Demitri Muna <postgre...@demitri.com> writes:
> I’m writing a C extension for PostgreSQL. One possible input datatype for my
> function is a numeric array, e.g. ARRAY[[1.5,2.5],[3.5,4.5]]. I can use
> “DatumGetNumeric” to extract a “Numeric” data type from the data, but at some
> point I need to convert this to a number (e.g. double) so that I can do mathy
> things with it. How does one convert a “Numeric” to, say, a double?
If you want to work with doubles, why don't you declare the function as
taking doubles?
> I have a workaround in that I can pass this to my function:
> ARRAY[[1.5,2.5],[3.5,4.5]]::float8[]
> but I’d rather have the code do that instead of bothering the user to
> remember that.
Well, the implicit coercions work in your favor in this particular case.
You can just do, eg,
regression=# create function foo(float8[]) returns float8 as
regression-# 'select $1[1]' language sql;
CREATE FUNCTION
regression=# select foo(array[1.1,1.2]);
foo
-----
1.1
(1 row)
or to emphasize that it is doing a conversion:
regression=# select foo(array[1.1,1.2]::numeric[]);
foo
-----
1.1
(1 row)
regards, tom lane
