Can looking at freed memory cause an access violat

Question

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

Answer 1

You're asking "can" and not "will", so your answer is yes. It is undefined behavior to point to memory not owned by your program, therefore anything could happen.

Will it? Depends. That is very OS specific. You might be able to get away with it, but obviously you cannot depend on this. Trying to dereference it could cause an exception, because the OS has reclaimed the memory for it's own uses. (again, OS specific).

Answer 2

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".