HP Fortran provides compiler directives to perform general-purpose tasks during compilation. You do not need to specify a compiler option to enable general directives.

The following general syntax rules apply to all general compiler directives. You must follow these rules precisely to compile your program properly and obtain meaningful results.

A general directive prefix (tag) takes the following form:

c

Is one of the following: C (or c), !, or *.

The following are source form rules for directive prefixes:

• Prefixes beginning with C (or c) and * are only allowed in fixed and tab source forms.
  In these source forms, the prefix must appear in columns 1 through 5; column 6 must be a blank or tab. From column 7 on, blanks are insignificant, so the directive can be positioned anywhere on the line after column 6.
• Prefixes beginning with ! are allowed in all source forms.
  The prefix can appear in any valid column, but it cannot be preceded by any nonblank characters on the same line. It can only be preceded by whitespace.

A general directive ends in column 72 (or column 132, if a compiler option is specified).

General directives cannot be continued.

A comment can follow a directive on the same line.

Additional Fortran statements (or directives) cannot appear on the same line as the general directive.

General directives cannot appear within a continued Fortran statement.

The ALIAS directive lets you specify an alternate external name to be used when referring to external subprograms. This can be useful when compiling applications written for other platforms that have different naming conventions.

The ALIAS directive takes the following form:

c

Is one of the following: C (or c), !, or * (see Section 14.1).

internal-name

Is the name of the subprogram as used in the current program unit.

external-name

Is a name, or a character constant delimited by apostrophes or quotation marks.

If a name is specified, the name (in uppercase) is used as the external name for the specified internal-name. If a character constant is specified, it is used as is; the string is not changed to uppercase, nor are blanks removed.

The ALIAS directive affects only the external name used for references to the specified internal-name.

The ATTRIBUTES directive lets you specify properties for data objects and procedures. It takes the following form: ¹

c

Is one of the following: C (or c), !, or * (see Section 14.1).

att

Is one of the following:

ADDRESS64	DESCRIPTOR32	REFERENCE
ALIAS	DESCRIPTOR64	REFERENCE32
ALLOW_NULL		REFERENCE64
		STDCALL
C	EXTERN	VALUE
DECORATE	IGNORE_LOC	VARYING
DEFAULT	NO_ARG_CHECK
DESCRIPTOR	NOMIXED_STR_LEN_ARG

object

Is the name of a data object or procedure.

The following table shows which properties can be used with various objects:

These properties can be used in function and subroutine definitions, in type declarations, and with the INTERFACE and ENTRY statements.

Properties applied to entities available through use or host association are in effect during the association. For example, consider the following:

MODULE MOD1
  INTERFACE
    SUBROUTINE SUB1
    !DEC$ ATTRIBUTES C, ALIAS:'othername' :: NEW_SUB
    END SUBROUTINE
  END INTERFACE
  CONTAINS
    SUBROUTINE SUB2
    CALL NEW_SUB
    END SUBROUTINE
END MODULE

In this case, the call to NEW_SUB within SUB2 uses the C and ALIAS properties specified in the interface block.

The properties are described as follows:

• ADDRESS64
  Specifies that the object has a 64-bit address. This property can be specified for any variable or dummy argument, including ALLOCATABLE and deferred-shape arrays. However, variables with this property cannot be data-initialized.
  It can also be specified for COMMON blocks or for variables in a COMMON block. If specified for a COMMON block variable, the COMMON block implicitly has the ADDRESS64 property.
  ADDRESS64 is not compatible with the AUTOMATIC attribute.
• ALIAS
  Specifies an alternate external name to be used when referring to external subprograms. Its form is:

  ALIAS:external-name

  external-name

  Is a character constant delimited by apostrophes or quotation marks. The character constant is used as is; the string is not changed to uppercase, nor are blanks removed.

  
  The ALIAS property overrides the C (and STDCALL) property. If both C and ALIAS are specified for a subprogram, the subprogram is given the C calling convention, but not the C naming convention. It instead receives the name given for ALIAS, with no modifications.
  ALIAS cannot be used with internal procedures, and it cannot be applied to dummy arguments.
  cDEC$ ATTRIBUTES ALIAS has the same effect as the cDEC$ ALIAS directive (see Section 14.2).
• ALLOW_NULL
  Enables a corresponding dummy argument to pass a NULL pointer (defined by a zero or the NULL intrinsic function) by value for the argument.
  ALLOW_NULL is only valid if the REFERENCE property is also specified; otherwise, it has no effect.
• C and STDCALL
  Specify how data is to be passed when you use routines written in C or assembler with FORTRAN or Fortran 95/90 routines.
  C and STDCALL are synonyms.
  When applied to a subprogram, these properties define the subprogram as having a specific set of calling conventions.
  The following table summarizes the differences between the calling conventions:

  Convention	C1	STDCALL1	Default2
  Arguments passed by value	Yes	Yes	No

  ---

  ¹C and STDCALL are synonyms.
  ²Fortran 95/90 calling convention.
  

  ---

  
  If C or STDCALL is specified for a subprogram, arguments (except for arrays and characters) are passed by value. Subprograms using standard Fortran 95/90 conventions pass arguments by reference.
  Character arguments are passed as follows:
  • By default, hidden lengths are put at the end of the argument list.
  • If C or STDCALL (only) is specified, the first character of the string is passed (and padded with zeros out to INTEGER(4) length).
  • If C or STDCALL is specified, and REFERENCE is specified for the argument, the string is passed but the length is not passed.
  • If C or STDCALL is specified, and REFERENCE is specified for the routine (but REFERENCE is not specified for the argument, if any), the string is passed but the length is not passed.
  
  For details, see information on mixed-language programming in the HP Fortran for OpenVMS User Manual. See also the description of REFERENCE in this list.
• DECORATE
  Specifies that the external name used in cDEC$ ALIAS or cDEC$ ATTRIBUTES ALIAS should have the prefix and postfix decorations performed on it that are associated with the calling mechanism that is in effect. These are the same decorations performed on the procedure name when ALIAS is not specified.
  The case of the external name is not modified.
  If ALIAS is not specified, this property has no effect.
  See also the summary of prefix and postfix decorations in the above description of ATTRIBUTES options C and STDCALL.
• DEFAULT
  Overrides certain compiler options that can affect external routine and COMMON block declarations.
  It specifies that the compiler should ignore compiler options that change the default conventions for external symbol naming and argument passing for routines and COMMON blocks.
  This option can be combined with other cDEC$ ATTRIBUTES options, such as STDCALL, C, REFERENCE, ALIAS, etc. to specify attributes different from the compiler defaults.
  This option is useful when declaring INTERFACE blocks for external routines, since it prevents compiler options from changing calling or naming conventions.
• DESCRIPTOR
  Specifies that the argument is passed by VMS descriptor. This property can be specified only for dummy arguments in an INTERFACE block (not for a routine name).
• DESCRIPTOR32
  Specifies that the argument is passed as a 32-bit descriptor.
• DESCRIPTOR64
  Specifies that the argument is passed as a 64-bit descriptor.
• EXTERN
  Specifies that a variable is allocated in another source file. EXTERN can be used in global variable declarations, but it must not be applied to dummy arguments.
  EXTERN must be used when accessing variables declared in other languages.
• IGNORE_LOC
  Enables %LOC to be stripped from an argument.
  IGNORE_LOC is only valid if the REFERENCE property is also specified; otherwise, it has no effect.
• NO_ARG_CHECK
  Specifies that type and shape matching rules related to explicit interfaces are to be ignored. This permits the construction of an INTERFACE block for an external procedure or a module procedure that accepts an argument of any type or shape; for example, a memory copying routine.
  NO_ARG_CHECK can appear only in an INTERFACE block for a non-generic procedure or in a module procedure. It can be applied to an individual dummy argument name or to the routine name, in which case the property is applied to all dummy arguments in that interface.
  NO_ARG_CHECK cannot be used for procedures with the PURE or ELEMENTAL prefix. If an argument has an INTENT or OPTIONAL attribute, any NO_ARG_CHECK specification is ignored.
• NOMIXED_STR_LEN_ARG
  Specifies that hidden lengths be placed in sequential order at the end of the argument list.
• REFERENCE and VALUE
  Specify how a dummy argument is to be passed.
  REFERENCE specifies a dummy argument's memory location is to be passed instead of the argument's value.
  VALUE specifies a dummy argument's value is to be passed instead of the argument's memory location.
  When a dummy argument has the VALUE property, the actual argument passed to it can be of a different type. If necessary, type conversion is performed before the subprogram is called.
  When a complex (KIND=4 or KIND=8) argument is passed by value, two floating-point arguments (one containing the real part, the other containing the imaginary part) are passed by immediate value.
  Character values, substrings, assumed-size arrays, and adjustable arrays cannot be passed by value.
  If REFERENCE (only) is specified for a character argument, the string is passed but the length is not passed.
  If REFERENCE is specified for a character argument, and C (or STDCALL) has been specified for the routine, the string is passed with no length. This is true even if REFERENCE is also specified for the routine.
  If REFERENCE and C (or STDCALL) are specified for a routine, but REFERENCE has not been specified for the argument, the string is passed with the length.
  VALUE is the default if the C or STDCALL property is specified in the subprogram definition.
  For more details, see information on mixed-language programming in the HP Fortran for OpenVMS User Manual.
• REFERENCE32
  Specifies that the argument is accepted only by 32-bit address.
• REFERENCE64
  Specifies that the argument is accepted only by 64-bit address.
• VARYING
  Allows a variable number of calling arguments. If VARYING is specified, the C property must also be specified.
  Either the first argument must be a number indicating how many arguments to process, or the last argument must be a special marker (such as --1) indicating it is the final argument. The sequence of the arguments, and types and kinds must be compatible with the called procedure.

Options C, STDCALL, REFERENCE, VALUE, and VARYING affect the calling conventions of routines:

• You can specify C, STDCALL, REFERENCE, and VARYING for an entire routine.
• You can specify VALUE and REFERENCE for individual arguments.

The DECLARE directive generates warnings for variables that have been used but have not been declared (like the IMPLICIT NONE statement). The NODECLARE directive (the default) disables these warnings.

The DECLARE and NODECLARE directives take the following forms: ¹

c

Is one of the following: C (or c), !, or * (see Section 14.1).