Problem with API (libpq) - detailed error codes

Hi!

I started programming PostgreSQL database with libpq API (client
side). It looks very easy, but unexpected I found problem, which I
cannot solve myself.
If function PQexec fails, I can get error code using PQresultStatus.
But returned codes are very generally and do not specify what really
happen. I can get detailed error description using PQerrorMessage
function, but I need detailed error code (number).

For instance, if I create table, I would like to know, that operation
failed because:
- table already exist
- sql syntax error
- invalid columnt type
and so on.

I searched documents about libpq API and even header file
'internal/libpq-int.h' but I didn't found any interesting.

I would be very gracefully for any hint.

Best regards,
Adam Bukla