Undefined behavior or not?

[Segher Boessenkool]

On Sat, Mar 11, 2017 at 04:38:56PM +0100, onkel.jack@t-online.de wrote:
> Dont mess up p and (*p).
> 
> Its true the the content of the memory p points to may change after free, depending on what other threads do and what the operating system is doing on free.
> but the value of p, which contains the address of the allocated memory, does not change at free.
> Its till holds that address.
> 
> This means, p stay as is but *p may change.

No, that is not how it works.  6.2.4/2 says: [...] "The value of a
pointer becomes indeterminate when the object it points to (or just
past) reaches the end of its lifetime."

It does not matter whether the value of p changes in *your* system,
or in most systems.  Using the value of p after deallocating the object
it pointed to is undefined behaviour.


Segher