Tablespace monitoring Oracle 12c

Good morning,

I hope again to write in the right Space.

I have e 12C container instance with a single PDB:

Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit.

I need to query cdb_data_files (and also segments, tablespaces and some other) for monitoring pourposes.

With Oracle 10 and 11 I used to query DBA_DATA_FILES (tablespaces, segments and so on), I want informations about CDB's and PDB's occupancy so I decided to use CDB_ views.

When I connect as sysdba the query

select distinct CON_ID from cdb_data_files

shows me 1 and 3 (the single PDB) .

I created a user in the container