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Access restrictions may be imposed on any NDF identifier in order to
constrain the operations which can be performed by NDF_ routines via that
identifier.
The act of disabling a particular type of access is performed by the routine
NDF_NOACC.
For instance:
CALL NDF_NOACC( 'DELETE', INDF, STATUS )
would disable delete access for the identifier INDF.
As a result, any subsequent attempt to delete the NDF via that identifier
would fail, and the resulting error message would indicate that access had
been disabled.
Access restrictions imposed on NDF identifiers are propagated to all new
identifiers derived from them (e.g. by cloning or creation of an NDF
section).
Once imposed, they cannot be revoked.
The following types of access may be disabled, either singly or in
combination (by means of repeated calls to NDF_NOACC), in order to impose
the corresponding restriction on NDF access:
- `BOUNDS' - Disabling bounds access prevents the
pixel-index bounds of a base NDF from being altered (e.g. with the
routine NDF_SBND - §
).
The pixel-index bounds of an NDF section can always be altered
regardless of this access restriction, but the restriction will be
propagated to any new identifier obtained from an NDF section via the
routine NDF_BASE.
- `DELETE' - Disabling delete access prevents the NDF from
being deleted (e.g. with the routine NDF_DELET - §
).
- `SHIFT' - Disabling shift access prevents pixel-index
shifts from being applied to a base NDF (e.g. with the routine
NDF_SHIFT - §
).
Pixel-index shifts may always be applied to an NDF section regardless of
this access restriction, but the restriction will be propagated to any new
identifier obtained from an NDF section via the routine NDF_BASE.
- `TYPE' - Disabling type access prevents the type of any
NDF component from being altered (e.g. with the routine NDF_STYPE -
§
).
- `WRITE' - Disabling write access prevents new values from
being written to any of the NDF's components.
It also prevents the state of any of its components from being reset
(e.g. with the routine NDF_RESET -
§
).
In addition, specifying an access type of `MODIFY' in a call to NDF_NOACC
will disable all the forms of access described above.
You can enquire whether a specified type of access is available via any
identifier by using the routine NDF_ISACC.
For instance:
CALL NDF_ISACC( INDF, 'WRITE', ISACC, STATUS )
will return a logical value ISACC indicating whether write access is
available for the identifier INDF.
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Starlink User Note 33
R.F. Warren-Smith
11th January 2000
E-mail:rfws@star.rl.ac.uk
Copyright © 2000 Council for the Central Laboratory of the Research Councils