How to return a dynamic object from operator function?

Question

I am writing a operator function for - where my class object is a dynamic array of integer. the operator takes lhs and rhs object and return an object which is the set of elements in lhs but not in rhs.

though I have written the function but I am not able to return the set since the destructor is called right after the object is returned.

IntegerSet & IntegerSet::operator - (IntegerSet & rhs) const
{
    IntegerSet temp(capacity);//local object created to store the elements same size as lhs

    int k=0;
    int lhssize = ElementSize();//no. of elements in the set
    int rhssize = rhs.ElementSize();

    for (int i=0;i<lhssize;i++)
    {
        for (int j=0;j<rhssize;j++)
        {
            if (rhs.ptr[j]!=ptr[i])
            {
                k++;
            }
        }

        if(k==rhssize)
        {
            temp = temp + ptr[i];
        }
        k=0;
    }
    return temp;
}

and here is the constructor if you cannot understand the object

IntegerSet::IntegerSet(const int & size)//works correctly
{
    capacity = size;
    ptr = new int [capacity]();
}

IntegerSet::IntegerSet(const int & size)//works correctly
{
capacity = size;
ptr = new int [capacity]();

}

IntegerSet::IntegerSet(const IntegerSet & copy) : capacity(copy.capacity)//works correctly
{

ptr = copy.clonemaker();
}

IntegerSet::~IntegerSet()
{
capacity = 0;
delete [] ptr;
}


int * IntegerSet::clonemaker() const // works correctly
{
if(ptr==NULL)
{
    return NULL;
}

int *tempptr = new int [capacity];
for(int i=0;i<capacity;i++)
{
    tempptr[i]=ptr[i];
}

return tempptr;

}

Binary arithmetic operators should return values, not references. — juanchopanza, Apr 21 '14 at 12:01
Don't return it by reference, ie, `IntegerSet & IntegerSet::operator-` should be `IntegerSet IntegerSet::operator-` — SirGuy, Apr 21 '14 at 12:01
@GuyGreer thanks it worked.. :) I just got introduced to the reference and const return types so still confused. — Astronautilus, Apr 21 '14 at 12:08

score 4 · Answer 1 · edited May 23 '17 at 11:49

4

You'll have to return by value. The local object will be destroyed when the function returns, and there's no way to prevent that.

For that to work, your class will have to correctly follow the Rule of Three to make sure it's correctly copyable. In C++11 or later, you might also consider making it movable, to avoid unnecessary memory allocation and copying (although, in this case, the copy should be elided anyway).

Better still, follow the Rule of Zero and store a vector<int>, which will do all this for you, rather than trying to juggle raw pointers.

edited May 23 '17 at 11:49

Community

1
1

answered Apr 21 '14 at 12:02

Mike Seymour

249,747
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thanks for the suggestion, but since this is a hw for my course, i am only limited to use the arrays and not any other form of data container. – Astronautilus Apr 21 '14 at 12:06
1

@Astronautilus: OK. In that case, have a good look at your destructor, copy constructor and copy-assignment operator to make sure they'll do the right thing when you your class is copied. – Mike Seymour Apr 21 '14 at 12:08
yeah.. btw if you can check my constructor, copy constructor and destructor that would be good. though I had tested them and they are working fine. – Astronautilus Apr 21 '14 at 12:14

user2672165 · Accepted Answer · 2014-04-21T12:25:33.057

0

You need to change to return the result by value.

IntegerSet IntegerSet::operator - (IntegerSet & rhs) const

Also it would make more sense to supply rhs by const reference when taking a second look.

edited Apr 21 '14 at 12:25

answered Apr 21 '14 at 12:01

user2672165

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How to return a dynamic object from operator function?

2 Answers2