Is the pointer guaranteed to preserve its value after `delete` in C++?

Question

Inspired by this question.

Suppose in C++ code I have a valid pointer and properly delete it. According to C++ standard, the pointer will become invalid (3.7.3.2/4 - the deallocation function will render invalid all pointers referring to all parts of deallocated storage).

At least in most implementations it preserves the value and will store exactly the same address as before delete, however using the value is undefined behavior.

Does the standard guarantee that the pointer will preserve its value or is the value allowed to change?

Answer 1

No, it's not guaranteed and an implementation may legitimately assign zero to an lvalue operand to delete.

Bjarne Stroustrup had hoped that implementations would choose to do this, but not many do.

http://www.stroustrup.com/bs_faq2.html#delete-zero

Answer 2

If, for whatever reason, you want to be sure the pointer variable is not changed by delete, write:

delete p + 0;

Answer 3

I believe that most implementations will keep the value, only for the sake of having no reason to change it. But regardless of whether the value is kept, it's still a useless pointer, is it not?