Обсуждение: Problem of Magic Block in Postgres 8.2

Hi,
I have some old code for extension functions in Postgres 8.0. And, I
am trying to make it work with Postgres 8.2.

One problem is about the Magic Block.
The extension functions was developed by C++ mixed with C.
The code is like:

extern "C" Datum spgistinsert(PG_FUNCTION_ARGS)
{
...
}

I have added enough PG_MODULE_MAGIC; to the source code. (Also,
include 'fmgr.h' and 'postgres.h')
But, when I create the function inside Postgres, it still complains as
following:
ERROR:  incompatible library
"/home/hepei/bin/Chameleon/lib/libspgist_trie.so": missing magic block
HINT:  Extension libraries are required to use the PG_MODULE_MAGIC macro.
STATEMENT:  /* Load the trie extension *//*------------------------ */load
'/home/hepei/bin/Chameleon/lib/libspgist_trie.so';
ERROR:  incompatible library
"/home/hepei/bin/Chameleon/lib/libspgist_trie.so": missing magic block
HINT:  Extension libraries are required to use the PG_MODULE_MAGIC macro.

I am capable to define a simple function in a single file by C, and
make it work with postgres 8.2. However, my old code is more complex,
which involves more source code, library, and it is also using both
C++ and C. So, I am not sure where the problem comes from, and how to
solve it.

Thanks
Look forward your reply
--
Pei

Pei He <hepeimail@gmail.com> wrote:

> The extension functions was developed by C++ mixed with C.
> ERROR:  incompatible library
> "/home/hepei/bin/Chameleon/lib/libspgist_trie.so": missing magic block
> HINT:  Extension libraries are required to use the PG_MODULE_MAGIC macro.

You can use extern "C" blocks for PG_MODULE_MAGIC, PG_FUNCTION_INFO_V1,
and function declarations:
   extern "C"   {   #include "postgres.h"   #include "fmgr.h"
   PG_MODULE_MAGIC;
   PG_FUNCTION_INFO_V1(your_function);   extern Datum your_function(PG_FUNCTION_ARGS);   }

However, you should very carefully use C++ exceptions and destructors
in your module because PostgreSQL uses siglongjmp; C++ unwind semantics
don't work on postgres' errors. You cannot use those C++ features and
postgres' APIs together.

Regards,
---
Takahiro Itagaki
NTT Open Source Software Center