postgres functions and C++

Hello all,

Please help me with
create function days_in_month(int4, int4, int4) returns int4
as '/tmp/days.so' language 'c';

Can I write this function days_in_month in C++ ?
I've did the following:

extern "C" {
int days_in_month(int year, int mo, int day);
}

extern "C" {
int days_in_month(int year, int mo, int day) {
═══ return 13;
}
}

Compile with
$ g++ -I/usr/local/qt/include -o days.so -shared days.cpp

then (as user postgres)
my=> create function days_in_month(int4, int4, int4) returns int4
my=> as '/tmp/days.so' language 'c';
CREATE

I've tried to use new function
my=> select days_in_month(3, 3, 3);
ERROR:═ Can't find function days_in_month in file /tmp/days.so
my=>

What is wrong ?
I'm using postgres 6.4 under RedHat.
Any help will be appreciated.

--
Best regards,
Vladimir mailto:gsmith(at)eurocom(dot)od(dot)ua