only use them with heap memory. never ever apply them to stack
try to avoid using "new and delete" if you can use shared or unique ptr
delete the a_ptr twice: from } the stack wants to delete a_ptr, from unique_ptr, heap wants to delete a_ptr too.
be cautious with line 8 comment!!!!!!!!!!!!!
https://thispointer.com/map-vs-unordered_map-when-to-choose-one-over-another/
ptr (&a) gets adjacted to be a ptr to a single byte type and then this ptr gets next byte, next byte, until it reaches sieof(a)
My own implementation:
results:
