[cfe-dev] Dynamic memory allocation and deleted definitions

[Rahul Jain]

Thanks David for your valuable inputs.

Hi Richard,

Any comments on this behaviour??

Thanks,
Rahul


On Wed, Nov 27, 2013 at 12:43 AM, David Blaikie <dblaikie at gmail.com> wrote:

> On Tue, Nov 26, 2013 at 10:53 AM, Rahul Jain <1989.rahuljain at gmail.com>
> wrote:
> > I think I got something relevant: Do these words make any sense in our
> > context?
>
> Not quite
>
> > An allocation or deallocation function
>
> Allocation/deallocation function does not refer to
> constructor/destructor. See 3.4p1:
>
> "A C++ implementation provides access to, and management of, dynamic
> storage via the global allocation functions operator new and operator
> new[] and the global deallocation functions operator delete and
> operator delete[]."
>
> These are actually not the ctor/dtor, in 3.4p2 their declarations are
> shown as:
>
> void* operator new(std::size_t);
> void* operator new[](std::size_t);
> void operator delete(void*);
> void operator delete[](void*);
>
> So, roughly, if you say "new T" first operator new(sizeof(T)) is
> called, then the ctor for T is called on the returned storage, if the
> T ctor throws, then operator delete is called on the storage before
> the exception is propagated (that's why even non-array "new T"
> odr-uses the deallocation function, operator delete - even though it
> doesn't/shouldn't odr-use T's dtor).
>
> > for a class is odr-used by a
> > new expression appearing in a potentially-evaluated expression as
> specified
> > in 5.3.4(New) and 12.5(Free store). A deallocation function for a class
> is
> > odr-used by a delete expression appearing in a potentially-evaluated
> > expression as specified in 5.3.5(Delete) and 12.5(Free store).
> >
> > What exactly does one mean by saying that something is odr-used?
>
> The simplistic interpretation is that if something is odr-used it must
> be defined (ie: there must be (one) definition). For example:
>
> void f1();
> void f2();
>
> int main() {
>   f1(); // odr use of f1 - the program is ill-formed if 'f1' is not defined
>   size_t s = sizeof(f2); // non-odr-use of f2 - the program is valid
> even if 'f2' is never defined
> }
>
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