Does the C++ standard define what should happen in case of NULL pointer
dereferencing. If not, does it say that it is illegal?
Where, if so, does it say it?
Jul 23 '05
51  3196 
ajitho wrote: #include <stdio.h>
[..]
void main() {
[.. example of undefined behaviour snipped ..]
Yes, we get it, you know how to reproduce undefined behaviour.
Give it a rest already.
ajitho wrote: ...
What are you trying to demonstrate by posting these already
beaten-to-death examples here? Both code samples you posted so far
produce undefined behavior. Are you trying to say that sometimes
undefined behavior might manifest itself in seemingly predictable
manner? But we all know that. And it is completely irrelevant and
doesn't make any difference.
--
Best regards,
Andrey Tarasevich
How about this:
Look at the definition of the "offsetof" macro in whatever C/C++
compiler you use.
It is obviously dereferencing a null pointer. It is not making use of
the <b>value</b> of the dereference. There is a suble difference.
ajitho wrote: How about this:
Look at the definition of the "offsetof" macro in whatever C/C++
compiler you use.
It is obviously dereferencing a null pointer. It is not making use of
the <b>value</b> of the dereference. There is a suble difference.
It is also part of the standard library, not user code. The writer of
the standard library can take advantage of knowledge of compiler details
that users cannot portably rely on.
--
Pete Becker
Dinkumware, Ltd. ( http://www.dinkumware.com)
Pete Becker wrote: ajitho wrote: How about this:
Look at the definition of the "offsetof" macro in whatever C/C++
compiler you use.
It is obviously dereferencing a null pointer. It is not making use
of the <b>value</b> of the dereference. There is a suble difference.
It is also part of the standard library, not user code. The writer of
the standard library can take advantage of knowledge of compiler
details that users cannot portably rely on.
For example, the X window system defines XtOffset(type, member) in
several different ways. ONE of those ways is ((type*)NULL)->member.
However, it is not the only one, indicating that at least on some
systems that doesn't work as planned.
Of course, that is C code, but I don't think there is a difference in
this case.
I'm sure you know much more about the language than me. I thought the
"grey area" was legal .... (Falling back on the reasoning that the
dereferenced data is not actually accessed -- we're just playing around
with its address).
You're probably right ....
On Tue, 15 Feb 2005 12:07:59 -0800, Andrey Tarasevich
<an************ **@hotmail.com> wrote: ajitho wrote: http://www.comeaucomputing.com/iso/cwg_closed.html#315
And? Have you tried to follow the link and read the DR#315 yourself?
Have you ever heard about the difference between static and no-static
members of the class?
Also, try reading
http://www.comeaucomputing.com/iso/cwg_active.html#232
http://www.comeaucomputing.com/iso/cwg_active.html#453
linked from DR#315.
In your first example the function is not static. The behavior is
undefined regardless of what the outcome of these still open DRs.
In your second example you are trying to create a null-reference. This
is undefined behavior. And if you read the proposed resolutions in the
above DRs, you'll see that there's no intent whatsoever to legalize
null-references in C++. The behavior is undefined.
I think it's some weird kind of troll. I thought originally that it was
just confused (which is not an unusual state), but just posting examples
of undefined behaviour is weird...
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