XL Fortran Enterprise Edition for AIX : User's Guide - IBM

File Positioning
Note: Because unit 0 is preconnected for standard error, you cannot use it for the
following statements: CLOSE, ENDFILE, BACKSPACE, REWIND, and
direct or stream input/output. You can use it in an OPEN statement only to
change the values of the BLANK=, DELIM=, or PAD= specifiers.
You can also implicitly connect units 5 and 6 (and *) by using I/O statements that
follow a CLOSE:
WRITE (6,10) "This message goes to stdout."
CLOSE (6)
WRITE (6,10) "This message goes in the file fort.6."
PRINT *, "Output to * now also goes in fort.6."
10 FORMAT (A)
END
The FORM= specifier of implicitly connected files has the value FORMATTED
before any READ, WRITE, or PRINT statement is performed on the unit. The first
such statement on such a file determines the FORM= specifier from that point on:
FORMATTED if the formatting of the statement is format-directed, list-directed, or
namelist; and UNFORMATTED if the statement is unformatted.
Preconnected files also have FORM=’FORMATTED’, STATUS=’OLD’, and
ACTION=’READWRITE’ as default specifier values.
The other properties of a preconnected or implicitly connected file are the default
specifier values for the OPEN statement. These files always use sequential access.
If you want XL Fortran to use your own file instead of the fort.n file, you can
either specify your file for that unit through an OPEN statement or create a
symbolic link before running the application. In the following example, there is a
symbolic link between myfile and fort.10:
ln myfile fort.10
When you run an application that uses the preconnected file fort.10 for
input/output, XL Fortran uses the file myfile instead. The file fort.10 exists, but
only as a symbolic link. The following command will remove the symbolic link,
but will not affect the existence of myfile:
rm fort.10
Table 21. Position of the File Pointer When a File Is Opened with No POSITION= Specifier
-qposition suboptions Implicit OPEN Explicit OPEN
File
exists
File
does
not
exist
STATUS =
’NEW’
File
exists
File
does
not
exist
STATUS = ’OLD’ STATUS =
’UNKNOWN’
File
exists
option not specified Start Start Error Start Start
▌1▐, ▌3▐
File
does
not
exist
File
exists
File
does
not
exist
Error Start Start
appendold ▌2▐ Start Start Error Start End Error Start Start
appendunknown Start Start Error Start Start
▌3▐
Error End Start
appendold and appendunknown Start Start Error Start End Error End Start
Implementation Details of XL Fortran Input/Output 327