Post mortem minidump debugging In windbg -- what causes <memory access error> for heap memory?

Question

I'm looking at a crash dump. Some variables seem perfectly viewable in windbg, while others just say "memory access error". What causes this? Why do some variables have sensical values while others simply list ?

It appears that all the problems are associated with following pointers. I'm certain that while many of these pointers are uninitialized the vast majority of them should be pointing somewhere valid. Based on the nature of this crash (a simple null ptr dereference) I'm fairly certain the whole process hasn't gone out to lunch.

Answer 1

If they are local pointer variables, what is most likely happening is that the pointers are not initialized, or that stack location has been reused to contain another variable, that may not be a pointer. In both cases, the pointer value may point to a random, unreadable portion of memory.