Visual studio warning C6308 exist in shrinking dynamic array

Question

Why I am getting a warning when shrinking arrays?
There is no any way of losing the pointer value.

Warning C6308 'realloc' might return null pointer: assigning null pointer to 'arr_all_guests', which is passed as an argument to 'realloc', will cause the original memory block to be leaked.

arr_all_guests = (char**)realloc(arr_all_guests,--(*guest_counter) * sizeof(char*));

Answer 1

It means that as it is written the function realloc can return a null pointer. In this case an access to all the early allocated memory will be lost

arr_all_guests = (char**)realloc(arr_all_guests,--(*guest_counter) * sizeof(char*)); 

because the original pointer arr_all_guests will be reassigned with a null pointer.

You need to use a temporary pointer as for example

char **tmp = realloc(arr_all_guests, ( *guest_counter - 1 ) * sizeof(char*)); 
if ( tmp != NULL ) 
{
    arr_all_guests = tmp;
    --*guest_counter;
}