g_array_sort() called but not sorting

Question

This is my code :

gint compare_ulong_function (gconstpointer a, gconstpointer b)
{
        return *(unsigned long *)a - *(unsigned long *)b;
}

GArray* build_priority_queue(unsigned char* const input_data, unsigned int const input_size)
{
    GArray* priority_queue = g_array_sized_new(FALSE, TRUE, sizeof(unsigned long), 256);

    int i;
    for (i = 0; i < input_size; i++)
            g_array_index(priority_queue, unsigned long, input_data[i])++;
    g_array_sort(priority_queue, compare_ulong_function);

    return priority_queue;

}

When I debug the g_array_sort is called (can't go into the function missing development package and can't install it) but the array isn't sorted. The compare_ulong_function is never called.

What is `input_data`? Are you sure that the `for` loop is correct? — Kerrek SB, May 23 '13 at 23:44
yes, used gdb to see if I reached the sort, input_data is a bmp file which I get by mmap. — Juskie, May 23 '13 at 23:47

score 2 · Accepted Answer · answered May 23 '13 at 23:49

As far as glib is concerned, you haven't actually added any elements to the array. You just preallocated space for them and then started accessing their memory directly (g_array_index doesn't check whether you're within bounds or not).

g_array_sort still sees the size of the array as 0. (It has space allocated for 256 elements but none have been added).

Try doing a g_array_set_size(input_size) before your loop.

Good call. The exact line added : g_array_set_size(priority_queue, input_size); — Juskie, May 23 '13 at 23:56

g_array_sort() called but not sorting

1 Answers1