Question

I have functon that convert list in array:

void* list_to_array(SList* list)
{
     int i;
     int array_size = list_get_length(list);

     void* array[array_size];

     for (i = 0; i < array_size; i++)
     {
      array[i] = list_get_n_data(list,i);
     }

     return *array;
}

But when i try to test it:

int* a = (int*)list_to_array(list);
printf("%d" (int)a);

it’s ok. I see first element. But when i try to get second or third element:

int* a = (int*)list_to_array(list);
a++;
printf("%d" (int)a);

I see first element + 4. if i try get third element i see first element value + 8 and etc… Why? What’s wrong?

Thank you

Answer 1

You are returning a pointer to a stack memory location. That memory region is no longer valid once the function returns.

Also, instead of actually returning a pointer to the array, you are returning the first element in the array. The following code will return 1, not a pointer the array.

int array[] {1, 2, 3, 4};
return *array

You probably only need to make minimal changes your code to get it to work.

void** array = (void **) malloc(sizeof(void *) * array_size); 
...
return array;

Just make sure that you release the memory that memory used for array when you are finished with it.

void **array = list_to_array(list);
// Use array
...
// Finished with array
free(array);