Open Watcom FORTRAN 77 Language Reference

Language Reference
SUBROUTINE PRINT_ITEM( ITEM )
STRUCTURE /DATA_MAP/
INTEGER TYPE
UNION
MAP
LOGICAL
END MAP
MAP
INTEGER
LGL
INT
END MAP
MAP
REAL
FLT
END MAP
MAP
DOUBLE PRECISION DBL
END MAP
END UNION
END STRUCTURE
RECORD /DATA_MAP/ ITEM
END
IF( ITEM%TYPE .EQ. 1 ) THEN
PRINT ’(L2)’, ITEM%LGL
ELSEIF( ITEM%TYPE .EQ. 2 ) THEN
PRINT ’(I8)’, ITEM%INT
ELSEIF( ITEM%TYPE .EQ. 3 ) THEN
PRINT ’(E12.5)’, ITEM%FLT
ELSEIF( ITEM%TYPE .EQ. 4 ) THEN
PRINT ’(D12.5)’, ITEM%DBL
ENDIF
The organization of the record in memory is as follows:
offset +0 +4 +8
integer logical (slack)
integer
real
(slack)
(slack)
double precision
The first 4 bytes of storage are occupied by TYPE. The next 4 to 8 bytes of storage are occupied by either
LGL, INT, FLT, or DBL depending on the interpretation of the contents of the variable TYPE. The size
of the record ITEM is a total of 12 bytes. Based on the conventions of the above program example, only 8
bytes of the record ITEM are used when TYPE is 1, 2, or 3. When TYPE is 4 then 12 bytes of the record
are used.
The following example maps out a 4-byte integer on an Intel 80x86-based processor.
170 Unions