libpq++ - How to use FieldType() ?

I am writing a graphical interface for a simple postgresql database.
Connection to the database is done with libpq++. Retrieving data from
database works fine, but when writing new or changed data back to the
database sometimes I need a possibility to get information about the datatype
of some attribute. For example I have to decide between writing a
'1234'-string or a 1234-numeric to a specific field in the database.

I understood there is a method "oid FieldType()". But I do not understand how
to use it. Is there somewhere more documentation on the net? As I am not a
professional in programming it would be most helpful for me to read some
example code.

Any help is appreciated.

Martin Graffenberger
ragraffenberger(at)gmx(dot)de