PICTURE clauses and how data is stored

The PIC clause says what a field holds and how big it is. The USAGE says how it is physically stored. Getting these wrong is the single largest source of COBOL run-time failures.

Reading a PICTURE

PIC	Means	Example value
PIC X(10)	10 characters, anything	'SMITH '
PIC 9(5)	5 digits, unsigned	00042
PIC S9(5)	5 digits, signed	-00042
PIC S9(7)V99	7 digits, an implied decimal point, 2 decimals	0001234.56
PIC A(20)	Letters and spaces only	rarely used
PIC 9(3)V9(2)	Same as S9(3)V99 without the sign
PIC ZZZ,ZZ9.99-	An edited field for printing	' 12,345.67-'

USAGE: how it is physically stored

USAGE	Also called	Storage	Use for
DISPLAY	the default	One byte per digit or character	Anything read or written as text
COMP-3	packed decimal	Two digits per byte, sign in the last nibble	Money and counters — the workhorse
COMP / BINARY	binary	2, 4 or 8 bytes	Subscripts, counters, flags
COMP-1 / COMP-2	floating point	4 / 8 bytes	Scientific work; almost never money

The same value, three ways

PIC 9(5) DISPLAY

Value 123455 bytesF1 F2 F3 F4 F5Readable in a dump

PIC S9(5) COMP-3

Value 123453 bytes12 34 5CC = positive sign

PIC S9(5) COMP

Value 123454 bytes00 00 30 39Pure binary

Why COMP-3 is everywhere

Packed decimal stores two digits per byte and keeps exact decimal arithmetic. A PIC S9(7)V99 COMP-3 field holds nine digits in five bytes, computes money exactly, and is the format the hardware has instructions for. It is the default choice for any numeric business field. The cost is that you cannot read it in a dump without decoding it — which is exactly the skill the next lesson needs.

MOVE and the rules that surprise people

What MOVE actually does

* character move: left-justified, padded or truncated on the RIGHT
01 WS-A PIC X(05) VALUE 'ABCDE'.
01 WS-B PIC X(03).
   MOVE WS-A TO WS-B      >> WS-B = 'ABC'   (E and D lost)

* numeric move: aligned on the DECIMAL POINT, padded or truncated at both ends
01 WS-C PIC S9(5)V99 VALUE 12345.67.
01 WS-D PIC S9(3)V9.
   MOVE WS-C TO WS-D      >> WS-D = 345.6  (high-order AND low-order lost)

* the silent one that causes S0C7 later
01 WS-E PIC X(05) VALUE SPACES.
01 WS-F PIC 9(05).
   MOVE WS-E TO WS-F      >> WS-F now contains spaces, not digits
   ADD 1 TO WS-F          >> S0C7

Initialising properly

INITIALIZE sets numeric fields to zero and character fields to spaces, following the field types.
MOVE ZEROES TO a group item moves the *character* zero to every byte — which is not the same as setting a COMP-3 field to zero.
VALUE clauses in WORKING-STORAGE initialise once at program start, not on every call in a subprogram.

Example, line by line

COBOLWhat it means

01 CUSTOMER-RECORD.

Group item: names the whole record. It holds no data of its own, only the fields below it.

05 CUSTOMER-ID PIC 9(8).

Numeric field of 8 digits, stored one digit per byte (zoned decimal).

05 CUSTOMER-NAME PIC X(40).

Character field of 40 bytes, padded with spaces on the right.

05 BALANCE PIC S9(7)V99 COMP-3.

Signed packed decimal: 9 digits, 2 of them after an implied decimal point, in 5 bytes.

05 STATUS-CODE PIC X.

A single character.

88 ACTIVE VALUE 'A'.

Condition name: IF ACTIVE is the same as IF STATUS-CODE = 'A'.

Try it yourself

TRY IT YOURSELF

How many bytes does BALANCE, defined as PIC S9(7)V99 COMP-3, occupy?

Show a hint

Packed decimal stores two digits per byte, and the sign needs half a byte.

Show the solution

5 bytes. 9 digits plus the sign is 10 half-bytes, and two half-bytes fit in each byte.