Open Watcom FORTRAN 77 Language Reference

Language Reference
Example:
WRITE(1,*) ’Output on unit 1’
END
Open Watcom FORTRAN 77 constructs a file name using the specified unit number. The format of the file
name is described in the User’s Guide since it varies from one computer system to the next.
Connection of a unit to a file does not imply that the file must exist. For example, it could be a new file.
When we speak of a unit being connected to a file, we can also say that a file is connected to a unit. Under
the rules of FORTRAN, it is illegal to connect the same file to more than one unit at the same time.
However, a file may be connected to different units at different times. We shall explain how this is
possible.
A file may be disconnected from a unit by the use of the CLOSE statement.
Example:
CLOSE(UNIT=1)
Under certain circumstances, the file may be disconnected from a unit by the use of the OPEN statement.
Example:
OPEN(UNIT=1,FILE=’FILE1’)
.
.
.
OPEN(UNIT=1,FILE=’FILE2’)
In the above example, the second OPEN statement disconnects unit 1 from one file and connects it to a
second file. You may think of the second OPEN statement as automatically closing the first file and then
establishing a connection to the second file.
If a unit has been disconnected from a file through the execution of a CLOSE statement, the unit may
subsequently be connected to the same file or to a different file. It also follows that a file which has been
disconnected from one unit number may be connected to the same unit number or a different unit number.
The following example may help to illustrate this last point.
Example:
OPEN(UNIT=1,FILE=’FILE1’)
.
.
.
CLOSE(UNIT=1)
OPEN(UNIT=2,FILE=’FILE1’)
Once a file has been disconnected, the only means for referring to the file is by its name in an OPEN
statement or an INQUIRE statement.
220 Units