free() Woes (Cont.)

The freed memory is also not being cleared in any manner - only its first bytes are altered to add it to the free list. This is why accessing memory that was just freed often does not cause a crash - all data in the chunk still contains the values it had before we freed it.

Which leads to another good rule:

If you free memory pointed to by a pointer - immediately assign NULL to this pointer, to make it easier to notice invalid use of this pointer.