Thread: Load C++ for functions?

I'm trying to link up a C++ project with postgres functions, the following code compiles (as C++):

extern "C" {
    #include <postgres.h>
    #include <fmgr.h>

    #ifdef PG_MODULE_MAGIC
    PG_MODULE_MAGIC;
    #endif
};

extern "C" {
    PG_FUNCTION_INFO_V1(pg_xversion);
};
extern "C" Datum pg_xversion(PG_FUNCTION_ARGS)
{
    PG_RETURN_NULL();
}

But the CREATE FUNCTION gives the error:
ERROR:  could not load library "/storage/Scripts/pgx/pgx.so": /storage/Scripts/pgx/pgx.so: undefined symbol:
__gxx_personality_v0

Postgres is no doubt trying to load a C++ linked library as C - is there a way to fix this?

Hey Elliot,

See http://www.postgresql.org/docs/9.0/static/extend-cpp.html

Probably compiling with -fno-exceptions solve you problem.




--
// Dmitriy.

Cheers! It works.

On 12/24/2010 10:29 PM, Elliot Chance wrote:

> But the CREATE FUNCTION gives the error:
> ERROR:  could not load library "/storage/Scripts/pgx/pgx.so": /storage/Scripts/pgx/pgx.so: undefined symbol:
__gxx_personality_v0

How'd you build the C++ code? What was your compile command line? Does
'ldd pgx.so' list libstdc++ as a dependency? Are you for some reason
compiling with -fno-exceptions? Is every single one of your C++
functions wrapped with an unconditional try/catch that converts any
exceptions to error return codes/Pg elog() calls?

I've written Pg extension modules, but I've always done so by compiling
the component containing PG_MODULE_MAGIC, PG_FUNCTION_INFO_V1,
PG_FUNCTION_ARGS, etc as regular C, and having it call "extern C"
functions in the C++ files linked into the shared object. I don't
*think* this should make any difference, but I'm far from a C/C++ expert.

> Postgres is no doubt trying to load a C++ linked library as C - is there a way to fix this?

AFAIK, dlopen() doesn't care if a library is C, C++, or BlueLanguage, so
long as it provides standard ELF symbols and a C-compatible entry point.

--
Craig Ringer

On 12/24/2010 11:16 PM, Elliot Chance wrote:
> Cheers! It works.

Beware - that's really unsafe if you're calling C++ libraries that may
throw exceptions.

--
Craig Ringer