Incomplete example from Accelerated c++

[Paul]

Accelerated c++ contains the code below which is discussed for the case n = 0.
If n = 0, I can see that v is an empty vector but I don't see what effect the delete statement has.
The delete statement deletes the iterator one past the end of an empty vector. This seems similar to deleting a null pointer but is not quite the same.
I would think that the delete statement does nothing in the same way that deleting a null pointer does nothing. However, I can't find anything that explicitly says so. Thank you.

Paul

T* p = new T[n];
vector<T> v(p, p + n);
delete[] p;

[Luca Risolia]

On 16/03/2015 16:28, Paul wrote:
> Accelerated c++ contains the code below which is discussed for the
> case n = 0. If n = 0, I can see that v is an empty vector but I don't
> see what effect the delete statement has. The delete statement
> deletes the iterator one past the end of an empty vector. This seems
> similar to deleting a null pointer but is not quite the same. I would
> think that the delete statement does nothing in the same way that
> deleting a null pointer does nothing. However, I can't find anything
> that explicitly says so. Thank you.

> T* p = new T[n]; delete[] p;

If I remember well, if n = 0, by standard p cannot be nullptr, but
delete should be safe. You should have a look at the standard for the
exact wording.

[Paavo Helde]

Paul <peps...@gmail.com> wrote in
news:210d9637-2b53-4cdb...@googlegroups.com:

p is a pointer to an object allocated by new[], so of course it is safe to
delete[] it. And delete[] works on pointers, not iterators, so whether p
can be interpreted in another context as an iterator or not is besides the
point. Comment out the unneeded second line if this is confusing you.

[Bo Persson]

The standard says (in §18.6):

"Required behavior: Return a non-null pointer to suitably aligned
storage (3.7.4), or else throw a bad_alloc exception."

So even if you allocate space for zero elements, you still get a valid
pointer to these zero elements (and possibly for some additional
bookkeeping info).



Bo Persson