Re: Delete without calling destructor?

From:

"Alf P. Steinbach" <alfps@start.no>

Newsgroups:

comp.lang.c++

Date:

Fri, 01 Feb 2008 22:28:58 +0100

Message-ID:

<13q73q9mlihl443@corp.supernews.com>

* Tom1s # hilidhe:

"delete" does two things:

1) Invokes the destructor
2) Deallocates the memory

We can manually invoke the destructor with:

    p->~T();

But is there any way to manually deallocate the memory without invoking
the destructor? Something like "placement delete" perhaps? I'd be using
it where I'd be continuously constructing and destroying an object:

    T *const p = new T;

    p->~T();

    ::new(p) T;

    p->~T();

    ::new(p) T;

    p->~T();

    ::new(p) T;

    p->~T();

    ::new(p) T;

    p->~T();

    SomeSortOfPlacementDelete(p); /* Just de-allocate, don't destruct */

If you know the exact size used for the original allocation you could
perhaps use ::operator delete.

However I recommend, instead, to not do what is most likely premature
optimization.

And anyway, if measurements show you really need to avoid those
"needless" allocations and deallocations, define operator new and
operator delete for the class, and/or use an allocator more suitable for
this particular situation than the built-in one.

Cheers, & hth.,

- Alf

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