38.10.6. Composite-Type Arguments C-language function code demo works for int, but not for numeric.

Hi.

source:
https://www.postgresql.org/docs/current/xfunc-c.html#XFUNC-C-BASETYPE
(38.10.6. Composite-Type Arguments)
column "salary" int data type works fine. But it does not work if the
"salary" column data type is numeric.

/*
rm funcs.so && rm funcs.o
gcc -I/home/jian/postgres/pg16/include/postgresql/server -fPIC -c funcs.c
gcc -shared -o funcs.so funcs.o
*/

#include "postgres.h"
#include "executor/executor.h"
#include "utils/numeric.h"

PG_MODULE_MAGIC;

PG_FUNCTION_INFO_V1(c_overaid);

Datum
c_overaid(PG_FUNCTION_ARGS)
{
HeapTupleHeader t = PG_GETARG_HEAPTUPLEHEADER(0);
Numeric limit = PG_GETARG_NUMERIC_COPY(1);
bool isnull;
Datum salary;

salary = GetAttributeByName(t,"salary",&isnull);
if(isnull)
PG_RETURN_BOOL(false);

/* alternatively, we might prefer to do PG_RETURN_NULL() for null
salary */
PG_RETURN_BOOL(DatumGetNumericCopy(salary) > limit);
}
---------------------------------------------------------------------------
then quit the session and reconnect the session.

drop table emp cascade;
create table emp(empid bigint, salary numeric, name text);
insert into emp values(1,1000,'a1');
insert into emp values(2,1100,'a2');
insert into emp values(3,1200,'a3');
CREATE OR REPLACE FUNCTION c_overaid(emp, numeric) returns boolean AS
'/home/jian/pg_ext/misc/funcs','c_overaid' LANGUAGE C STRICT;
select name, c_overaid(emp,numeric '1110') as over_paid from emp;
it returns

> name | over_paid
> ------+-----------
> a1 | t
> a2 | t
> a3 | t
> (3 rows)
>

I also tried PG_GETARG_NUMERIC,DatumGetNumeric(salary).