1.5.1.8.2 "COBOL Language Reference" IBM Library Server

1.5.1.8.2 Subscripting Using Index-Names (Indexing)

Indexing allows such operations as table searching and manipulating specific items. To use indexing you associate one or more index-names with an item whose data description entry contains an OCCURS clause. An index associated with an index-name acts as a subscript, and its value corresponds to an occurrence number for the item to which the index-name is associated.

The INDEXED BY phrase, by which the index-name is identified and associated with its table, is an optional part of the OCCURS clause. There is no separate entry to describe the index associated with index-name. At run time, the contents of the index corresponds to an occurrence number for that specific dimension of the table with which the index is associated.

The initial value of an index at run time is undefined, and the index must be initialized before it is used as a subscript. An initial value is assigned to an index with one of the following:

The PERFORM statement with the VARYING phrase
The SEARCH statement with the ALL phrase
The SET statement

The use of an integer or data-name as a subscript referencing a table element or an item within a table element does not cause the alteration of any index associated with that table.

X As an IBM extension, an index-name can be used to reference any table.
X However, the table element length of the table being referenced and of the
X table that the index-name is associated with should match. Otherwise, the
X reference will not be to the same table element in each table, and you
X might get run-time errors.

Data that is arranged in the form of a table is often searched. The SEARCH statement provides facilities for producing serial and non-serial searches. It is used to search for a table element that satisfies a specific condition and to adjust the value of the associated index to indicate that table element.

To be valid during execution, an index value must correspond to a table element occurrence of neither less than one, nor greater than the highest permissible occurrence number.

For more information on index-names, see "INDEXED BY Phrase" in topic 5.3.10.3.

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1.5.1.8.2 Subscripting Using Index-Names (Indexing)

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