COBOL Manual for TNS and TNS/R Programs

Data Division
HP COBOL Manual for TNS and TNS/R Programs—522555-006
7-85
OCCURS Clause for Variable-Size Tables
At any point during execution of the object program-unit, the current value of the
depending item represents the number of occurrences in the table; therefore, its
value must never be less than min or greater than max during execution of a
statement that references the table, any of its subordinate items, or any data
structure that contains the table.
You can use the CHECK compiler directive to verify that the depending item has an
acceptable value.
•
Concept of a Variable-Size Item
Any data structure containing a variable-occurrence table has a variable size.
When such an item is referenced as an operand, its value normally includes only
those table elements whose occurrence numbers are less than or equal to the
value of the depending item at the start of the operation; however, when the data
structure is used as a receiving operand and the depending item is itself a
subordinate of the data structure (so that the operation changes its value), the size
of the receiving operand is the maximum size of the data structure; that is, the
operation proceeds as if the depending item contained the value of max.
•
Changing the Depending Item Affects Table Values
Whenever the value of the depending item is increased, occurrences of the table
are dynamically appended to each affected variable-size data structure; however,
the portion of the item’s value contained in these new occurrences has an
unpredictable content unless the same or a subsequent operation assigns a known
value to that portion.
Whenever the value of the depending item is reduced, the values of table
members whose occurrence numbers exceed the new limit are lost. Even after a
subsequent increase in the value of the depending item restores these
occurrences to the table, their values are not predictable and they must not be
used as operands until known values are assigned.
•
OCCURS DEPENDING Incompatible with REDEFINES
A variable-occurrence data item cannot be specified as a redefinition or as part of a
redefinition; that is, an OCCURS DEPENDING clause cannot appear in a data
description entry that includes a REDEFINES clause or that is subordinate to a
data description entry that includes a REDEFINES clause.
•
OCCURS DEPENDING Cannot Be Nested and Must Be Last
A data description entry with an OCCURS DEPENDING clause can only be
followed, within its record description, by descriptions of subordinate items; that is,
only one table with a variable number of occurrences can appear in a single record
description entry, and the data items it contains must be the last data items in the
record. Note, however, that a fixed-occurrence data item can be subordinate to a
variable-occurrence data item.