Determine cluster directory from Postgres service

Question

Is it possible to determine the cluster directory being used by a Postgres server, from the server itself -- i.e. the service, (under Windows) was started by something like:

C:\foo\postgres.exe -D "D:\emr\data"

Is there a SELECT query or function one can make to the running server to retrieve the value D:\emr\data?

Answer 1

(For completeness) And even shorter:

SHOW data_directory;