Dynamic Array deleting old pointer and setting it to new array C++

Question

I am trying to implement an insert() function that should insert a value into a boolean array and set the index equal to that value to 'true'. The IntSet object has a pointer, value, to an array of booleans and an int, size, to hold the size of the array. So IntSet A(2, 4, 10); will create an array of size 10 and the indexes at 2, 4, 10 will be set to true.

The insert() function returns true or false depending on if it inserted the value or not, and it should resize the array if the inserted value is larger than the size of the array. So, A.insert(1000); would resize the array to size 1001 and set the value at index 1000 to true.

My issue is with deleting the old array pointer and setting it to the new, resized array. No matter what I do, it always breaks at the delete[], and I'm not sure why.

This is what I have so far:

bool IntSet::insert(int toInsert) {

int tempSize = this->size;

// if toInsert is greater than the number of elements in the array, call 
// copy constructor and assign new value to true
if(toInsert < this->size && toInsert >= 0) {

    value[toInsert] = true;
    return true;
}
IntSet largerSet(toInsert+1);
if(toInsert > this->size+1) {


    for(int i = 0; i < largerSet.size+1; i++) {

        largerSet.value[i] = false;
    }

    largerSet.value[toInsert] = true;

    for(int i = 0; i < tempSize+1; i++) {

        if(this->value[i] != false) {
            largerSet.value[i] = true;
        }
    }

    std::swap(value, largerSet.value);
    std::swap(size, largerSet.size);
}

return true;
}

EDIT: used swap to move value to current array.

I hope I was clear enough in my explanation, if you need more clarification I'm happy to provide more code. This is for a class assignment, so I'm not expecting a direct answer, but anything that can point me to the right direction will help immensely.

Thanks all!

iavr · Accepted Answer · 2013-10-17 00:53:41Z

1

You should leave allocations to constructors, deallocations to destructors, copies to copy constructors and copy assignment operators. You now have a function that does a little bit of everything.

A clean way to reallocate is first to provide a swap function (that swaps your pointer + size); given that, create a temporary of the new size (like largerSet), initialize the new data, then swap your set with largerSet. As the temporary goes out of scope, it gets destroyed, and delete[] is called automatically.

Now when largerSet goes out of scope, largerSet.value gets deleted (I assume this is done in your destructor), but this now equals value, so your data are gone.

edited Oct 17, 2013 at 0:53

answered Oct 17, 2013 at 0:46

iavr

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4 Comments

floatfil Over a year ago

Thanks a lot for the info. The problem is I can't add any more functions and we're told to have the resize and reallocation done within insert(). The issue is that it's not even calling delete[] and just breaks when it tries :/

iavr Over a year ago

Ok then provide the swap operation inline: std::swap(value,largerSet.value); std::swap(size,largerSet.size);. Remove tempSet and newSet. Remove delete[], leave one only in the destructor. There is a destructor, isn't there?

floatfil Over a year ago

Thanks, that definitely solved the problem of moving the values to the new array. But once the function goes out of scope and calls the destructor to delete largerSet, it breaks. I have no delete[] in the insert function anymore and I removed tempSet and newSet. This is my destructor: delete[] (this->value); this->value = NULL;

iavr Over a year ago

Sounds ok. I can still see other problems that may or may not cause the program to break (if conditions, sizes in for loops...). But I would tend to re-write than correct, and I'd need the entire code. In short, toInsert should be unsigned; the 2nd if should not be there; initialization to false is useless and all copying should be part of a constructor, if that's permitted.

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