Open Watcom FORTRAN 77 Language Reference

Input/Output
Although FORTRAN 77 states that list-directed formatted input/output to an internal file is
not permitted, Open Watcom FORTRAN 77 allows you to use list-directed formatted
input/output statements. This is an extension to the language standard.
Example:
WRITE(INTFIL,*) X, Y, Z
No other input/output statements ( OPEN, ENDFILE, REWIND, etc.) may be used.
Internal files may be used to convert data from one format to another. The following example illustrates
one use of internal files.
Example:
CHARACTER*11 INPUT
PRINT *, ’TYPE IN ’’I’’ FOLLOWED BY AN INTEGER’
PRINT *, ’OR TYPE IN ’’R’’ FOLLOWED BY A REAL’
READ 100, INPUT
100 FORMAT( A11 )
IF( INPUT(1:1) .EQ. ’I’ )THEN
READ( UNIT=INPUT(2:11), FMT=’(I10)’ ) IVAR
PRINT *, ’AN INTEGER WAS ENTERED ’, IVAR
ELSE IF( INPUT(1:1) .EQ. ’R’ )THEN
READ( UNIT=INPUT(2:11), FMT=’(F10.3)’ ) RVAR
PRINT *, ’A REAL NUMBER WAS ENTERED ’, RVAR
END IF
END
After checking for an "I" or "R" as the first character of the character variable INPUT, the appropriate
internal READ statement is executed.
10.5 Units
Many FORTRAN 77 input/output statements refer to external files using a mechanism called the unit.
There are many units available to the FORTRAN 77 programmer. Open Watcom FORTRAN 77 numbers
these units from 0 to 999; thus the unit number is a non-negative integer less than 1000.
A unit may be associated with a particular file. This association is called connection. Any unit may or may
not be connected to a file. There are a number of ways in which this connection may be established.
A unit may be preconnected to a file before execution of a program begins. The User’s Guide describes the
mechanism for preconnecting a unit to a file.
Alternatively, a unit may become connected to a file by the execution of an OPEN statement.
All input/output statements except OPEN, CLOSE, and INQUIRE must refer to a unit that is connected to
a file. Open Watcom FORTRAN 77 automatically establishes a connection of the unit to a file if no
connection previously existed. Consider the following example in which unit number 1 is not previously
connected to a file.
Units 219