bad_alloc when creating 20k array

Question

I have to do some kind of project and I'm stuck. I'm getting an bad_alloc error. I checked code a lot of times, tried to google some solutions, but still nothing, that's why I'm writing here.The thing is the program runs normally, but at the task manager he memory usage raises to 2GB(that's the limit as I know) and then it crashes. The program needs to check time of allocating space and copying variables. Here's part of the code:

class Table
{
    int *tablica;
    int size;

public:
Table()
    {
        tablica = NULL;
        size = 0;
    }

~Table()
    {
        delete tablica;
        size = 0;
    }

int *push_back(int val)
    {
        int *temp = new int[size];
        if(size % 10 == 0)
        {
            for(int i = 0; i < size; i++)
                temp[i] = tablica[i];
            tablica = new int[size + 10];
            for(int i = 0; i < size; i++)
                tablica[i] = temp[i];
        }
        tablica[size] = val;
        size++;
        delete []temp;
        return tablica;
    }

void test()
    {
            LONGLONG measure[100][6];
        LARGE_INTEGER performanceCountStart, performanceCountEnd;
        int cpy_tab [20000];

        for(int j = 0; j < 100; j++)
        {   
            for(int i = 0; i < 20000; i++)
                cpy_tab[i] = rand() % 10000 - 10000;

            performanceCountStart = startTimer(); 
            for(int i = 0; i < 500; i++)
                {
                    push_back(cpy_tab[i]);
                }
            performanceCountEnd = endTimer();
    measure[j][0] = performanceCountEnd.QuadPart - performanceCountStart.QuadPart;
            cout<<j<<"."<<measure[j][0]<<endl;

            delete []tablica;
            size = 0;

            performanceCountStart = startTimer(); 
            for(int i = 0; i < 2000; i++)
            {
                push_back(cpy_tab[i]);
            }
            performanceCountEnd = endTimer();
    measure[j][1] = performanceCountEnd.QuadPart - performanceCountStart.QuadPart;
            cout<<j<<"."<<measure[j][1]<<endl;

            delete []tablica;
            size = 0;


            performanceCountStart = startTimer(); 
            for(int i = 0; i < 4000; i++)
            {
                push_back(cpy_tab[i]);
            }
            performanceCountEnd = endTimer();
    measure[j][2] = performanceCountEnd.QuadPart - performanceCountStart.QuadPart;
            cout<<j<<"."<<measure[j][2]<<endl;

            delete []tablica;
            size = 0;


            performanceCountStart = startTimer(); 
            for(int i = 0; i < 8000; i++)
            {
                push_back(cpy_tab[i]);
            }
            performanceCountEnd = endTimer();
    measure[j][3] = performanceCountEnd.QuadPart - performanceCountStart.QuadPart;
            cout<<j<<"."<<measure[j][3]<<endl;

            delete []tablica;
            size = 0;


            performanceCountStart = startTimer(); 
            for(int i = 0; i < 14000; i++)
            {
                push_back(cpy_tab[i]);
            }
            performanceCountEnd = endTimer();
    measure[j][4] = performanceCountEnd.QuadPart - performanceCountStart.QuadPart;
            cout<<j<<"."<<measure[j][4]<<endl;

            delete []tablica;
            size = 0;

            performanceCountStart = startTimer(); 
            for(int i = 0; i < 20000; i++)
            {
                push_back(cpy_tab[i]);
            }
            performanceCountEnd = endTimer();
    measure[j][5] = performanceCountEnd.QuadPart - performanceCountStart.QuadPart;
            cout<<j<<"."<<measure[j][5]<<endl;

            delete []tablica;
            size = 0;
        }
    }

Any ideas of resolving this problem would be really worthy to me!

Answer 1

You are definitely leaking, and probably fragmenting the memory when you do this:

    int *temp = new int[size];
    if(size % 10 == 0)
    {
        for(int i = 0; i < size; i++)
            temp[i] = tablica[i];
        // Should free tablica here 
        tablica = new int[size + 10];
        for(int i = 0; i < size; i++)
            tablica[i] = temp[i];
    }

First, you allocate a temp (even if you don't need to) which is size elements, then you allocate a size+10 elements array, which is not freed.

I would suggest that you use a second variable to record the capacity, and double the capacity each time you're at the capacity. That way, you don't need 2000 allocations to grow the array to 20000 elements, but 15 re-allocations (and copies).

Answer 2

You don't show exactly how you're using the Table class, but you're probably corrupting the heap.

The test() function repeatedly pushes data onto tablica then does a delete [] tablica before doing another round of pushes.

However, when the test() function deletes tablica the last time, it doesn't set the poitner to NULL, and the Table desctuctor looks like:

~Table()
{
    delete tablica;
    size = 0;
}

So it would go ahead and delete that pointer again causing the heap to get corrupted. Note that the delete operation in ~Table() should be a delete [] tablica;.

Also, note that having the tablica pointer managed across the push_back(), test() and dtor functions makes for a messy situation.

Answer 3

Because you are leaking tablica memory. Before

tablica = new int[size + 10];

Add a line

delete []temp;

And everything would be fine.

More over in every call of push_back you are unnecessarily allocating memory in temp and deleting it. Instead allocate the memory and free inside if condition.