5.3.12.1 REDEFINES Clause Considerations
Data items within an area can be redefined without changing their lengths. For example:
05 NAME-2.
10 SALARY PICTURE XXX.
10 SO-SEC-NO PICTURE X(9).
10 MONTH PICTURE XX.
05 NAME-1 REDEFINES NAME-2.
10 WAGE PICTURE XXX.
10 EMP-NO PICTURE X(9).
10 YEAR PICTURE XX.
Data item lengths and types can also be re-specified within an area. For
example:
05 NAME-2.
10 SALARY PICTURE XXX.
10 SO-SEC-NO PICTURE X(9).
10 MONTH PICTURE XX.
05 NAME-1 REDEFINES NAME-2.
10 WAGE PICTURE 999V999.
10 EMP-NO PICTURE X(6).
10 YEAR PICTURE XX.
When an area is redefined, all descriptions of the area are always in
effect; that is, redefinition does not cause any data to be erased and
never supersedes a previous description. Thus, if B REDEFINES C has been
specified, either of the two procedural statements, MOVE X TO B and MOVE Y
TO C, could be executed at any point in the program.
In the first case, the area described as B would assume the value and format of X. In the second case, the same physical area (described now as C) would assume the value and format of Y. Note that, if the second statement is executed immediately after the first, the value of Y replaces the value of X in the one storage area.
The usage of a redefining data item need not be the same as that of a redefined item. This does not, however, cause any change in existing data. For example:
05 B PICTURE 99 USAGE DISPLAY VALUE 8.
05 C REDEFINES B PICTURE S99 USAGE COMPUTATIONAL-4.
05 A PICTURE S99 USAGE COMPUTATIONAL-4.
Redefining B does not change the bit configuration of the data in the
storage area. Therefore, the following two statements produce different
results:
ADD B TO A
ADD C TO A
In the first case, the value 8 is added to A (because B has USAGE
DISPLAY). In the second statement, the value -3848 is added to A (because
C has USAGE COMPUTATIONAL-4), and the bit configuration of the storage
area has the binary value -3848.
The above example demonstrates how the improper use of redefinition can give unexpected or incorrect results.
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