Can looking at freed memory cause an access violation?

Question

Can accessing (for read only) memory freed cause an access violation, and, if so, under what circumstances?

Answer 1

Yes, it can. "Access violation" ("segmentation fault", etc) is the response that is normally generated by OS/hardware when the process attempts to access (even just for reading) memory that is known to OS as "empty", "freed" or inaccessible for some other reason. The key moment here is that the OS/hardware must know that the memory is free. Memory management functions of C Standard Library don't necessarily return the 'free'd memory back to OS. They might (and will) keep it for future allocations. So in some cases accessing 'free'd memory will not result in "Access Violation" since from the OS's/hardware's point of view this memory has not been really freed. However, at some point the Standard Library might decide to return the collected free memory back to OS, after which an attempt to access that memory will normally result in "Access Violation".