Question

int arr2[5]={5,4,3,2,1};
sortArray(arr2, 5);

void sortArray(int data[], int size)
{
    int i, j;
    int element;

    for (i = 1; i < size; i++)
    {
        element = data[i];
        j = i-1;

        while (j >= 0 && element < data[j])
        {
            data[j+1] = data[j];
            j--;
        }

        data[j] = element;
    }
}

My function gets this error and my array look like this {5,5,5,5,5} when the function ends, why so?

Answer 1

As stated above: during the first iteration of your for loop, after the while loop has executed, j is decremented to -1 and then used in as the index in your data array; this is the cause of your stack corruption.

Some more info about stack corruption: when you reference a certain index of your array (IE data[j]), you’re basically saying ‘start at the location in memory pointed to by the pointer named data, add j * sizeof(int) bytes, and grab that value’.

In code, data[j] is equivalent to *(data + (j * sizeof(int))). When you give a negative value, you reference memory not allocated to the data array; in this case the memory happens to be part of the stack. Because you’re modifying it, you get the stack corruption error.