Could anybody explain this macro for me?

[webinfinite]

#define D(y...) (const int []) {y}

My understand is that D is taking in a various length parameter y
which is an array of const int. Am I right?

Thanks.

[James Kanze]

On Nov 15, 11:21*pm, Old Wolf <oldw...@inspir e.net.nzwrote:

On Nov 15, 11:00*pm, James Kanze <james.ka...@gm ail.comwrote:

On Nov 15, 5:04*am, Old Wolf <oldw...@inspir e.net.nzwrote:

The ellipsis directly following the argument name, isn't in
any C standard. (Another poster suggests that it's a GCC
extension).

Might be. *I would certainly expect that most
implementations supporting vararg templates support it
(except maybe in their strictest modes), much like they
support a final comma in an enum list. *There is absolutely
no reason not to be orthogonal here (and I would consider
this a defect in the C standard).

Well, the gcc-3.4.4 I have here, running in standard mode,
just gives 'parse error' for:

* int foo(int x...) { }

All I get for it in 4.2.1 (the only version I have available
here) is:
varargs.cc:8: warning: control reaches end of non-void function
That's compiled with
g++ -std=c++98 -pedantic -ffor-scope -fno-gnu-keywords -foperator-
names -pipe -Wall -W -Wno-sign-compare -Wno-deprecated -Wno-non-
virtual-dtor -Wpointer-arith -Wno-unused -Wno-switch -Wno-missing-
braces -Wno-long-long -static-libgcc -ggdb3 -D_GLIBCXX_CONCE PT_CHECKS -
D_GLIBCXX_DEBUG -D_GLIBCXX_DEBUG _PEDANTIC
(my standard options).

I've never encountered this form (without the comma), and I
usually do read the list of extensions in compiler
documentation when using a new compiler. Obviously you have
more experience with compilers than I do though!

Not so much compilers. According to the first edition of _The
C++ Programming Language__ (1986), the comma isn't legal.
According to the C90 or the C++98 standard, it is optional.
I've never seen a compiler that didn't accept it either way, but
then, I don't think I'd have noticed if it didn't; I can't
remember ever actually using varargs in C++.

Since both are required by the standard, I wouldn't expect to
find support for both mentionned in the compiler documentation.

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

[Old Wolf]

On Nov 16, 12:56*pm, James Kanze <james.ka...@gm ail.comwrote:

On Nov 15, 11:21*pm, Old Wolf <oldw...@inspir e.net.nzwrote:

On Nov 15, 11:00*pm, James Kanze <james.ka...@gm ail.comwrote:

On Nov 15, 5:04*am, Old Wolf <oldw...@inspir e.net.nzwrote:
The ellipsis directly following the argument name, isn't in
any C standard. (Another poster suggests that it's a GCC
extension).
Might be. *I would certainly expect that most
implementations supporting vararg templates support it
(except maybe in their strictest modes), much like they
support a final comma in an enum list. *There is absolutely
no reason not to be orthogonal here (and I would consider
this a defect in the C standard).

Well, the gcc-3.4.4 I have here, running in standard mode,
just gives 'parse error' for:
* int foo(int x...) { }

All I get for it in 4.2.1 (the only version I have available
here) is:
* * varargs.cc:8: warning: control reaches end of non-void function
That's compiled with
* * g++ -std=c++98 -pedantic -ffor-scope -fno-gnu-keywords -foperator-
names -pipe -Wall -W -Wno-sign-compare -Wno-deprecated -Wno-non-
virtual-dtor -Wpointer-arith -Wno-unused -Wno-switch -Wno-missing-
braces -Wno-long-long -static-libgcc -ggdb3 -D_GLIBCXX_CONCE PT_CHECKS -
D_GLIBCXX_DEBUG -D_GLIBCXX_DEBUG _PEDANTIC
(my standard options).

I've never encountered this form (without the comma), and I
usually do read the list of extensions in compiler
documentation when using a new compiler. Obviously you have
more experience with compilers than I do though!

Not so much compilers. *According to the first edition of _The
C++ Programming Language__ (1986), the comma isn't legal.
According to the C90 or the C++98 standard, it is optional.
I've never seen a compiler that didn't accept it either way, but
then, I don't think I'd have noticed if it didn't; I can't
remember ever actually using varargs in C++.

Since both are required by the standard, I wouldn't expect to
find support for both mentionned in the compiler documentation.

I tried on another machine with gcc 4.0.1 .
g++ allows int foo(int x...) , gcc gives 'syntax error'.

I checked in C99 again and the grammar specification
doesn't seem to permit int foo(int x...) , the
relevant bits are:

direct-declarator:
direct-declarator ( parameter-type-list )
[snip]

parameter-type-list:
parameter-list
parameter-list , ...

Are you sure C90 allowed it?

[James Kanze]

On Nov 16, 11:53 pm, Old Wolf <oldw...@inspir e.net.nzwrote:

On Nov 16, 12:56 pm, James Kanze <james.ka...@gm ail.comwrote:

On Nov 15, 11:21 pm, Old Wolf <oldw...@inspir e.net.nzwrote:

On Nov 15, 11:00 pm, James Kanze <james.ka...@gm ail.comwrote:
On Nov 15, 5:04 am, Old Wolf <oldw...@inspir e.net.nzwrote:
The ellipsis directly following the argument name, isn't in
any C standard. (Another poster suggests that it's a GCC
extension).
Might be. I would certainly expect that most
implementations supporting vararg templates support it
(except maybe in their strictest modes), much like they
support a final comma in an enum list. There is absolutely
no reason not to be orthogonal here (and I would consider
this a defect in the C standard).
Well, the gcc-3.4.4 I have here, running in standard mode,
just gives 'parse error' for:
int foo(int x...) { }

All I get for it in 4.2.1 (the only version I have available
here) is:
varargs.cc:8: warning: control reaches end of non-void function
That's compiled with
g++ -std=c++98 -pedantic -ffor-scope -fno-gnu-keywords -foperator-
names -pipe -Wall -W -Wno-sign-compare -Wno-deprecated -Wno-non-
virtual-dtor -Wpointer-arith -Wno-unused -Wno-switch -Wno-missing-
braces -Wno-long-long -static-libgcc -ggdb3 -D_GLIBCXX_CONCE PT_CHECKS -
D_GLIBCXX_DEBUG -D_GLIBCXX_DEBUG _PEDANTIC
(my standard options).

I've never encountered this form (without the comma), and
I usually do read the list of extensions in compiler
documentation when using a new compiler. Obviously you
have more experience with compilers than I do though!

Not so much compilers. According to the first edition of
_The C++ Programming Language__ (1986), the comma isn't
legal. According to the C90 or the C++98 standard, it is
optional. I've never seen a compiler that didn't accept it
either way, but then, I don't think I'd have noticed if it
didn't; I can't remember ever actually using varargs in C++.

Since both are required by the standard, I wouldn't expect
to find support for both mentionned in the compiler
documentation.

I tried on another machine with gcc 4.0.1 .
g++ allows int foo(int x...) , gcc gives 'syntax error'.

I checked in C99 again and the grammar specification
doesn't seem to permit int foo(int x...) , the
relevant bits are:

direct-declarator:
direct-declarator ( parameter-type-list )
[snip]

parameter-type-list:
parameter-list
parameter-list , ...

Are you sure C90 allowed it?

I'll check tonight (my only copy of C90 is at home), if I
remember it, but if C99 doesn't allow it, it's highly unlikely
that C90 did; the C committee is even stricter about not
breaking existing code that is the C++ committee. (And I was
sure that C99 also allowed it, but I can't find what made me
think that in the standard.)

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