If you just want to perform some operations on an existing HDS object using basic HDS subroutines, you need an HDS locator (see SUN/92) for the object and usually you will want to specify the name of the object as a parameter of the program.
The DAT_ASSOC
routine will associate an object with a program parameter and return a locator for it.
The association can be cancelled and the locator annulled by calling DAT_CANCL
.
If DAT_ASSOC
fails to associate the parameter with an object it will report the problem and
prompt for a new value. It will do this up to five times before giving up and returning status
PAR__NULL
.
DAT_EXIST
is similar to DAT_ASSOC
but it will return immediately if the association fails. It can therefore
be used to test for the existence of an object. Status PAR__ERROR
(not DAT_EXIST
, for historical reasons)
will be returned if the object does not exist, but the parameter value will not be cancelled so a
subsequent HDSPAR subroutine call (such as DAT_CREAT
) specifying the same parameter
would not prompt for a new object name. See the example in Section 10 for an illustration of
this.
The ACCESS
Field (see SUN/115) specified in the Interface Module for the program must be compatible
with the access mode specified in the DAT_ASSOC
or DAT_EXIST
call, otherwise status SUBPAR_ICACM
will
be returned.
Both routines may be called more than once for the same parameter but DAT_CANCL
must be called to
cancel an existing association if a different object is required (see ‘Parameter States’, Section
3).