    {
    delete a;
    }
    };

    int _tmain(int argc, _TCHAR* argv[])
    {
    base *b1 = new base;
    b1->allocate();
    base *b2 = new base(*b1);
    b1->disp();
    delete b1;
    b2->disp();
    delete b2;
    return 0;
    }

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