Removing an item from the head our list

Of course, we again need to be careful about the case of the empty list:

char *remove_item(void)
{
    LISTITEM *old = list;
    char     *string;

    if(old == NULL) {
        fprintf(stderr, "cannot remove item from an empty list\n");  
        exit(EXIT_FAILURE);
    }

    list   = list->next;
    string = old->string;
    free(old);

    return string;
}

We say that the caller now owns the storage required to hold the string - even though the caller did not initially allocate that storage.

It will be up to the caller to deallocate that memory when no longer required.
Failure to deallocate such memory can lead to memory leaks, that may eventually crash long running programs.