multiple exception definition in pg_type.h -> error compiling postgres support in Qt with gcc v3.2 (SuSE 8.1)
Your name : Frank van Vugt
Your email address : ftm.van.vugt@foxi.nl
(with thanks to Dimitri@TrollTech for his insight & examples)
System Configuration
---------------------
Architecture :
Intel Pentium III
Operating System :
Linux 2.4.19 with glibc 2.2.5 (SuSE v8.1)
PostgreSQL version :
PostgreSQL-7.2.3
Compiler used :
gcc v3.2
Please enter a FULL description of your problem:
------------------------------------------------
Postgresql itself compiles like a breeze, no problem there.
Config line: "./configure --with-openssl --with-perl --with-CXX"
Upon compiling TrollTech's Qt-library with postgresql support, the process
fails on numerous lines in pg_type.h with the following message:
In file included from sql/drivers/psql/qsql_psql.cpp:49:
/usr/src/postgresql/src/include/catalog/pg_type.h:196: declaration of
`int*
__errno_location()' throws different exceptions
/usr/src/postgresql/src/include/catalog/pg_type.h:195: than previous
declaration `int* __errno_location() throw ()'
[...]
Please describe a way to repeat the problem. Please try to provide a
concise reproducible example, if at all possible:
----------------------------------------------------------------------
The problem is caused by lines such as:
DATA(insert OID = 16 ( bool PGUID 1 1 t b ... _null_ ));
DESCR("boolean, 'true'/'false'");
Since DATA and DESCR are defined in postgres.h:
/* these need to expand into some harmless, repeatable declaration */
#define DATA(x) extern int errno
#define DESCR(x) extern int errno
These lines are eventually expanded into:
extern int errno;
extern int errno;
Obviously, compiling the following source produces the same problem:
#include <errno.h>
extern int errno;
extern int errno;
Postgresql itself seems to never include <errno.h> along with
<catalog/pg_type.h>, otherwise it would suffer from the same problem
If you know how this problem might be fixed, list the solution below:
---------------------------------------------------------------------
We might want to expand ( 'DATA', 'DESCR' ) into something else, one of them
anyway ;-)
ftm.van.vugt@foxi.nl writes:
Postgresql itself seems to never include <errno.h> along with
<catalog/pg_type.h>, otherwise it would suffer from the same problem
That's hard to believe; I think it's Qt that's doing something strange
here. Still, the ANSI C standard does discourage what we are doing:
... It is unspecified whether errno
is a macro or an identifier declared with external linkage.
If a macro definition is suppressed in order to access an
actual object, or a program defines an identifier with the
name errno, the behavior is undefined.
Seems like almost anything else would be safer than "errno" :-(
Anyone object to doing
extern int no_such_variable;
instead?
(Note that just having the macros expand to empty won't do,
because then the compiler would see a string of semicolons,
and some compilers warn about that.)
regards, tom lane
Tom Lane writes:
ftm.van.vugt@foxi.nl writes:
Postgresql itself seems to never include <errno.h> along with
<catalog/pg_type.h>, otherwise it would suffer from the same problemThat's hard to believe; I think it's Qt that's doing something strange
here.
Yeah, like compiling with thread support. ;-)
Anyone object to doing
extern int no_such_variable;
instead?
I wouldn't be surprised if some imaginative AIX linker will croak on that,
but let's try it.
--
Peter Eisentraut peter_e@gmx.net
Tom Lane writes:
That's hard to believe; I think it's Qt that's doing something strange
here.
As a newbie on the list, I'm sorry I have to disagree with you, Tom... ;)
The fact that PostgreSQL dissolves stuff into something like:
#include <errno.h>
extern int errno;
extern int errno;
was more of a suprise to me, but I could be missing something here.
Anyone object to doing
extern int no_such_variable;
instead?
I wouldn't be surprised if some imaginative AIX linker will croak on that,
but let's try it.
Well, can't say anything on that particular linker, but obviously this would
be a workable solution.
May I ask why you don't want to go with something like:
#define DESCR(x) typedef int postgresql_foo_bar
As far as Qt goes, both their next minor version as well as the next
major release will contain a workaround for this problem, something
like:
#if defined(errno)
# undef errno
#endif
#define errno qt_psql_errno
#include <catalog/pg_type.h>
#undef errno
But I guess the supposed fix will go into the PostgreSQL sourcetree?
Mind you, I don't want to start a discussion on who 'has to' solve
what where and which way is the best ;-)
Anyway, thanks a lot for the rapid responses!
Frank van Vugt
"ir. F.T.M. van Vugt bc." <ftm.van.vugt@foxi.nl> writes:
May I ask why you don't want to go with something like:
#define DESCR(x) typedef int postgresql_foo_bar
Because it doesn't work.
$ cat z.c
typedef int postgresql_foo_bar;
typedef int postgresql_foo_bar;
typedef int postgresql_foo_bar;
$ gcc -c z.c
z.c:2: redefinition of `postgresql_foo_bar'
z.c:1: `postgresql_foo_bar' previously declared here
z.c:3: redefinition of `postgresql_foo_bar'
z.c:2: `postgresql_foo_bar' previously declared here
regards, tom lane
May I ask why you don't want to go with something like:
#define DESCR(x) typedef int postgresql_foo_barBecause it doesn't work.
$ cat z.c
typedef int postgresql_foo_bar;
typedef int postgresql_foo_bar;
$ gcc -c z.c
z.c:2: redefinition of `postgresql_foo_bar'
z.c:1: `postgresql_foo_bar' previously declared here
Ah, you got me there, Tom.
Guess I had to know better than to mess with you C-guys unless I'd better make
sure I'd double-checked ;-))
Anyway, thanx again and guys are doing a great job !!
Frank.