Since an NDF identifier only refers to an NDF data structure and is not itself a data structure, it is possible to have several identifiers referring to the same NDF. A duplicate identifier for an NDF may be derived from an existing one by a process called cloning, which is performed by the routine NDF_CLONE, as follows:
CALL NDF_CLONE( INDF1, INDF2, STATUS )
This returns a second identifier INDF2 which refers to the same NDF data structure as INDF1.
Cloning is not required frequently, but it can occasionally be useful in
allowing an application to ``hold on'' to an NDF when an identifier is passed to
a routine which will annul it; i.e. you simply pass the original
identifier and keep the cloned copy.
An example of this can be found in the section on matching NDF attributes
(§).