using C++ to define new functions

David Gross wrote:

Hello,

Sorry to disturb the hacker list for a question that seems not so hard.
But I got no answers elsewhere...
Is is definitively impossible to use C++ to define new SQL functions or operators
in SQL ? (I need this in order to use a big geometric library, to produce e.g. polygon
intersections, or harder).
[...]
but the linking style of c++ is rather different.
Do you have an idea ?

How about using extern "C" {...} ?

Mike

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add: Michal Mosiewicz * Bugaj 66 m.54 * 95-200 Pabianice * POLAND

Michal Mosiewicz <mimo@interdata.com.pl> writes:

David Gross wrote:

but the linking style of c++ is rather different.
Do you have an idea ?

How about using extern "C" {...} ?

I think the major problem here is that David would probably like the
constructors for any global-level variables in his C++ code to be called
when his shared library is loaded into the backend. (If his C++ code
hasn't got *any* global variables with nontrivial constructors, then
he could maybe survive without this. But it'd be a necessary part of
a general-purpose solution.)

This is doable. I routinely use a system that does dynamic loading
of C++ code (Ptolemy, http://ptolemy.eecs.berkeley.edu). It's fairly
messy and unportable however, because you have to be aware of the
machine-and-compiler-dependent conventions for naming and finding
the global constructors.

David would probably also want to link the C++ library into the backend
(as a shared library, otherwise the linker will optimize it away) so
that his shared library doesn't need to include C++ library routines.
There might be a few other little changes to make in the link that
builds the backend.

In short, this could be supported if we wanted to invest a sufficient
amount of effort in it. I'm not sure it's worth the trouble.

regards, tom lane