Michael Paquier <michael@paquier.xyz> writes:
> On Thu, Feb 22, 2018 at 08:00:45PM -0500, Demitri Muna wrote:
>> Out of curiosity, how does one read a numeric type from within a C
>> extension (i.e. get a number value out of the Datum type)?
> PG_GETARG_NUMERIC(), no?
I think the core point here is that PG's "numeric" type *isn't* any
primitive C type; it's a variable-length BCD encoding. If you want
to deal with it you can, but you must spend some time reading
src/backend/utils/adt/numeric.c, as Michael suggests. If you just
want a convenient C approximation, then work with float8 and let
the implicit-coercion machinery do the conversion for you.
regards, tom lane