misusing placement new OR possible cxx bug

misusing placement new OR possible cxx bug

[Ralovich, Kristóf]

Hi GCC developers,

I have a c++ source, that I think is wrong (wrt the c++ standard), but
accepted by g++ (and msvc too)!

----------------------------------------

int
main(int argc, char** argv)
{
  char* d = new char[256, 256];
  return 0;
}

----------------------------------------

Is this the use of 'placement new' in weird syntax I didn't know
before, or is this code wrong and accidentally accepted by gcc? In the
former case, please correct me and sorry for the noise!


Thanks,
Kristof


PS.: my 'g++ -v' says:

Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian
4.3.2-1' --with-bugurl=file:///usr/share/doc/gcc-4.3/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr
--enable-shared --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --enable-nls
--with-gxx-include-dir=/usr/include/c++/4.3 --program-suffix=-4.3
--enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc
--enable-mpfr --enable-targets=all --enable-cld
--enable-checking=release --build=i486-linux-gnu --host=i486-linux-gnu
--target=i486-linux-gnu
Thread model: posix
gcc version 4.3.2 (Debian 4.3.2-1)

PS2.: Please CC me!

Re: misusing placement new OR possible cxx bug

[Andrew Thomas Pinski]

Sent from my iPhone

On Oct 13, 2008, at 9:10 AM, "Ralovich, Kristóf" <kristof.ralovich@gmail.co 
m> wrote:

> Hi GCC developers,
>
> I have a c++ source, that I think is wrong (wrt the c++ standard), but
> accepted by g++ (and msvc too)!
>
> ----------------------------------------
>
> int
> main(int argc, char** argv)
> {
>  char* d = new char[256, 256];
>  return 0;
> }
>
> ----------------------------------------
>
> Is this the use of 'placement new' in weird syntax I didn't know
> before, or is this code wrong and accidentally accepted by gcc? In the
> former case, please correct me and sorry for the noise!
>

This is neither.  The code is using the comma operator.

Thanks,
Andrew Pinski


>
> Thanks,
> Kristof
>
>
> PS.: my 'g++ -v' says:
>
> Using built-in specs.
> Target: i486-linux-gnu
> Configured with: ../src/configure -v --with-pkgversion='Debian
> 4.3.2-1' --with-bugurl=file:///usr/share/doc/gcc-4.3/README.Bugs
> --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr
> --enable-shared --with-system-zlib --libexecdir=/usr/lib
> --without-included-gettext --enable-threads=posix --enable-nls
> --with-gxx-include-dir=/usr/include/c++/4.3 --program-suffix=-4.3
> --enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc
> --enable-mpfr --enable-targets=all --enable-cld
> --enable-checking=release --build=i486-linux-gnu --host=i486-linux-gnu
> --target=i486-linux-gnu
> Thread model: posix
> gcc version 4.3.2 (Debian 4.3.2-1)
>
> PS2.: Please CC me!

Re: misusing placement new OR possible cxx bug

[Andreas Schwab]

"Ralovich, Kristóf" <kristof.ralovich@gmail.com> writes:

> ----------------------------------------
>
> int
> main(int argc, char** argv)
> {
>   char* d = new char[256, 256];
>   return 0;
> }
>
> ----------------------------------------
>
> Is this the use of 'placement new' in weird syntax I didn't know
> before, or is this code wrong and accidentally accepted by gcc? In the
> former case, please correct me and sorry for the noise!

$ gcc -Wunused-value -c new.cc
new.cc: In function 'int main(int, char**)':
new.cc:4: warning: left-hand operand of comma has no effect

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: misusing placement new OR possible cxx bug

[Ralovich, Kristóf]

On Mon, Oct 13, 2008 at 18:49, Andreas Schwab <schwab@suse.de> wrote:
> "Ralovich, Kristóf" <kristof.ralovich@gmail.com> writes:
>
>> ----------------------------------------
>>
>> int
>> main(int argc, char** argv)
>> {
>>   char* d = new char[256, 256];
>>   return 0;
>> }
>>
>> ----------------------------------------
>>
>> Is this the use of 'placement new' in weird syntax I didn't know
>> before, or is this code wrong and accidentally accepted by gcc? In the
>> former case, please correct me and sorry for the noise!
>
> $ gcc -Wunused-value -c new.cc
> new.cc: In function 'int main(int, char**)':
> new.cc:4: warning: left-hand operand of comma has no effect
>
> Andreas.
>
> --
> Andreas Schwab, SuSE Labs, schwab@suse.de
> SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
> PGP key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
> "And now for something completely different."
>

Thank you for the fair explanation! I have learned something new
today! I am going to find out more about 'operator comma'. BTW
-Wunused-value is quite useful!

Kristof