Date: Sat, 3 May 2008 00:05:36 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: Steve Kargl <sgk@troutmask.apl.washington.edu> Cc: freebsd-ports@freebsd.org Subject: Re: Using stderr in an initialization? Message-ID: <20080502210536.GZ18958@deviant.kiev.zoral.com.ua> In-Reply-To: <20080502202356.GA67129@troutmask.apl.washington.edu> References: <20080502202356.GA67129@troutmask.apl.washington.edu>
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On Fri, May 02, 2008 at 01:23:56PM -0700, Steve Kargl wrote:
> I'm porting a piece of code to FreeBSD, and I've run into
> a problem that I currently don't know how to solve. I scanned
> both the Porter's Handbook and the Developer's Handbook, but
> came up empty.
>=20
> A reduce testcase is
>=20
> #include <stdio.h>
>=20
> typedef FILE *FILEP;
>=20
> static FILEP outfile =3D {stderr};
>=20
> int
> main(int argc, char *argv[])
> {
> FILE *fp;
>=20
> if (argc =3D=3D 2) {
> fp =3D fopen(*++argv, "w");
> outfile =3D fp;
> }
>=20
> fprintf(outfile, "Ouch!\n");
>=20
> return 0;
> }
>=20
> GCC gives
>=20
> troutmask:sgk[204] cc -o z a.c
> a.c:5: error: initializer element is not constant
> a.c:5: error: (near initialization for 'outfile')
>=20
> Yes, I know in the simple example above that I could
> put 'outfile =3D stderr' above the 'if (argc =3D=3D 2)'
> statement. In the much more complicated code, it isn't
> clear where such a change be made. So, anyone have a
> suggestion on how to change line 5 to satisfy gcc?
The ISO 9899 says that
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
stderr
stdin
stdout
=2E.. are expressions of type ``pointer to FILE'' that point to the FILE
objects associated, respectively, with the standard error, input, and
output streams.
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
The standards, both for the C language and SUSv3, explicitely allow for
the stderr stream designator to be an runtime-evaluated expression. This
means, it seems, that the code you included makes wrong assumption.
Speaking about the gcc-specific extensions, and still using the C
compiler, I think you may use the __attribute__((constructor)) for
some static function that would assign the stderr value to the static
variable.
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