r6:Function:stack guaranteed push
int stack_guaranteed_push( struct stack_state *ss, void *user_data );
struct stack_state *ss
- A stack state as allocated by stack_new.
- A void pointer of user data which will be pushed onto the stack.
The return value is 1 upon successful push, 0 upon failure. Failure occurs only when malloc fails.
The function stack_push fails only when the stack's freelist is empty. In this event, stack_guaranteed_push can be called, which allocates a new element and pushes using that new element, thus guaranteeing a push, barring the event of malloc failure.