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.

[Old Wolf]

On Nov 13, 12:46*pm, "webinfin...@gm ail.com" <webinfin...@gm ail.com>
wrote:

#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?

This is a syntax error. Are you sure you transcribed
it correctly?

[Juha Nieminen]

Old Wolf wrote:

On Nov 13, 12:46 pm, "webinfin...@gm ail.com" <webinfin...@gm ail.com>
wrote:

>#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?

This is a syntax error. Are you sure you transcribed
it correctly?

To me it looks like a variadic macro from the newer C standard, not
yet in the C++ standard.

[Ian Collins]

we*********@gma il.com wrote:

#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?

Try c.l.c, this looks like C99.

--
Ian Collins

[Tim H]

On Nov 12, 7:06*pm, Ian Collins <[e-mail] mwrote:

webinfin...@gma il.com wrote:

#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?

Try c.l.c, this looks like C99.

--
Ian Collins

That's not any C99 syntax I know of, either. C99 provides __VA_ARG__
for variadic macros.

[James Kanze]

On Nov 13, 1:28 am, Juha Nieminen <nos...@thanks. invalidwrote:

Old Wolf wrote:

On Nov 13, 12:46 pm, "webinfin...@gm ail.com" <webinfin...@gm ail.com>
wrote:

#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?

This is a syntax error. Are you sure you transcribed it
correctly?

To me it looks like a variadic macro from the newer C
standard, not yet in the C++ standard.

There are actually two things in the above which cause syntax
errors in current C++. The first is that it is a variadic
macro, which is legal in C99 and will be legal in the next
version of C++. The second is that when expanded, this results
in a compound literal. Again, C99, but not current C++; in this
case, I know that the next version will extend the
initialization syntax, but I'm not sure whether the extension
will look exactly like a compound literal in C or not.

--
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 13, 11:04*pm, James Kanze <james.ka...@gm ail.comwrote:

On Nov 13, 1:28 am, Juha Nieminen <nos...@thanks. invalidwrote:

Old Wolf wrote:

On Nov 13, 12:46 pm, "webinfin...@gm ail.com" <webinfin...@gm ail.com>
>
>#define D(y...) (const int []) {y}

There are actually two things in the above which cause syntax
errors in current C++. *The first is that it is a variadic
macro, which is legal in C99 and will be legal in the next
version of C++. *

Variadic macros in C99 look like:

#define D(y, ...)

i.e. the ellipsis is separated from the other
arguments by a comma (with optional whitespace).

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

[James Kanze]

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

On Nov 13, 11:04*pm, James Kanze <james.ka...@gm ail.comwrote:

On Nov 13, 1:28 am, Juha Nieminen <nos...@thanks. invalidwrote:

Old Wolf wrote:
On Nov 13, 12:46 pm, "webinfin...@gm ail.com" <webinfin...@gm ail.com>

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

There are actually two things in the above which cause syntax
errors in current C++. *The first is that it is a variadic
macro, which is legal in C99 and will be legal in the next
version of C++. *

Variadic macros in C99 look like:

* #define D(y, ...)

i.e. the ellipsis is separated from the other
arguments by a comma (with optional whitespace).

So I see. I wonder why they didn't support the form without the
comma, as they do in function declarations. Shocking lack of
orthogonality.

(Historically, the comma wasn't allowed in function
declarations; the syntax was exactly that of a natural language,
where you would never write "a, b, ..." but always "a, b...".
When C adopted this syntax from C++, the C committee decided to
allow the syntax with the comma as well; I'm not sure what their
reasoning was, but I also find it more appealing, separating the
.... from the preceding argument. But not enough more appealing
to have justified changing or extending the existing
specification; if it were a new invention, I'd define it with
the comma, but since it wasn't, and isn't, I don't think that
there was, or is, sufficient justification to add the form with
the comma.)

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).

--
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]

[Juha Nieminen]

Old Wolf wrote:

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

Straight from the horse's mouth:

http://gcc.gnu.org/onlinedocs/cpp/Variadic-Macros.html

[Old Wolf]

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...) { }

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!