The following documentation comment has been logged on the website:
Page: https://www.postgresql.org/docs/10/static/libpq.html
Description:
It should be mentioned, that the function PQfmod is not applicable for a
valid PGresult returned by PQdescribePrepared.
PQfmod delivers additional information for datatypes of variable size, like
maximum size for varchar or precision/scale for numeric.
This information is currently not available for parameters of prepared
statements. On the other hand, for example: users of the binary interface
should not experience any errors
when providing correct binary data for a numeric parameter: if the
specified scale does not match with the scale of the related numeric column
in the database table, then postgres will handle it correctly and round it
as needed.