Re: Could anybody explain this macro for me?
On Nov 16, 11:53 pm, Old Wolf <oldw...@inspire.net.nz> wrote:
On Nov 16, 12:56 pm, James Kanze <james.ka...@gmail.com> wrote:
On Nov 15, 11:21 pm, Old Wolf <oldw...@inspire.net.nz> wrote:
On Nov 15, 11:00 pm, James Kanze <james.ka...@gmail.com> wrote:
On Nov 15, 5:04 am, Old Wolf <oldw...@inspire.net.nz> wrote:
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_CONCEPT_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:james.kanze@gmail.com
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