[postgis-users] Linking to the PostGIS library

Nathaniel naptrel at yahoo.co.uk
Thu Nov 16 07:26:41 PST 2006

On 16 Nov 2006, at 09:10, strk at refractions.net wrote:

> Missing -llwgeom ?
> Also -rpath might be useful as liblwgeom is likely *not* in your
> default path.
> Check with 'ldd' (or whatever apple changed it to)

Thanks strk for the reply. I used your suggestions to fuel more  
internet searches, and it seems it's not that simple on the mac  
(anyone surprised?) In case someone in the future has similar  
problems and stumbles upon this thread, here's what I've found so far:

On the mac, postgres needs what Apple calls a "bundle" (aka "loadable  
module"), which is a form of dynamic library. This is a tad different  
from your standard unixian shared lib. For one, bundles seem to have  
a significant limitation: you can't link against them (at least  
according to <http://fink.sourceforge.net/doc/porting/shared.php> )!  
This explains why I've struggled for hours to build my  
library...achem, I mean bundle....against the PostGIS liblwgeom.so  

You can build proper, dynamic shared libs on the mac (using - 
dynamiclib flag to gcc). The generic Postgres module makefile  
(Makefile.shlib), as used by PostGIS, even teasingly comes with a  
flag (DLTYPE), that if set to "library", looks as though it should  
build one of these. So I thought, if I could build PostGIS as a  
proper dynamic, shared library rather than a bundle, I could link my  
code against it. (I didn't care if I had to have both liblwgeom.so  
and liblwgeom.dylib sitting in /usr/local/pgsql/lib/, the former for  
function calls to the postgis module, the latter for calls to mine).

Permitting myself to hack only a handful of lines I couldn't get  
PostGIS to successfully build a ".dylib" that I could build against.  
Changing lots of build or source code would make upgrading PostGIS  
prohibitively time-consuming.

But I did find a simple, if less-than-satisfactory, one line  
solution: merge my library (compiled into myfoo.o, say) into the  
PostGIS build!

In lwgeom/Makefile:

OBJS=$(SA_OBJS) liblwgeom.o [...] long_xact.o myfoo.o

Then, change my SQL function definitions to point to "liblwgeom"  
rather than "libmyfoo" and I'm off. Thanks again
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