GCC: non-conforming implementation of C++

[borophyll]

GCC allows you to define macros called "new" and "delete" in the
preprocessor phase. This seems to be in violation of the C++ spec, in
particular the rules for the creation of preprocessing tokens.
Section 2.4 of ISO/IEC 14882:2003 states that preprocessing tokens
belong to one of the following groups

preprocessing-token:
header-name
identifier
pp-number
character-literal
string-literal
preprocessing-op-or-punc
each non-white-space character that cannot be one of the
above

Section 2.12 defines a preprocessing-op-or-punc to be:

preprocessing-op-or-punc: one of
{ } [ ] # ## ( )
<: : <% % %: %:%: ; : ...
new delete ? :: . .*
+ - * / % ˆ & | ̃
! = < += -= *= /= %=
ˆ= &= |= << > >>= <<= == !=
<= >= && || ++ -- , ->* ->
and and_eq bitand bitor compl not not_eq
or or_eq xor xor_eq

Since "new" and "delete" are preprocessing-op-or-punc's, does this not
violate the spec?

Regards
B.

[goodmen]

MS vc also allow new delete be defined as macro.

in fact, MFC take use of this.

2years ago, i use mfc in my project, and found
it generate many many compile error.
Finally, I found that MFC define keyword new at the
begin of the cpp file. and i #include STL headers
behind the that definition, so the compiler is angry.

I copy/paste the stl header include before the
define, all is ok.

That is my story, don't laugh at me...............

[JohnQ]

<bo*******@gmail.comwrote in message
news:11*********************@m37g2000prh.googlegro ups.com...

"GCC allows you to define macros called "new" and "delete" in the
preprocessor phase."

That's interesting. Can some please post those macro definitions here?

John

[borophyll]

On Jul 28, 1:25 am, "JohnQ" <[e-mail]>
wrote:

"GCC allows you to define macros called "new" and "delete" in the
preprocessor phase."

That's interesting. Can some please post those macro definitions here?

This code compiles in GCC.

#include <stdio.h>
#define new 1
#define delete 2
int main()
{

printf("%d\n", new + delete);
return 0;
}

While this is a simple example, new and delete can be defined to be
any macro.

[Jack Klein]

On Fri, 27 Jul 2007 11:18:54 -0000, bo*******@gmail.com wrote in
comp.lang.c++:

GCC allows you to define macros called "new" and "delete" in the
preprocessor phase. This seems to be in violation of the C++ spec, in
particular the rules for the creation of preprocessing tokens.
Section 2.4 of ISO/IEC 14882:2003 states that preprocessing tokens
belong to one of the following groups

[snip]

Paragraph 2 of 17.4.3.1.1 Macro names forbids definition of keywords
as macros (note that new and delete are keywords). Attempting to do
so makes the program ill-formed and the behavior undefined. So the
compiler is free to do what it likes.

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://c-faq.com/
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.learn.c-c++
http://www.club.cc.cmu.edu/~ajo/docs/FAQ-acllc.html

[borophyll]

On Jul 28, 1:33 pm, Jack Klein <[e-mail]:

>
Paragraph 2 of 17.4.3.1.1 Macro names forbids definition of keywords
as macros (note that new and delete are keywords). Attempting to do
so makes the program ill-formed and the behavior undefined. So the
compiler is free to do what it likes.

Hi Jack

Thanks for the reply. I am having difficulty understanding the
relevant portion of the spec you are referring to. I think this is
the portion that you draw the above from:

"Each name defined as a macro in a header is reserved to the
implementation for any use if the translation unit includes the
header.

A translation unit that includes a header shall not contain any macros
that define names declared or defined in that header. Nor shall such a
translation unit define macros for names lexically identical to
keywords."

Correct me if I'm wrong, but doesn't this only cover the case of a
source file which includes a header? What if the file does not
include a header?

[Kai-Uwe Bux]

Jack Klein wrote:

On Fri, 27 Jul 2007 11:18:54 -0000, bo*******@gmail.com wrote in
comp.lang.c++:

>GCC allows you to define macros called "new" and "delete" in the
preprocessor phase. This seems to be in violation of the C++ spec, in
particular the rules for the creation of preprocessing tokens.
Section 2.4 of ISO/IEC 14882:2003 states that preprocessing tokens
belong to one of the following groups

[snip]

Paragraph 2 of 17.4.3.1.1 Macro names forbids definition of keywords
as macros (note that new and delete are keywords). Attempting to do
so makes the program ill-formed

So far, I am with you.

and the behavior undefined. So the compiler is free to do what it likes.

That, I don't see. The paragraph reads:

A translation unit that includes a header shall not contain any macros
that define names declared or defined in that header. Nor shall such a
translation unit define macros for names lexically identical to keywords.

It looks like a diagnosable rule to me for which a diagnostic would be
required by [1.4/1]. After that diagnostic, the compiler is free to go
ahead an translate the code anyway.
Best

Kai-Uwe Bux

[James Kanze]

On Jul 28, 1:39 am, [e-mail] wrote:

On Jul 28, 1:25 am, "JohnQ" <[e-mail]>
wrote:

"GCC allows you to define macros called "new" and "delete" in the
preprocessor phase."

That's interesting. Can some please post those macro definitions here?

This code compiles in GCC.

#include <stdio.h>
#define new 1
#define delete 2
int main()
{
printf("%d\n", new + delete);
return 0;
}

This happens to be a perfectly legal C program, so any C
compiler should compile it (and I doubt you'll find any that
don't). I imagine most C++ compilers will compile it as well,
simply because they tend to be compatible with C for this sort
of thing. Redefining a keyword by means of a macro is undefined
behavior if you include any C++ header, however (and <stdio.h>
is a C++ header, albeit a deprectated one, in a C++ program).
That doesn't mean it won't compile and run; it just means that
you have no idea what it might do.

--
James Kanze (Gabi Software) email: ja*********@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientierter Datenverarbeitung
9 place Sémard, 78210 St.-Cyr-l'École, France, [phone]

[Old Wolf]

On Jul 27, 11:18 pm, [e-mail] wrote:

GCC allows you to define macros called "new" and "delete" in the
preprocessor phase. This seems to be in violation of the C++ spec

The spec only says that such a program isn't a
valid C++ program. It doesn't mandate that a
compiler can't compile it anyway.

[James Kanze]

On Jul 28, 5:33 am, Jack Klein <[e-mail]:

On Fri, 27 Jul 2007 11:18:54 -0000, [e-mail] wrote in
comp.lang.c++:

GCC allows you to define macros called "new" and "delete" in the
preprocessor phase. This seems to be in violation of the C++ spec, in
particular the rules for the creation of preprocessing tokens.
Section 2.4 of ISO/IEC 14882:2003 states that preprocessing tokens
belong to one of the following groups

[snip]

Paragraph 2 of 17.4.3.1.1 Macro names forbids definition of keywords
as macros (note that new and delete are keywords). Attempting to do
so makes the program ill-formed and the behavior undefined. So the
compiler is free to do what it likes.

I think you're missing his point; I missed it too in an earlier
posting. The point is that according to §2.12, new and delete
are *not* keywords; they are preprocessing-op-or-punc. G++ does
complain if you try something like:
#define or &&
(or is also a preprocessing-op-or-punc).

Of course, the standard (apparently at least) contradicts itself
here, since in §2.11, it says that they are keywords (where as
or et al. explicitly aren't, but form another category:
alternate representations).

I rather think that it's an error that new and delete appear as
preprocessing-op-or-punc. They're listed as keywords as well
(and they aren't the only keywords which can be operators---the
new style casts involve a keyword as well, as does typeid).
I'll post a defect report in comp.std.c++.

--
James Kanze (GABI Software) email:ja*********@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientierter Datenverarbeitung
9 place Sémard, 78210 St.-Cyr-l'École, France, [phone]