Open Watcom FORTRAN 77 Language Reference

Language Reference
accessed directly. You have no choice but to write records sequentially. Sometimes a file
that was created using the sequential access method may not be accessed using the direct
method or vice versa. FORTRAN calls this property of a file the "set of allowed access
methods".
Record Form
Some files have the property of being able to handle both formatted and unformatted record
formats. Some files may only have one of these properties. For example, if you tried to
write unformatted records to a line printer, the result might be gibberish. On the other hand
a graphics printer may readily accept unformatted records for reproducing graphical images
on paper. FORTRAN calls this property of a file the "set of allowed forms".
Record Length Another property of a file is record length. Some files may have restrictions on the length
of a record. Some files do not allow records of zero length. Other files, such as printers,
may restrict the length of a record to some maximum. FORTRAN calls this property the
"set of allowed record lengths".
10.4.2 Internal Files
Internal files are special files that reside only in memory. They do not exist before or after the execution of
a FORTRAN program, only during the execution of a program. An internal file allows you to treat
memory in the computer as if it were one or more records in a file. The file must be a character variable,
character array element, character array, or character substring. A record in this file may be a character
variable, character array element or character substring.
Another way of looking at this is that an internal file that is either a character variable, character array
element or character substring can contain only one record but an internal file that is a character array can
contain several records (as many as there are elements in the array).
Properties of Internal Files
Records
Unless the name of a character array is used, only one record is contained in an internal file.
The length of this record is the same as the length of the variable, array element, or
substring. If the file is a character array then each element in the array is a record. The
order of the records in the file is the same as the order of the elements in the array. The
length of a record in this case is the same as the length of the character array elements.
If the number of characters written to a record in an internal file is less than the length of
the record then the record is padded with blanks.
Definition
Position
Restrictions
A record may be read only if the variable, array element, or substring is defined (i.e., it has
been assigned some value). Definition may not only result from an output statement such
as WRITE. It may also be defined through other means; for example, a character
assignment statement.
For all input/output statements, the file is positioned at the beginning of the first record.
Multiple records may be read or written using the "slash" format edit descriptor (see the
chapter entitled "Format" on page 225).
Only sequential access formatted input and output statements ( READ and WRITE) may be
used to transfer data to and from records in an internal file.
218 Files