This section provides compatibility information for those porting Compaq Fortran 77 applications from Compaq Tru64 UNIX systems. It discusses the following topics:

• Major language features for compatibility with Compaq Fortran 77 for Compaq Tru64 UNIX systems ( Section A.2.1)
• Language differences between Compaq Fortran and Compaq Fortran 77, including Compaq Fortran 77 extensions on Compaq Tru64 UNIX Systems that are not supported by this version of Compaq Fortran on Compaq Tru64 UNIX Systems ( Section A.2.2)
• Language features detected during compilation differently by Compaq Fortran than Compaq Fortran 77 for Compaq Tru64 UNIX Systems ( Section A.2.3)

On Compaq Tru64 UNIX systems, to simplify porting applications from Compaq Fortran 77 to Compaq Fortran, Compaq Fortran Version 5.3 supports the following Compaq Fortran 77 extensions that are not part of the Fortran 95/90 standards:

• Record structures (STRUCTURE and RECORD statements)
• I/O statements, including PRINT, ACCEPT, TYPE, DELETE, and UNLOCK
• I/O statement specifiers, such as the INQUIRE statement specifiers CARRIAGECONTROL, CONVERT, ORGANIZATION, and RECORDTYPE
• Certain data types, including 8-byte INTEGER and LOGICAL variables and 16-byte REAL variables (available on Alpha systems)
• Size specifiers for data declaration statements, such as INTEGER*4, in addition to the KIND type parameter
• IEEE floating-point data type in memory
• The POINTER statement and its associated data type (CRAY pointers).
• The typeless PARAMETER statement
• The VOLATILE statement
• The AUTOMATIC and STATIC statements
• Built-in functions used in argument lists, such as %VAL and %LOC
• Hollerith constants
• Variable-format expressions (VFEs)
• Certain intrinsic functions
• The tab source form (resembles fixed-source form)
• I/O formatting descriptors
• USEROPEN routines for user-defined open routines
• Additional language features, including the DEFINE FILE, ENCODE, DECODE, and VIRTUAL statements

In addition to language extensions, Compaq Fortran Version 5.3 also supports the following Compaq Fortran 77 features:

• Compaq Fortran 77 compilation control statements and directives (see the Compaq Fortran Language Reference Manual), including:
  • INCLUDE statement forms using /LIST and /NOLIST (requires compiling with -vms )
  • OPTIONS statement to override or set compiler command-line options
  • General cDEC$ directives, including:

    cDEC$ ALIAS
    cDEC$ IDENT
    cDEC$ OPTIONS
    cDEC$ PSECT
    cDEC$ TITLE
    cDEC$ SUBTITLE

• A nearly identical set of command-line options and their associated features (see Section A.2.4).
• The ability to call between Compaq Fortran 77 and Compaq Fortran routines and a common run-time environment. For example, a Compaq Fortran 77 procedure and a Compaq Fortran procedure can perform I/O to the same unit number (see Section 11.3).
• foriosdef.for symbolic parameter definitions for use with run-time (IOSTAT) error handling (see Chapter 8).

For More Information:

On the Compaq Fortran language, see the Compaq Fortran Language Reference Manual.

A.2.2 Language Features Provided Only by Compaq Fortran 77 for Compaq Tru64 UNIX Systems

This section lists Compaq Fortran 77 extensions to the FORTRAN-77 standard that are not included in Compaq Fortran Version 5.3 for Compaq Tru64 UNIX Systems. Where appropriate, this list indicates equivalent Compaq Fortran language features.

Compaq Fortran conforms to the Fortran 95/90 standard, which is a superset of the FORTRAN-77 standard. Compaq Fortran provides many but not all of the FORTRAN-77 extensions provided by Compaq Fortran 77.

The following FORTRAN-77 extensions provided by Compaq Fortran 77 on Compaq Tru64 UNIX systems are not provided by Compaq Fortran in Version 5.3:

• Octal notation for integer constants is not part of the Compaq Fortran Language. Compaq Fortran 77 ( f77 command) only supports this feature when the -vms option is specified. For example:

  I = "0014 ! Assigns 12 to I, not supported by Compaq Fortran

• The Compaq Fortran compiler discards leading zeros for "disp" in the STOP statement. For example:

  STOP 001 ! Prints 1 instead of 001

• When a single-precision constant is assigned to a double-precision variable, Compaq Fortran 77 evaluates the constant in double precision. The Fortran 95/90 standards require that the constant be evaluated in single precision.
  When a single-precision constant is assigned to a double-precision variable with Compaq Fortran, it is evaluated in single precision. You can, however, specify the f90 -fpconstant option to request that a single-precision constant assigned to a double-precision variable be evaluated in double precision.
  In the example below, Compaq Fortran 77 assigns identical values to D1 and D2, whereas Compaq Fortran obeys the standard and assigns a less precise value to D1.
  For example:

  REAL*8 D1,D2 DATA D1 /2.71828182846182/ ! Incorrect - only REAL*4 value DATA D2 /2.71828182846182D0/ ! Correct - REAL*8 value

• The names of intrinsics introduced by Compaq Fortran may conflict with the names of existing external procedures if the procedures were not specified in an EXTERNAL declaration. For example:

  EXTERNAL SUM REAL A(10),B(10) S = SUM(A) ! Correct - invokes external function T = DOT_PRODUCT(A,B) ! Incorrect - invokes intrinsic function

• When writing namelist external records, Compaq Fortran uses the syntax for namelist external records specified by the Fortran 95/90 standards, rather than the Compaq Fortran 77 syntax (an extension to the FORTRAN-77 and Fortran 95/90 standards).
  Consider the following program:

  % cat test.f INTEGER I NAMELIST /N/ I I = 5 PRINT N END

  
  When this program is compiled by the f90 command and run, the following output appears:

  % f90 test.f % a.out &N I = 5 /

  
  When this program is compiled by the f77 command and run, the following output appears:

  % f77 test.f % a.out $N I = 5 $END

  
  Use the -f77rtl option to tell Compaq Fortran to generate NAMELIST output in Compaq Fortran 77 format.
  Compaq Fortran accepts Fortran 95/90 namelist syntax and Compaq Fortran 77 namelist syntax for reading records.

• The Compaq Fortran language does not include C-style escape sequences. For example:

  CHARACTER NL NL = '\n' ! Incorrect NL = CHAR(10) ! Correct

• Compaq Fortran inserts a leading blank when doing list-directed I/O to an internal file. For example:

  CHARACTER*10 C WRITE(C,*) 'FOO' ! C = ' FOO'

• Compaq Fortran 77 and Compaq Fortran produce different output a real value whose data magnitude is 0 with a G field descriptor. For example:

  X = 0.0 WRITE(*,100) X ! Compaq Fortran 77 prints 0.0000E+00 100 FORMAT(G12.4) ! Compaq Fortran prints 0.000

• Compaq Fortran does not allow certain intrinsics (such as SQRT) in constant expressions for array bounds. For example:

  REAL A(SQRT(31.5)) END

• Compaq Fortran 77 returns UNKNOWN while Compaq Fortran returns UNDEFINED when the ACCESS, BLANK, and FORM characteristics can not be determined. For example:

  INQUIRE(20,ACCESS=acc,BLANK=blk,FORM=form)

• Compaq Fortran does not allow an extraneous parenthesis in I/O lists. For example:

  write(*,*) ((i,i=1,1),(j,j=1,2))

• Compaq Fortran does not allow control characters within quoted strings. For example, the assignment statement in the following program is incorrect because it contains the character Ctrl/C.

  character*5 c c = 'ab^cef' end

• Compaq Fortran does not recognize certain hexadecimal and octal constants in DATA statements, such as those used in the following program:

  INTEGER I, J DATA I/O20101/, J/Z20/ TYPE *, I, J END

• Compaq Fortran, like Compaq Fortran 77, supports the use of character literal constants (such as 'ABC' or "ABC") in numeric contexts, where they are treated as Hollerith constants.
  Compaq Fortran 77 also allows character PARAMETER constants (typed and untyped) and character constant expressions (using the // operator) in numeric constants as an undocumented extension.
  Compaq Fortran does allow character PARAMETER constants in numeric contexts, but does not allow character expressions. For example, the following is valid for Compaq Fortran 77, but will result in an error message from Compaq Fortran:

  REAL*8 R R = 'abc' // 'def' WRITE (5,*) R END

  
  Compaq Fortran does allow PARAMETER constants:

  PARAMETER abcdef = 'abc' // 'def' REAL*8 R R = abcdef WRITE (5,*) R END

• Compaq Fortran 77 namelist output formats character data delimited with apostrophes. For example, consider:

  CHARACTER CHAR4*4 NAMELIST /CN100/ CHAR4 CHAR4 = 'ABCD' WRITE(20,CN100) CLOSE (20)

  
  This produces the following output file:

  $CN100 CHAR4 = 'ABCD' $END

  
  This file is read by:

  READ (20, CN100)

  
  In contrast, Compaq Fortran produces the following output file by default:

  &CN100 CHAR4 = ABCD /

  
  When read, this generates a syntax error in NAMELIST input error. To produce delimited strings from namelist output that can be read by namelist input, use DELIM="'" in the OPEN statement of a Compaq Fortran program.

For More Information:

• On argument passing between Compaq Fortran and Compaq Fortran 77 for Compaq Tru64 UNIX systems, see Section 11.3.
• On compatibility between Compaq Fortran for Compaq Tru64 UNIX or Linux Alpha systems and Compaq Fortran on OpenVMS systems, see Section A.4.
• About the Compaq Fortran language, see the Compaq Fortran Language Reference Manual.

The following language features are detected or interpreted differently by Compaq Fortran Version 5.3 and Compaq Fortran 77:

• The Compaq Fortran compiler enforces the constraint that a function cannot be the target of a CALL statement. For example:

  REAL X CALL X() ! Incorrect CALL Y() ! Correct

• The Compaq Fortran compiler enforces the constraint that the "nlist" in an EQUIVALENCE statement must contain at least two variables. For example:

  EQUIVALENCE (X) ! Incorrect EQUIVALENCE (Y,Z) ! Correct

• The Compaq Fortran compiler enforces the constraint that entry points in a SUBROUTINE must not be typed. For example:

  SUBROUTINE ABCXYZ(I) REAL ABC I = I + 1 RETURN ENTRY ABC ! Incorrect BAR = I + 1 RETURN ENTRY XYZ ! Correct I = I + 2 RETURN END SUBROUTINE

• The Compaq Fortran compiler enforces the constraint that a type must appear before each list in an IMPLICIT statement. For example:

  IMPLICIT REAL (A-C), (D-H) ! Incorrect IMPLICIT REAL (O-S), REAL (T-Z) ! Correct

• The Compaq Fortran language disallows passing mismatched actual arguments to intrinsics with corresponding integer formal arguments. For example:

  R = REAL(.TRUE.) ! Incorrect R = REAL(1) ! Correct

• The Compaq Fortran compiler enforces the constraint that a simple list element in an I/O list must be a variable or an expression. For example:

  READ (10,100) (I,J,K) ! Incorrect READ (10,100) I,J,K ! Correct

• The Compaq Fortran compiler enforces the constraint that if two operators are consecutive, the second operator must be a plus or a minus. For example:

  I = J -.NOT.K ! Incorrect I = J - (.NOT.K) ! Correct

• The Compaq Fortran compiler enforces the constraint that character entities with a length greater than 1 cannot be initialized with a bit constant in a DATA statement. For example:

  CHARACTER*1 C1 CHARACTER*4 C4 DATA C1/'FF'X/ ! Correct DATA C4/'FFFFFFFF'X/ ! Incorrect

• The Compaq Fortran compiler enforces the requirement that edit descriptors in the FORMAT statement must be followed by a comma or slash separator. For example:

  1 FORMAT (SSF4.1) ! Incorrect 2 FORMAT (SS,F4.1) ! Correct

• The Compaq Fortran compiler enforces the constraint that the number and types of actual and formal statement function arguments must match (such as incorrect number of arguments). For example:

  CHARACTER*4 C,C4,FUNC FUNC()=C4 C=FUNC(1) ! Incorrect C=FUNC() ! Correct

• The Compaq Fortran compiler detects the use of a format of the form Ew.dE0 at compile time. For example:

  1 format(e16.8e0) ! Compaq Fortran detects error at compile time write(*,1) 5.0 ! Compaq Fortran 77 compiles but an output ! conversion error occurs at run time

• Compaq Fortran detects passing of a statement function to a routine. For example:

  foo(x) = x * 2 call bar(foo) end

• The Compaq Fortran compiler enforces the constraint that a branch to a statement shared by more than one DO statements must occur from within the innermost loop. For example:

  DO 10 I = 1,10 IF (L1) GO TO 10 ! Incorrect DO 10 J = 1,10 IF (L2) GO TO 10 ! Correct 10 CONTINUE

• The Compaq Fortran compiler enforces the constraint that a file must contain at least one program unit. For example, a source file containing only comment lines results in an error at the last line (end-of-file).
  The Compaq Fortran 77 compiler compiles files containing less than one program unit.
• The Compaq Fortran compiler correctly detects misspellings of the ASSOCIATEVARIABLE keyword to the OPEN statement. For example:

  OPEN(1,ASSOCIATEVARIABLE = I) ! Correct OPEN(2,ASSOCIATEDVARIABLE = J) ! Incorrect (extra D)

• The Compaq Fortran language enforces the constraint that the result of an operation is determined by the data types of its operands. For example:

  INTEGER*8 I8 I8 = 2147483647 + 1 ! Incorrect. Produces less accurate ! INTEGER*4 result I8 = 2147483647_8 + 1_8 ! Correct

• The Compaq Fortran compiler enforces the constraint that an object can be typed only once. Compaq Fortran 77 issues a warning message and uses the first type. For example:

  LOGICAL B,B ! Incorrect (B multiply declared)

• The Compaq Fortran compiler enforces the constraint that certain intrinsic procedures defined by the Fortran 95/90 standards cannot be passed as actual arguments. For example, Compaq Fortran 77 allows most intrinsic procedures to be passed as actual arguments, but the Compaq Fortran compiler only allows those defined by the Fortran 95/90 standards (issues an error message).
  Consider the following program:

  program tstifx intrinsic ifix,int,sin call a(ifix) call a(int) call a(sin) stop end subroutine a(f) external f integer f print *, f(4.9) return end

  
  The IFIX and INT intrinsic procedures cannot be passed as actual arguments (the compiler issues an error message). However, the SIN intrinsic is allowed to be passed as an actual argument by the Fortran 95/90 standards.

• Compaq Fortran reports character truncation with an error-level message, not as a warning.
  The following program produces an error message during compilation with Compaq Fortran, whereas Compaq Fortran 77 produces a warning message.

  INIT5 = 'ABCDE' INIT4 = 'ABCD' INITLONG = 'ABCDEFGHIJKLMNOP' PRINT 10, INIT5, INIT4, INITLONG 10 FORMAT (' ALL 3 VALUES SHOULD BE THE SAME: ' 3I) END

• If your code invokes Compaq Fortran intrinsic procedures with the wrong number of arguments or an incorrect argument type, Compaq Fortran reports this with an error-level message, not with a warning. Possible causes include:
  • A Compaq Fortran intrinsic has been added with the same name as a user-defined subprogram and the user-defined subprogram needs to be declared as EXTERNAL.
  • An intrinsic that is an extension to an older Fortran standard is incompatible with a newer standard-conforming intrinsic (for example, the older RAN function that accepted two arguments).
  
  The following program produces an error message during compilation with Compaq Fortran, whereas Compaq Fortran 77 produces a warning message.

  INTEGER ANOTHERCOUNT ICOUNT=0 100 write(6,105) (ANOTHERCOUNT(ICOUNT), INT1=1,10) 105 FORMAT(' correct if print integer values 1 through 10' /10I7) Q = 1. R = .23 S = SIN(Q,R) WRITE (6,110) S 110 FORMAT(' CORRECT = 1.23 RESULT = ',f8.2) END ! INTEGER FUNCTION ANOTHERCOUNT(ICOUNT) ICOUNT=ICOUNT+1 ANOTHERCOUNT=ICOUNT RETURN END REAL FUNCTION SIN(FIRST, SECOND) SIN = FIRST + SECOND RETURN END

• Compaq Fortran reports missing commas in FORMAT descriptors with an error-level message, not as a warning.
  The following program produces an error message during compilation with Compaq Fortran, whereas Compaq Fortran 77 produces a warning message:

  LOGICAL LOG/111/ TYPE 1,LOG 1 FORMAT(' '23X,'LOG='O12) END

  
  In the preceding example, the correct coding (adding the missing comma) for the FORMAT statement is:

  1 FORMAT(' ',23X,'LOG='O12)

• Compaq Fortran generates an error when it encounters a 1-character source line containing a Ctrl/Z character, whereas Compaq Fortran 77 allows such a line (which is treated as a blank line).
• Compaq Fortran does not detect an extra comma in an I/O statement when the -std option is specified, whereas Compaq Fortran 77 with the -stand option identifies an extra comma as an extension. For example:

  WRITE(*,*) , P(J)

• Compaq Fortran detects the use of a character variable within parentheses in an I/O statement. For example:

  CHARACTER*10 CH/'(I5)'/ INTEGER I READ CH,I ! Acceptable READ (CH),I ! Generates error message, interpreted as an internal READ END

• Compaq Fortran evaluates the exponentiation operator at compile time only if the exponent has an integer data type. Compaq Fortran 77 evaluates the exponentiation operator even when the exponent does not have an integer data type. For example:

  PARAMETER ( X = 4.0 ** 1.1)

• Compaq Fortran detects an error when evaluating constants expressions that result in an NaN or Infinity exceptional value, while Compaq Fortran 77 allows such expressions. For example:

  PARAMETER ( X = 4.0 / 0.0 )

• Compaq Fortran reports a warning error message when the same variable is initialized more than once. Compaq Fortran 77 allows multiple initializations of the same variable without a warning. For example:

  integer i data i /1/ data i /2/ write (*,*) i stop end

For More Information:

• On passing arguments and returning function values between Compaq Fortran and Compaq Fortran 77, see Section 11.3.
• On Compaq Fortran procedure calling and argument passing, see Section 11.1.
• On compatibility between Compaq Fortran for Compaq Tru64 UNIX systems and Compaq Fortran 77 on OpenVMS systems, see Section A.4.
• On the Compaq Fortran language, see the Compaq Fortran Language Reference Manual.

Compaq Fortran 77 ( f77 command) and Compaq Fortran ( f90 command) share most of the same command-line options. The following options are provided only by Compaq Fortran 77 (not by Compaq Fortran):

• -assume backslash
• -f77
• -ident
• -show xref (same as -cross_reference )
• -stand keyword
• -warn informational
• -uncalled
• -unused
• -warn nounreachable

The following options are provided only by Compaq Fortran (not by Compaq Fortran 77):

• -align recNbyte
• -assume buffered_io
• -assume gfullpath
• -assume minus0
• -f77rtl
• -fixed
• -free
• -fpconstant
• -fuse_xref (TU*X ONLY)
• -hpf_matmul (TU*X ONLY)
• -intconstant
• -module
• -ladebug
• -mp (TU*X ONLY)
• -omp (TU*X ONLY) and assorted OpenMP parallel options including -assume pthreads_lock and -check omp_bindings
• (TU*X ONLY) -wsf and associated HPF parallel options, including -assume bigarrays , -assume nozsize , -nearest_neighbor , -nowsf_main , -show hpf , -warn hpf , and -pprof
• -std (performs Fortran 95/90 standards checking, whereas the Compaq Fortran 77 -stand keyword performs FORTRAN-77 and NTT MIA standards checking)
• -warn granularity

Effective with Compaq Fortran V5.3, the f77 command by default executes the Compaq Fortran 90 compiler and uses the DECF90* environment variables. To execute the Compaq Fortran 77 compiler, use the f77 command with the -old_f77 option. This option must be the first text on the command line after f77 .

A.3 Language Compatibility with Compaq Visual Fortran

The following language features found in Compaq Visual Fortran (and Microsoft® Fortran Powerstation Version 4) are now supported by Compaq Fortran:

• # Constants. Constants using a base other than 10.
• C Strings. NULL terminated strings contain C-style escape sequences.
• Conditional Compilation And Metacommand Expressions ($define, $undefine, $if, $elseif, $else, $endif).
• $FREEFORM, $NOFREEFORM, $FIXEDFORM. Source file format
• $INTEGER, $REAL. Selects size.
• $FIXEDFORMLINESIZE. Line length for fixed form source.
• $STRICT, $NOSTRICT. F90 conformance.
• $PACK. Structure packing.
• $ATTRIBUTES ALIAS. External name for a subprogram or common block.
• $ATTRIBUTES C, STDCALL. Calling and naming conventions.
• $ATTRIBUTES VALUE, REFERENCE. Calling conventions.
• \ Descriptor. Prevents writing an end-of-record mark.
• Ew.dDe and Gw.dDe Edit Descriptors. Similar to Ew.dEe and Gw.dEe.
• 7200 Character Statement Length.
• Free form infinite line length.
• $DECLARE and $NODECLARE == IMPLICIT NONE.
• $ATTRIBUTES EXTERN. Variable allocated in another source file.
• $ATTRIBUTES VARYING. Variable number of arguments.
• $ATTRIBUTES ALLOCATABLE. Allocatable array.
• Mixing Subroutines/Functions in Generic Interfaces
• $MESSAGE. Output message during compilation.
• $LINE == C's #line
• INT1. Converts to one byte integer by truncating.
• INT2. Converts to two byte integer by truncating.
• INT4. Converts to four byte integer by truncating.
• COTAN. Returns cotangent.
• DCOTAN. Returns double precision cotangent.
• IMAG. Returns the imaginary part of complex number.
• IBCHNG. Reverses value of bit.
• ISHA. Shifts arithmetically left or right.
• ISHC. Performs a circular shift.
• ISHL. Shifts logically left or right.