Fortran 77 Language Reference | ![]() ![]() ![]() ![]() ![]() |
VMS Language Extensions
This chapter describes the VMS language extensions that Sun WorkShop Fortran 77 supports. These extensions are all, of course, nonstandard.
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Background
This FORTRAN compiler includes the VMS extensions to make it as easy as possible to port FORTRAN programs from VMS environments to Solaris environments. The compiler provides almost complete compatibility with VMS FORTRAN. These extensions are included in
dbx
as well asf77
.VMS Language Features in Sun Fortran
This list is a summary of the VMS features that are included in
f77
. Details are elsewhere in this manual.
- Namelist I/O
- Unlabeled
DO
...
END
DO- Indefinite
DO
WHILE
...
END
DOBYTE
data type- Logical operations on integers, and arithmetic operations on logicals
- Additional field and edit descriptors for
FORMAT
statements:- Default field indicators for w, d, and e fields in
FORMAT
statements- Reading into Hollerith edit descriptors
APPEND
option forOPEN
- Long names (32 characters)
_
and$
in names- Long source lines (132-character), if the
-e
option is on- Records, structures, unions, and maps
- Getting addresses by the
%LOC
function- Passing arguments by the
%VAL
function- End-of-line comments
OPTIONS
statement- VMS Tab-format source lines are valid.
- Initialize in common
- You can initialize variables in common blocks outside of
BLOCK
DATA
subprograms. You can initialize portions of common blocks, but you cannot initialize portions of one common block in more than one subprogram.- Radix-50
- Radix-50 constants are implemented as
f77
bit-string constants, that is, no type is assumed.IMPLICIT
NONE
is treated asIMPLICIT
UNDEFINED
(A-Z)VIRTUAL
is treated asDIMENSION
.- Initialize in declarations
- Initialization of variables in declaration statements is allowed. Example:
CHARACTER*10 NAME /'Nell'/- Noncharacter format specifiers
- If a runtime format specifier is not of type
CHARACTER
, the compiler accepts that too, even though the FORTRAN Standard requires theCHARACTER
type.- Omitted arguments in subprogram calls
- The compiler accepts omitted actual argument in a subroutine call, that is, two consecutive commas compile to a null pointer. Reference to that dummy argument gives a segmentation fault.
REAL*16
- (SPARC only) The compiler treats variables of type
REAL*16
as quadruple precision.- Noncharacter variables
- The FORTRAN Standard requires the
FILE=
specifier forOPEN
andINQUIRE
to be an expression of typeCHARACTER
.f77
accepts a numeric variable or array element reference.- Consecutive operators
f77
allows two consecutive arithmetic operators when the second operator is a unary+
or-
. Here are two consecutive operators:
X = A ** -B- The above statement is treated as follows:
X = A ** (-B)- Illegal real expressions
- When the compiler finds a
REAL
expression where it expects an integer expression, it truncates and makes a type conversion toINTEGER
.- Examples: Contexts for illegal real expressions that
f77
converts to integer:
- Alternate
RETURN
- Dimension declarators and array subscripts
- Substring selectors
- Computed
GO
TO
- Logical unit number, record number, and record length
- Typeless numeric constants
- Binary, hexadecimal and octal constants are accepted in VMS form.
- Example: Constants-Binary (
B
), Octal (O
), Hexadecimal (X
orZ
):
DATA N1 /B'0011111'/, N2/O'37'/, N3/X'1f'/, N4/Z'1f'/- Function length on function name, rather than on the word
FUNCTION
- The compiler accepts nonstandard length specifiers in function declarations.
- Example: Size on function name, rather than on the word
FUNCTION
:
INTEGER FUNCTION FCN*2 ( A, B, C )
TYPE
andACCEPT
statements are allowed.- Alternate return
- The nonstandard
&
syntax for alternate-return actual arguments is treated as the standard FORTRAN*
syntax. Example
:
CALL SUBX ( I, *100, Z)
! StandardCALL SUBX ( I, &100, Z ) ! Nonstandard alternate syntax- The
ENCODE
andDECODE
statements are accepted.- Direct I/O with
'N
record specifier
- The nonstandard record specifier
'N
for direct-access I/O statements is accepted.- Example: A nonstandard form for record specifier:
READ ( K ' N ) LIST- The above is treated as:
READ ( UNIT=K, REC=N ) LIST- The logical unit number is
K
and the number of the record isN
.NAME
,RECORDSIZE
, andTYPE
options--OPEN
has the following alternative options:DISPOSE=
p
- The
DISPOSE=
p clause in theCLOSE
statement is treated asSTATUS=
p.- Special Intrinsics
- The compiler processes certain special intrinsic functions:
%VAL
is accepted
%LOC
is treated asLOC
%REF(
expr)
is treated as expr (with a warning if exprisCHARACTER
)
%DESCR
is reported as an untranslatable feature- Variable Expressions in
FORMAT
Statements
- In general, inside a
FORMAT
statement, any integer constant can be replaced by an arbitrary expression; the single exception is the n in an nH...
edit descriptor. The expression itself must be enclosed in angle brackets.
- Example: The
6
in the following statement is a constant:
1 FORMAT( 3F6.1 )6
can be replaced by the variableN
, as in:
1 FORMAT( 3F<N>.1 )VMS Features Requiring
-xl
or-vax=
specYou get most VMS features automatically without any special options. For a few of them, however, you must add the
-xl
option on thef77
command line.In general, you need this
-xl
option if a source statement can be interpreted for either a VMS way of behavior or anf77
way of behavior, and you want the VMS way of behavior. The-xl
option forces the compiler to interpret it as VMS FORTRAN.Note also the
-vax=
spec option, which allows specification of these VMS extensions individually. See the Fortran User's Guide for details.Summary of Features That Require
-xl[d]
You must use
-xl[d]
to access the following features:
- Unformatted record
size
in words rather than bytes (-xl
)- VMS-style logical file names (
-xl
)- Quote (
"
) character introducing octal constants (-xl
)- Backslash (
\
) as ordinary character within character constants (-xl
)- Nonstandard form of the
PARAMETER
statement (-xl
)- Debugging lines as comment lines or FORTRAN statements (
-xld
)- Align structures as in VMS FORTRAN (
-xl
)Details of Features That Require
-xl[d]
- Unformatted record
size
in words rather than bytes
- In
f77
, direct-access, unformatted files are always opened with the logical record size in bytes.- If the
-xl[d]
option is not set, then the argument n in theOPEN
optionRECL=
n is assumed to be the number of bytes to use for the record size.- If the
-xl[d]
option is set, then the argument n in theOPEN
optionRECL=
n is assumed to be the number of words, so the compiler uses n*4
as the number of bytes for the record size.- If the
-xl[d]
option is set, and if the compiler cannot determine if the file is formatted or unformatted, then it issues a warning message that the record size may need to be adjusted. This result could happen if the information is passed in variable character strings.- The record size returned by an
INQUIRE
statement is not adjusted by the compiler; that is,INQUIRE
always returns the number of bytes.- These record sizes apply to direct-access, unformatted files only.
- VMS-style logical file names
- If the
-xl[d]
option is set, then the compiler interprets VMS logical file names on theINCLUDE
statement if it finds the environment variable,LOGICALNAMEMAPPING
, to define the mapping between the logical names and the UNIX path name.- You set the environment variable to a string of the form:
"lname1=path1; lname2=path2; ... " - Remember these rules for VMS style logical file names:
- Each lname is a logical name and each path1, path2, and so forth, is the path name of a directory (without a trailing
/
).- It ignores all blanks when parsing this string.
- It strips any trailing
/[no]list
from the file name in theINCLUDE
statement.- Logical names in a file name are delimited by the first
:
in the VMS file name.- It converts file names from lname1:file to the path1/file form.
- For logical names, uppercase and lowercase are significant. If a logical name is encountered on the
INCLUDE
statement which is not specified in theLOGICALNAMEMAPPING
, the file name is used, unchanged.- Quote (
"
) character introducing octal constants
- If the
-xl[d]
compiler option is on, a VMS FORTRAN octal integer constant is treated as its decimal form.- Example: VMS octal integer constant:
JCOUNT = ICOUNT + "703- The above statement is treated as:
JCOUNT = ICOUNT + 451- If the
-xl[d]
option is not on, then the"703
is an error.- With
-xl[d]
, the VMS FORTRAN notation"703
signalsf77
to convert from the integer octal constant to its integer decimal equivalent, 451 in this case. In VMS FORTRAN,"703
cannot be the start of a character constant, because VMS FORTRAN character constants are delimited by apostrophes, not quotes.- Backslash (
\
) as ordinary character within character constants
- If the
-xl[d]
option is on, a backslash in a character string is treated as an ordinary character; otherwise, it is treated as an escape character.- Nonstandard form of the
PARAMETER
statement
- The alternate
PARAMETER
statement syntax is allowed, if the-xl[d]
option is on.- Example: VMS alternate form of
PARAMETER
statement omits the parentheses:
PARAMETER FLAG1 = .TRUE.- Debugging lines as comment lines or FORTRAN statements (
-xld
)
- The compiler interprets debugging lines as comment lines or FORTRAN statements, depending on whether the
-xld
option is set. If set, they are compiled; otherwise, they are treated as comments.- Example: Debugging lines:
REAL A(5) / 5.0, 6.0, 7.0, 8.0, 9.0 /DO I = 1, 5X = A(I)**2D PRINT *, I, XEND DOPRINT *, 'done'END- With
-xld
, this code printsI
andX
. Without-xld
, it does not print them.- Align structures as in VMS FORTRAN
- Use this feature if your program has some detailed knowledge of how VMS structures are implemented. If you need to share structures with C, you should use the default: no
-xl
Unsupported VMS FORTRAN
Most VMS FORTRAN extensions are incorporated into the
f77
compiler. The compiler writes messages to standard error for any unsupported statements in the source file. The following is a list of the few VMS statements that are not supported.
DEFINE
FILE
statementDELETE
statementUNLOCK
statementFIND
statementREWRITE
statementKEYID
and key specifiers inREAD
statements- Nonstandard
INQUIRE
specifiers- Nonstandard
OPEN
specifiers
ASSOCIATEVARIABLE
BLOCKSIZE
BUFFERCOUNT
CARRIAGECONTROL
DEFAULTFILE
DISP[OSE]
EXTENDSIZE
INITIALSIZE
KEY
MAXREC
NOSPANBLOCKS
ORGANIZATION
RECORDTYPE
SHARED
USEROPEN
- The intrinsic function,
%DESCR
- The following parameters on the
OPTIONS
statement:- Some of the
INCLUDE
statement
- Some aspects of the
INCLUDE
statement are converted. TheINCLUDE
statement is operating system-dependent, so it cannot be completely converted automatically. The VMS version allows a module-name and aLIST
control directive that are indistinguishable from a continuation of a UNIX file name. Also, VMS ignores alphabetic case, so if you are inconsistent about capitalization, distinctions are made where none are intended.- Getting a long integer--expecting a short
- In VMS FORTRAN, you can pass a long integer argument to a subroutine that expects a short integer. This feature works if the long integer fits in 16 bits, because the VAX addresses an integer by its low-order byte. This feature does not work on SPARC systems.
- Those VMS system calls that are directly tied to that operating system
- Initializing a common block in more than one subprogram
- Alphabetizing common blocks so you can rely or depend on the order in which blocks are loaded. You can specify the older with the
-M
mapfile option told
.- If you use the defaults for both of the following:
- then formatted numeric input ignores imbedded and trailing blanks. The corresponding VMS defaults treat them as zeros.
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