Thread

1. Extending PostgreSQL in C or C++

   Sebastien Lemieux <slemieux@elitra.com> — 2003-06-17T20:36:08Z

   Hi,
   
     I need to extend postgreSQL to support some specific function I will 
   code in C (ideally C++ if it can work!).  I'm trying to run some simple 
   test and it doesn't seem to work.  Here is the C code:
   
   ----------
   #include "postgres.h"
   #include <string.h>
   
   int
   add_one(int arg)
   {
     return arg + 1;
   }
   ----------
   
   Which is compiled with:
   gcc -fpic -c -I/[ThePath]/postgresql-7.3.2/include/server/ pgsql_bio.c
   gcc -shared -o pgsql_bio.so pgsql_bio.o
   
   It compiles fine.
   
   And then in postgreSQL as user postgres in database template1:
   CREATE FUNCTION add_one(int4) RETURNS int4
        AS '/[PathToTheObject]/pgsql_bio.so' LANGUAGE C
        WITH (isStrict);
   
   Then I get:
   ERROR:  Can't find function add_one in file /[PathToTheObject]/pgsql_bio.so
   
   I'm using PostgreSQL 7.3.2 on Redhat 7.2 (linux 2.4.7-10) and compiling 
   with gcc 2.95.3.
   
   Following some suggestions I found on usenet, I ran 'nm' on the library 
   and I got the expected entry for my function:
   00000700 T add_one
   
   Anyone has an idea about what I am doing wrong?  Any suggestion will be 
   welcome!
   
   thanks,
   
   -- 
   Sebastien Lemieux
   Bioinformatics, post-doc
   Elitra-canada
   
   
   

2. Re: Extending PostgreSQL in C or C++

   David Blasby <dblasby@refractions.net> — 2003-06-17T21:13:19Z

   Sebastien Lemieux wrote:
   > Hi,
   > 
   >   I need to extend postgreSQL to support some specific function I will 
   > code in C (ideally C++ if it can work!). 
   
   Be very carefull with using C++ functions inside postgresql.  If the C++ 
   code throws an exception the postgresql backend will get a SIGABRT and 
   terminate.
   
   You can solve this by linking the std c++ library to the postmaster.  We 
   tried everything we could think of to fix this, but this was the only 
   solution that worked.
   
   For a complete discussion, you can read the PostGIS (GIS spatial objects 
   for Postgresql) mailing list (http://postgis.refractions.net) and the 
   GEOS (Geometry Engine, Open Source) mailing list 
   (http://geos.refractions.net).
   
   dave
   
   
   

3. Re: Extending PostgreSQL in C or C++

   Tom Lane <tgl@sss.pgh.pa.us> — 2003-06-17T21:42:23Z

   Sebastien Lemieux <slemieux@elitra.com> writes:
   > Then I get:
   > ERROR:  Can't find function add_one in file /[PathToTheObject]/pgsql_bio.so
   
   Hmm.  I can't see anything wrong with what you did, either.
   
   It's possible that the dynamic linker has printed additional messages to
   the backend's stderr.  Make sure that you have stderr set up to go
   someplace useful (not /dev/null) and look there to see if you can learn
   more.
   
   			regards, tom lane
   
   

4. Re: Extending PostgreSQL in C or C++

   Andreas Pflug <andreas.pflug@web.de> — 2003-06-17T21:51:34Z

   David Blasby wrote:
   
   > Sebastien Lemieux wrote:
   >
   >> Hi,
   >>
   >>   I need to extend postgreSQL to support some specific function I 
   >> will code in C (ideally C++ if it can work!). 
   >
   >
   > Be very carefull with using C++ functions inside postgresql.  If the 
   > C++ code throws an exception the postgresql backend will get a SIGABRT 
   > and terminate.
   >
   > You can solve this by linking the std c++ library to the postmaster.  
   > We tried everything we could think of to fix this, but this was the 
   > only solution that worked.
   >
   > For a complete discussion, you can read the PostGIS (GIS spatial 
   > objects for Postgresql) mailing list (http://postgis.refractions.net) 
   > and the GEOS (Geometry Engine, Open Source) mailing list 
   > (http://geos.refractions.net).
   >
   If you try C++, you will find some nasty name/reserved words collisions, 
   but it will work:
   
   #define using __using
   #define typeid __typeid
   #define typename __typename
   #define namespace __namespace
   #define delete __delete
   extern "C"
   {
   #include "postgres.h"
   #include "executor/spi.h"
   #include "funcapi.h"
   }
   #undef using
   #undef typeid
   #undef typename
   #undef namespace
   #undef delete
   
   Fortunately, my code didn't use exceptions...
   Regards,
   Andreas
   
   
   
   

5. Re: Extending PostgreSQL in C or C++

   Christof Petig <christof@petig-baender.de> — 2003-06-18T10:57:45Z

   Tom Lane wrote:
   > Sebastien Lemieux <slemieux@elitra.com> writes:
   > 
   >>Then I get:
   >>ERROR:  Can't find function add_one in file /[PathToTheObject]/pgsql_bio.so
   > 
   > 
   > Hmm.  I can't see anything wrong with what you did, either.
   > 
   > It's possible that the dynamic linker has printed additional messages to
   > the backend's stderr.  Make sure that you have stderr set up to go
   > someplace useful (not /dev/null) and look there to see if you can learn
   > more.
   
   most likely he has to declare the function as extern "C". A nm 
   pgsql_bio.so can tell more.
   
       Christof