I am still hanging with this problem.

I am not able to make any UDF with date parameters.

As sos as I call decode_date, or decode_sql_date, or decode_timestamp in my UDF, the firebird server is killed.

I looked at the examples, coming with firebird, but they even do not work.

I made a small example. Could anyone get this to work?
Here is the content of my example UDF source file.

#include <ib_util.h>
#include <ibase.h>
#include <time.h>

ISC_TIMESTAMP * first_day (ISC_TIMESTAMP *);

/* ---------------------------*/

ISC_TIMESTAMP * first_day (ISC_TIMESTAMP * d)
{
struct tm times;
decode_timestamp(d, ×);
tm1.tm_mday = 1;
isc_encode_sql_date(&tm1, d);
return d;
}

/*
declare external function FIRST_DAY
timestamp
returns timestamp
entry_point 'first_day' module_name 'rsudf'^

*/

When I just return the input parameter, then it works:

ISC_TIMESTAMP * first_day (ISC_TIMESTAMP * d)
{
return d;
}

As soon as i use
decode_timestamp(d, ×);
it crashes the server.

Would be really great, if someone could post an example how to make a working udf for date or timestamp parameters.
I would prefere date.

How about an working example that returns a date from 3 parameters passed to it, giving day, month and year?