VMS Help
FORTRAN, Compatibility Features
*Conan The Librarian (sorry for the slow response - running on an old VAX)
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Compaq Fortran provides the following language features to aid
compatibility with other versions of Fortran:
o The DEFINE FILE, ENCODE, DECODE, and FIND statements
o A NOF77 interpretation of the EXTERNAL statement
o Octal forms of integer constants
o An alternative syntax for the PARAMETER statement
o The VIRTUAL statement
o An alternative syntax for bit constants
o An alternative syntax for a record specifier
These language features are particularly useful in transporting
older Fortran programs to a VAX system. However, you should avoid
using them in new programs on these systems, and in new programs
for which portability to other FORTRAN-77 implementations is
important.
The DEFINE FILE statement establishes the size and structure of
files with relative organization and associates them with a logical
unit number. The DEFINE FILE statement is comparable to the OPEN
statement (in situations where you can use the OPEN statement, it
is the preferable mechanism for creating and opening files).
Statement format:
DEFINE FILE u(m, n, U, asv) [,u(m, n, U, asv)]...
u Is an integer constant or variable that specifies the
logical unit number.
m Is an integer constant or variable that specifies the
number of records in the file.
n Is an integer constant or variable that specifies the
length of each record in 16-bit words (2 bytes).
U Specifies that the file is unformatted (binary); this
is the only acceptable entry in this position.
asv Is an integer variable, called the associated variable
of the file. At the end of each direct access I/O
operation, the record number of the next higher numbered
record in the file is assigned to "asv"; "asv" must not
be a dummy argument.
The DEFINE FILE statement specifies that a file containing "m"
fixed-length records, each composed of n 16-bit words, exists (or
is to exist) on the specified logical unit. The records in the
file are numbered sequentially from 1 through "m".
A DEFINE FILE statement must be executed before the first direct
access I/O statement referring to the specified file, even though
the DEFINE FILE statement does not itself open the file. The file
is actually opened when the first direct access I/O statement for
the unit is executed.
If this I/O statement is a WRITE statement, a new relative
organization file is created. If it is a READ or FIND statement,
an existing file is opened, unless the specified file does not
exist. If a file does not exist, an error occurs.
The ENCODE and DECODE statements transfer data between variables or
arrays in internal storage. The ENCODE statement translates data
from internal (binary) form to character form. Inversely, the
DECODE statement translates data from character to internal form.
These statements are comparable to using internal files in
formatted sequential WRITE and READ statements, respectively.
Statement format:
ENCODE (c,f,b [,IOSTAT=ios] [,ERR=s]) [list]
DECODE (c,f,b [,IOSTAT=ios] [,ERR=s]) [list]
c Is an integer expression. In the ENCODE statement,
"c" is the number of characters (in bytes) to be
translated to character form. In the DECODE statement,
"c" is the number of characters to be translated to
internal form.
f Is a format identifier. An error occurs if more than
one record is specified.
b Is a scalar or array reference. If b is an array
reference, its elements are processed in the
order of subscript progression. The data type of "b"
determines the number of characters that ENCODE or
DECODE can process.
In the ENCODE statement, "b" receives the characters
after translation to external form. If less than "c"
characters are received, the remaining character
positions are filled with blank characters.
In the DECODE statement, "b" contains the characters
to be translated to internal form.
ios Is an integer scalar memory reference that is defined
as a positive integer if an error occurs, and zero
if no error occurs.
s Is the label of an executable statement.
list Is an I/O list.
In the ENCODE statement, the "list" contains the data
to be translated to character form. In the DECODE
statement, the "list" receives the data after
translation to internal form.
The interaction between the format specifier and the
I/O list is the same as for a formatted I/O statement.
The FIND statement positions a direct access file at a particular
record and sets the associated variable of the file to that record
number. It is comparable to a direct access READ statement with no
I/O list, and can open an existing file. No data transfer takes
place. Statement format:
FIND (u'r [,ERR=s] [,IOSTAT=ios])
FIND ([UNIT=]u, REC=r [,ERR=s] [,IOSTAT=ios])
u Is a logical unit number. It must refer to a
relative organization file.
r Is the direct access record number. It cannot
be less than one or greater than the number of
records defined for the file.
s Is the label of the executable statement that
receives control if an error occurs.
ios Is an integer variable or integer array element
that is defined as a positive integer if an error
occurs, and as a zero if no error occurs.
If you specify the /NOF77 qualifier, you get an interpretation of
the EXTERNAL statement that aids compatibility with older versions
of Fortran. (The ANSI FORTRAN-77 interpretation is incompatible
with the previous standard and previous Compaq implementations.)
The NOF77 interpretation combines the functionality of the
INTRINSIC statement with that of the EXTERNAL statement discussed
under the Help topic: Statements EXTERNAL.
The NOF77 EXTERNAL statement lets you use subprograms as arguments
to other subprograms. The subprograms to be used as arguments can
be either user-supplied procedures or Fortran library functions.
Statement format:
EXTERNAL [*]v [,[*]v]...
v Is the symbolic name of a subprogram or the name of
a dummy argument associated with the symbolic name
of a subprogram.
* Specifies that a user-supplied function is to be used
instead of a Fortran library function having the same
name.
The NOF77 EXTERNAL statement declares that each symbolic name in
its list is an external procedure name. Such a name can then be
used as an actual argument to a subprogram, which in turn can use
the corresponding dummy argument in a function reference or CALL
statement.
However, used as an argument, a complete function reference
represents a value, not a subprogram name.
Octal forms of integer constants allow compatibility with PDP-11
FORTRAN. Statement format:
"nn
nn Is a string of digits in the range 0 to 7 (for
example "107).
Integer constants in octal form have integer data type and are
treated as integers.
This statement is similar to the one discussed in Help topic:
Statements PARAMETER; they both assign a symbolic name to a
constant. However, this PARAMETER statement differs from the other
one in the following two ways: its list is not bounded with
parentheses; and the form of the constant, rather than implicit or
explicit typing of the symbolic name, determines the data type of
the variable. Statement format:
PARAMETER p=c [,p=c]...
p Is a symbolic name.
c Is a constant, the symbolic name of a constant, or a
compile-time constant expression.
The VIRTUAL statement is included for compatibility with PDP-11
FORTRAN. It has the same form and effect as the DIMENSION
statement (see Help Topic: Statements DIMENSION).
In Compaq Fortran, you can use the following alternative syntax for
binary, octal, and hexadecimal constants:
Alternative Syntax Equivalent
------------------ ----------
Binary B'0..1' '0..1'B
Octal O'0..7' '0..7'O
Hexadecimal X'0..F' or Z'0..F' '0..F'X or '0..F'Z
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9 - Record Specifier Syntax
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In Compaq Fortran, you can specify the following form for a record
specifier:
'r
r Is a numeric expression with a value that represents
the position of the record to be accessed using direct
access I/O. The value must be greater than or equal to 1,
and less than or equal to the maximum number of records
allowed in the file. If necessary, a record number is
converted to integer data type before being used.
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