Re: operator new: reconciling sections 18.4 and 5.3.4(13) of the 2003
standard
On 18 Mar, 01:53, Pavel
<pauldontspamt...@removeyourself.dontspam.yahoo> wrote:
forums...@hotmail.com wrote:
Operator new as defined in Section 18.4 of the 2003 edition is as
follows:
void *operator new (size_t) throw
(std::bad_alloc); ///1
void *operator new[] (size_t) throw
(std::bad_alloc); ///2
void *operator new (size_t, const std::nothrow_t&)
throw(); ///3
void *operator new[] (size_t, const std::nothrow_t&)
throw(); ///4
Yet 5.3.4(13) states:
[unless an allocation function is declared with an
empty-exception specification (15.4), throw(), it indicates
failure to allocate storage by throwing a bad_alloc
exception (clause 15, 18.4.2.1); it returns a non-null
pointer otherwise. If the allocation function is declared
with an empty exception-specification, throw(), it returns
null to indicate failure to allocate storage and a non-null
pointer otherwise. ]
Two questions:
a) Does the reference to 'allocation function is declared with an
empty-exception specification (15.4), throw()' imply items '///3' and
'///4' as shown above?
My (in no way authoritative) reading is "no". My understanding
of 18.4 is that it simply specifies the contents of the
standard header <new> and a programmer can write as many other
overloaded (not overriding) functions for new as s/he wishes>
But he's asking here about the functions defined in the library
(which you can replace). The semantics of these functions are
in part defined by the fact that one has an empty exception
specification, and the other doesn't. And that the functions
must obey the rules of =A75.3.4.
You can, of course, provide additional overloads for operator
new, which have different semantics. They still have to obey
the more general rules of =A75.3.4: if your operator new has an
empty exception specification, it reports errors by returning a
null pointer; otherwise, it reports them by throwing bad_alloc
(or something derived from bad_alloc).
b) I'm under the impression that section 18.4 is binding, that said,
if I provide overriding definitions then those those definitions ought
to comply with 18.4. True or False?
I would say: False. The standard does not forbid defining
operator new function with 5 parameters, for example.
But such a definition wouldn't override the definitions in the
standard; it would overload them.
--
James Kanze