Re: Null references.

[Pete Becker]

On 2008-07-15 23:04:29 -0400, "Alf P. Steinbach" <al***@start.nosaid:

>
There are some exceptions to incurring UB for dereferencing a
nullpointer. The most important one is that any given compiler vendor
can decide to give that a well-defined meaning at compile time for that
compiler, and exploit that to implement various macros in the standard
library.

That is not an exception to the meaning of undefined behavior. The
language definition says that certain things result in undefined
behavior, and that means that the language definition doesn't tell you
what those things do. The possiblity that a particular compiler vendor
makes some of those things well defined doesnt change the fact that the
language definition doesn't impose requirements. The behavior is still
undefined.

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)

[Pete Becker]

On 2008-07-16 17:36:59 -0400, "Alf P. Steinbach" <al***@start.nosaid:

* Pete Becker:

>On 2008-07-15 23:04:29 -0400, "Alf P. Steinbach" <al***@start.nosaid:

>>>
There are some exceptions to incurring UB for dereferencing a
nullpointer. The most important one is that any given compiler vendor
can decide to give that a well-defined meaning at compile time for that
compiler, and exploit that to implement various macros in the standard
library.

That is not an exception to the meaning of undefined behavior. The
language definition says that certain things result in undefined
behavior, and that means that the language definition doesn't tell you
what those things do. The possiblity that a particular compiler vendor
makes some of those things well defined doesnt change the fact that the
language definition doesn't impose requirements.

Agreed, up till this point. I was talking about incurring UB and
you're talking about the meaning of UB.

I don't know what "incurring UB" means. The standard simply says that
the behavior of the program is undefined, not that anyting incurs
anything.

>

>The behavior is still undefined.

No, of course it isn't: it's then only undefined with respect to the standard.

It may do what some implementor says it does. That doesn't change the
fact that it's undefined behavior. If you're using the term "undefined
behavior" to mean something other than what the standard says it means,
you need to say so.

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)