HP OpenVMS Systems Documentation

HP Fortran for OpenVMS
User Manual

This section lists Compaq Fortran 77 extensions to the FORTRAN-77 standard that are interpretation differences or are not included in HP Fortran for OpenVMS I64 or OpenVMS Alpha systems. Where appropriate, this list indicates equivalent HP Fortran language features.

HP Fortran conforms to the Fortran 90 and Fortran 95 standards. The Fortran 90 standard is a superset of the FORTRAN-77 standard. The Fortran 95 standard deletes some FORTRAN-77 features from the Fortran 90 standard. HP Fortran fully supports all of these deleted features (see the HP Fortran for OpenVMS Language Reference Manual).

HP Fortran provides many but not all of the FORTRAN-77 extensions provided by Compaq Fortran 77.

B.3.1 Compaq Fortran 77 for OpenVMS Language Features Not Implemented

The following FORTRAN-77 extensions provided by Compaq Fortran 77 on OpenVMS systems (both Alpha and VAX hardware) are not provided by HP Fortran for OpenVMS I64 or OpenVMS Alpha systems:

• Octal notation for integer constants is not part of the HP Fortran language. Compaq Fortran 77 for OpenVMS Alpha Systems supports this feature only when the /VMS qualifier is in effect (default). For example:

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

• The HP Fortran language prohibits dummy arguments with nonconstant bounds from being a namelist item. For example:

  SUBROUTINE FOO(A,N) DIMENSION A(N),B(10) NAMELIST /N1/ A ! Incorrect NAMELIST /N2/ B ! Correct END SUBROUTINE

• HP 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

Certain language features are available in Compaq Fortran 77 for OpenVMS VAX systems, but are not supported in HP Fortran for OpenVMS I64 or OpenVMS Alpha systems. These features include features supported by the VAX architecture, VAX hardware support, and older language extensions:

• Automatic decomposition features of FORTRAN /PARALLEL=(AUTOMATIC). For information on a performance preprocessor that allows parallel execution, see Section 5.1.1.
• Manual (directed) decomposition features of FORTRAN /PARALLEL=(MANUAL) using the CPAR$ directives, such as CPAR$ DO_PARALLEL. For information on a performance preprocessor that allows parallel execution, see Section 5.1.1.
• The following I/O and error subroutines for PDP-11 compatibility:

  ASSIGN CLOSE ERRSET

  ERRTST FDBSET IRAD50

  RAD50 R50ASC USEREX

  
  When porting existing programs, calls to ASSIGN, CLOSE, and FBDSET should be replaced with the appropriate OPEN statement. (You might consider converting DEFINE FILE statements at the same time, even though HP Fortran does support the DEFINE FILE statement.)
  In place of ERRSET and ERRTST, OpenVMS condition handling might be used.
• Radix-50 constants in the form nRxxx
  For existing programs being ported, radix 50 constants and the IRAD50, RAD50 and R50ASC routines should be replaced by data encoded in ASCII using CHARACTER declared data.
• Numeric local variables are usually (but not always) initialized to a zero value, depending on the level of optimization used. To guarantee that a value will be initialized to zero under all circumstances, use an explicit assignment or DATA statement.
• Character constant actual arguments must be associated with character dummy arguments, not numeric dummy arguments, if source program units are compiled separately. (Compaq Fortran 77 for OpenVMS VAX Systems passed 'A' by reference if the dummy argument was numeric.)
  To allow character constant actual arguments to be associated with numeric dummy arguments, specify the /BY_REF_CALL qualifier on the FORTRAN command line (see Section 2.3.9).

The following language features are available in Compaq Fortran 77 for OpenVMS VAX systems, but are not supported in HP Fortran because of architectural differences between OpenVMS I64 and OpenVMS Alpha systems and OpenVMS VAX systems:

• Certain FORSYSDEF symbol definition library modules might be specific to the VAX or Itanium or Alpha architecture. For information on FORSYSDEF text library modules, see Appendix E.
• Precise exception control
  Compaq Fortran 77 for OpenVMS VAX Systems provides precise reporting of run-time exceptions. For performance reasons on OpenVMS I64 and OpenVMS Alpha systems, the default FORTRAN command behavior is that exceptions are usually reported after the instruction causing the exception. You can request precise exception reporting using the FORTRAN command /SYNCHRONOUS_EXCEPTIONS (Alpha only) qualifier (see Section 2.3.46). For information on error and condition handling, see Chapter 7 and Chapter 14.
• The REAL*16 H_float data type supported on OpenVMS VAX systems
  The REAL (KIND=16) floating-point format on OpenVMS I64 and OpenVMS Alpha systems is X_float (see Chapter 8). For information on the VAX H_float data type, see Section B.8.
• VAX support for D_float, F_float, and G_float
  The OpenVMS Alpha instruction set does not support D_float computations, and the OpenVMS I64 instruction set does not support D_float, F_float or G_float computations. As a result, any data stored in those formats is converted to a native format for arithmetic computations and then converted back to its original format. On Alpha systems, the native format used for D_float is G_float. On I64 systems, S_float is used for F_float data, and T_float is used for D_float and G_float data.
  This means that for programs that perform many floating-point computations, using D_float data on Alpha systems is slower than using G_float or T_float data. Similarly, using D_float, F_float, or G_float data on I64 systems is slower than using S_float or T_float data. Additionally, due to the conversions involved, the results might differ from native VAX D_float, F_float, and G_float computations and results.
  Use the /FLOAT qualifier to specify the floating-point format (see Section 2.3.22).
  To create an HP Fortran application program to convert D_float data to G_float or T_float format, use the file conversion methods described in Chapter 9.
• Vectorization capabilities
  Vectorization, including /VECTOR and its related qualifiers, and the CDEC$ INIT_DEP_FWD directive are not supported. The Alpha processor provides instruction pipelining and other features that resemble vectorization capabilities.

The following FORTRAN-77 extensions provided by Compaq Fortran 77 on OpenVMS systems (both Alpha and VAX hardware) are interpreted differently by HP Fortran.

• The HP 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, whereas HP Fortran evaluates the constant in single precision (by default).
  You can request that a single-precision constant assigned to a double-precision variable be evaluated in double precision, specify the FORTRAN command /ASSUME=FP_CONSTANT qualifier. The Fortran 90 standard requires that the constant be evaluated in single precision, but this can make calculated results differ between Compaq Fortran 77 and HP Fortran.
  In the example below, Compaq Fortran 77 assigns identical values to D1 and D2, whereas HP 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 HP 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, HP Fortran uses the syntax for namelist external records specified by the Fortran 90 standard, rather than the Compaq Fortran 77 syntax (an extension to the FORTRAN-77 and Fortran 90 standards).
  Consider the following program:

  INTEGER I NAMELIST /N/ I I = 5 PRINT N END

  
  When this program is run after being compiled by the FORTRAN command, the following output appears:

  $ FORTRAN TEST.F $ LINK TEST $ RUN TEST &N I = 5 /

  
  When this program is run after being compiled by the FORTRAN command with the /OLDF77 qualifier, the following output appears:

  $ FORTRAN /OLDF77 TEST.F $ LINK TEST $ RUN TEST $N I = 5 $END

  
  HP Fortran accepts Fortran 90 namelist syntax and Compaq Fortran 77 namelist syntax for reading records.
• HP Fortran does not support C-style escape sequences in standard character literals. Use the C string literal syntax extension or the CHAR intrinsic instead. For example:

  CHARACTER*2 CRLF CRLF = '\r\n' ! Incorrect CRLF = '\r\n'C ! Correct CRLF = CHAR(13)//CHAR(10) ! Standard-conforming alternative

• HP Fortran inserts a leading blank when doing list-directed I/O to an internal file. Compaq Fortran 77 does this only when the /VMS qualifier is in effect (default) on OpenVMS Alpha Systems. For example:

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

• Compaq Fortran 77 and HP Fortran produce different output for 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) ! HP Fortran prints 0.000

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

  REAL A(SQRT(31.5)) END

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

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

• HP Fortran does not allow extraneous parentheses in I/O lists. For example:

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

• HP Fortran does not allow control characters within quoted strings, unless you use the C-string extension. For example:

  character*5 c c = 'ab\nef' ! not allowed c = 'ab\nef'C ! allowed end

• HP 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.
  HP 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 HP Fortran:

  REAL*8 R R = 'abc' // 'def' WRITE (6,*) R END

  
  HP Fortran does allow PARAMETER constants:

  PARAMETER abcdef = 'abc' // 'def' REAL*8 R R = abcdef WRITE (6,*) 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, HP 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 an HP Fortran program.

For More Information:

• On argument passing between HP Fortran and Compaq Fortran 77, see Section 10.9.
• On the HP Fortran language, see the HP Fortran for OpenVMS Language Reference Manual.

The following language features are interpreted differently in Compaq Fortran 77 for OpenVMS VAX Systems and HP Fortran for OpenVMS I64 or OpenVMS Alpha systems:

• Random number generator (RAN)
  The RAN function generates a different pattern of numbers in HP Fortran than in Compaq Fortran 77 for OpenVMS VAX Systems for the same random seed. (The RAN and RANDU functions are provided for Compaq Fortran 77 for OpenVMS VAX Systems compatibility. See the HP Fortran for OpenVMS Language Reference Manual.)
• INQUIRE(RECL) for unformatted files
  INQUIRE(RECL) for unformatted files with the default RECL unit (longwords) gives different answers for Compaq Fortran 77 for OpenVMS VAX Systems and HP Fortran if the existing file has a record length that is not a multiple of 4 bytes. To prevent this difference, use /ASSUME=BYTERECL and specify the proper RECL in bytes in the OPEN statement.
• Hollerith constants in formatted I/O statements
  Compaq Fortran 77 for OpenVMS VAX Systems and HP Fortran behave differently if either of the following occurs:
  • Two different I/O statements refer to the same CHARACTER PARAMETER constant as their format specifier, for example:

    CHARACTER*(*) FMT2 PARAMETER (FMT2='(10Habcdefghij)') READ (5, FMT2) WRITE (6, FMT2)

  • Two different I/O statements use the identical character constant as their format specifier, for example:

    READ (5, '(10Habcdefghij)') WRITE (6, '(10Habcdefghij)')

  
  In Compaq Fortran 77 for OpenVMS VAX Systems, the value obtained by the READ statement is the output of the WRITE statement (FMT2 is ignored). However, in HP Fortran, the output of the WRITE statement is "abcdefghij". (The value read by the READ statement has no effect on the value written by the WRITE statement.)

The following language features are detected differently by HP Fortran than Compaq Fortran 77:

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

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

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

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

• The HP Fortran compiler enforces the constraint that a branch to a statement shared by one more 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 HP 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 HP 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 HP 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 from integer overflow I8 = 2147483647_8 + 1_8 ! Correct

• The HP 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 HP Fortran compiler enforces the constraint that certain intrinsic procedures defined by the Fortran 95 standard cannot be passed as actual arguments. For example, Compaq Fortran 77 allows most intrinsic procedures to be passed as actual arguments, but the HP Fortran compiler only allows those defined by the Fortran 95 standard (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 90 standard.
• HP Fortran reports character truncation with an error-level message, not as a warning.
  The following program produces an error message during compilation with HP 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 HP Fortran intrinsic procedures with the wrong number of arguments or an incorrect argument type, HP Fortran reports this with an error-level message, not with a warning. Possible causes include:
  • An HP 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 HP 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

• HP 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 HP 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)

• HP 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).
• HP Fortran does not detect an extra comma in an I/O statement when the /STANDARD qualifier is specified, whereas Compaq Fortran 77 with the same qualifier identifies an extra comma as an extension. For example:

  WRITE(*,*) , P(J)

• HP 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

• HP 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)

• HP 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:

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