COBOL: Indexed BY Vs USAGE Vs OCCURS

The COBOL occurs, Usage is Index, Indexed By clause are tricky. And these are confused by many people. In this post, I have shared three key points:

1. OCCURS
2. Indexed BY
3. Usage is Index

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1). COBOL Occurs

COBOL programmers confused very much about how to use the OCCURS clause with the KEY phrase correctly. The syntax for OCCURS clause with Indexed BY

01 GROUP-ITEM.
 03 ITEM-A OCCURS 7 TIMES INDEXED BY IX.
 05 NAME PIC X(20).
 05 ADDRESS-1 PIC X(20).
 05 ADDRESS-2 PIC X(20).
 05 ADDRESS-3 PIC X(20).
 05 CITY PIC X(20).
 05 STATE PIC XX.
 05 ZIP PIC 9(5).
 …
 PERFORM VARYING IX FROM 1 BY 1 UNTIL IX > 7
 DISPLAY NAME(IX),CITY(IX),STATE(IX),SPACE,ZIP(IX)
 END-PERFORM.

2). COBOL Index

Indexed is different from the index data item (Usage is an index). This post gives you a complete idea.

About Index in TABLE ARRAY

• An index name (or just index) is an item that contains a value corresponding to an occurrence number of the table with which it is associated.
• Index(IX) is not necessarily stored in memory as an integer.
• A COBOL vendor may choose to implement it as a pointer to an element of the table, an offset from the beginning of the table, or whatever representation seems convenient for a particular COBOL implementation.
• The purpose of the index is to make accessing a table as efficiently as possible.

In simple words:

• The index is different from the Index data item
• The index is not required to define explicitly in the COBOL program
• The index is associated with a Table on which it is mentioned
• The index is not an identifier. So, the index is not an Integer
• Index names you can use as variables in PERFORM, SET, and SEARCH Statements

You are now good with what is an index. Now, I will share the key points on what is an index data item.

3). Usage is Index Data Item:

01 INDEX-1  USAGE is INDEX.
or
77 INDEX-1  USAGE is INDEX.

Benefits of Usage is Index Data item

1. Number one benefit is, you can pass the Usage-is-index data item to a SUBPROGRAM (the indexed-value you cannot pass to the sub-program)
2. The other benefit is, you can write the usage-is-index data items to a file.
3. How we use Index the same way you can use usage is an index data item.

How to Display Usage is Index data item

DISPLAY INDEX_1.

4). How to Define Key

Ascending/Descending Key is XYZ.

Table definition with Multiple KEYS:

01 MAIL-INFO.
 03 MAIL-LIST OCCURS 1000 TIMES
     ASCENDING KEY IS STATE, CITY.
     05 NAME          PIC X(20).
     05 ADDRESS       PIC X(20) OCCURS 3 TIMES.
     05 CITY          PIC X(20).
     05 STATE         PIC XX.
     05 ZIP          PIC 9(5).

Interview Question on Keys:

• By specifying ascending/descending Key IS, it doesn’t mean that the Table is in sorted order. This is only an expected order.

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