G.1 DIGITAL Fortran Language Extensions

This section summarizes the DIGITAL Fortran language extensions. Most extensions are available on DIGITAL UNIX, Windows NT, Windows 95, and OpenVMS systems. However, some extensions are limited to one or more systems. If an extension is limited, it is labeled.

Source Forms

The following are extensions to the methods and rules for source forms:

• Tab-formatting as a method to code lines (see Section 2.3.2.2)

• The letter D as a debugging statement indicator in column 1 of fixed or tab source form (see Section 2.3.2)

• An optional statement field width of 132 columns for fixed or tab source form (see Section 2.3.2)

• An optional sequence number field for fixed source form (see Section 2.3.2.1)

• Up to 511 continuation lines in a source program (see Section 2.3)

As an extension, the dollar sign ($) is allowed as a valid character in names, including the first character (see Section 2.1.2).

Character Sets

The following are extensions to the Fortran 90 character set:

• The Tab (<Tab>) character (see Section 2.2)

• For OpenVMS and DIGITAL UNIX systems-the DEC Multinational extension to the ASCII character set (see Section C.2)

• For Windows NT and Windows 95 systems (see online Help):

  • Special ASCII and ANSI character sets

  • Key code sets

The following are data-type extensions (see Section 3.1):

BYTE	INTEGER*1	REAL*8 [2]
LOGICAL*1	INTEGER*2	REAL*16 [3]
LOGICAL*2	INTEGER*4	COMPLEX*8
LOGICAL*4	INTEGER*8 [1]	COMPLEX*16 [2]
LOGICAL*8 [1]	REAL*4
[1] Alpha only [2] D_floating and G_floating implementations are available on OpenVMS systems only. [3] VMS, U*X

Constants

C strings are allowed in character constants as an extension (see Section 3.1.5.1).

Hollerith constants are allowed as an extension (see Section 3.3.4).

Derived Data Types

As an extension, default initial values for derived-type components can be specified in derived-type definitions (see Section 3.2.2).

Arrays

As an extension, arrays declared using the ALLOCATABLE attribute can be automatically deallocated (see Section 6.1.1).

Expressions

When operands of different intrinsic data types are combined in expressions, conversions are performed as necessary (see Section 4.1.1.2).

Binary, octal, hexadecimal, and Hollerith constants can appear wherever numeric constants are allowed (see Section 3.3).

The following are extensions allowed in logical expressions (see Section 4.1.4):

• .XOR. as a synonym for .NEQV.

• Integers as valid logical items

As an extension, the WHERE construct can include nested WHERE constructs and a masked ELSEWHERE statement. WHERE constructs can also be named (see Section 4.2.4).

Specification Statements

The following specification attributes and statements are extensions:

• AUTOMATIC and STATIC (see Section 5.3)

• VOLATILE (see Section 5.19)

The ELEMENTAL prefix is allowed in functions and subroutines as an extension (see Sections 8.4.2 and 8.4.3). [See Note 1]

As an extension, the END INTERFACE statement of an interface block defining a generic routine can specify a generic identifier (see Section 8.8.2).

Compilation Control Statements

The following statements are extensions that can influence compilation (see Section 14.1):

• INCLUDE statement format (VMS only):

      INCLUDE '[text-lib] (module-name) [/[NO]LIST]'
  

• OPTIONS statement:

      /ASSUME = [NO]UNDERSCORE   (Alpha only)
  
               {ALL            }
               {[NO]BOUNDS     }
      /CHECK = {[NO]OVERFLOW   }
               {[NO]UNDERFLOW  }
               {NONE           }
  
      /NOCHECK
  
                 {BIG_ENDIAN     }
                 {CRAY           }
                 {FDX            }
                 {FGX            }
      /CONVERT = {IBM            }
                 {LITTLE_ENDIAN  }
                 {NATIVE         }
                 {VAXD           }
                 {VAXG           }
  
      /[NO]EXTEND_SOURCE
      /[NO]F77
  
               {D_FLOAT   (VMS only)  }
      /FLOAT = {G_FLOAT   (VMS only)  }
               {IEEE_FLOAT            }
  
      /[NO]G_FLOATING   (VMS only)
      /[NO]I4
      /[NO]RECURSIVE
  

The %VAL, %REF, %DESCR (VMS only), and %LOC built- in functions are extensions (see Section 8.7.9).

I/O Statements

The following I/O statements and specifiers are extensions:

• REWRITE statement (see Section 10.7)

• ACCEPT statement (see Section 10.4)

• TYPE statement; a synonym for the PRINT statement (see Section 10.6)

• A key-field-value specifier as a control list parameter (VMS only) (see Section 10.2.1.5)

• A key-of-reference specifier as a control list parameter (VMS only) (see Section 10.2.1.6)

• Indexed READ statement (VMS only) (see Section 10.3.3)

• Indexed WRITE statement (VMS only) (see Section 10.5.3)

As an extension, comments (beginning with !) are allowed in namelist input data.

I/O Formatting

The following are extensions allowed in I/O formatting:

• The letter Q as an edit descriptor (see Section 11.3.9)

• The dollar sign ($) as an edit descriptor (see Section 11.3.8 and as a carriage control character (see Section 11.7)

• The backslash character (\) as an edit descriptor (see Section 11.3.8)

• ASCII NUL as a carriage control character (see Section 11.7)

• Variable format expressions (see Section 11.6)

• On output, when using I, B, O, Z, and F edit descriptors, the specified value of the field width can be zero (see Section 11.2.2).

The following intrinsic procedures are extensions (see Chapter 9):

ACOSD	COTAN	IARGCOUNT [2]	NWORKERS
ASIND	CPU_TIME	IARGPTR	QEXT [3]
ATAND	DATE	IBCHNG	QFLOAT [3]
ATAN2D	DCMPLX	IDATE	RAN
CDABS [1]	DFLOAT	ISHA	RANDU
CDCOS [1]	DREAL	ISHC	SECNDS
CDEXP [1]	EOF	ISHL	SIND
CDLOG [1]	ERRSNS	ISNAN	SIZEOF
CDSIN [1]	EXIT	LOC	TAND
CDSQRT [1]	FP_CLASS	MALLOC	TIME
COSD	FREE	NULL	ZEXT
[1] Double precision complex intrinsics can also begin with the letter Z (see Chapter 9). For example, CDABS can also be spelled ZABS. [2] VMS only [3] VMS, U*X

The following INTEGER(8) specific functions are extensions available on Alpha processors (see Chapter 9):

AKMAX0	KIBCLR	KIFIX	KMIN0
AKMIN0	KIBITS	KINT	KMIN1
BKTEST	KIBSET	KIOR	KMOD
DFLOTK	KIDIM	KISHFT	KNINT
FLOATK	KIDINT	KISIGN	KNOT
KIABS	KIDNNT	KMAX0	KZEXT
KIAND	KIEOR	KMAX1

As an extension, the keyword KIND can be specified for CEILING and FLOOR (see Sections 9.3.22 and 9.3.50, respectively).

As an extension, SIGN can distinguish between positive and negative zero (see Section 9.3.132).

Additional Language Features

The following are language extensions that facilitate compatibility with other versions of Fortran:

• DEFINE FILE statement (see Section B.1)

• ENCODE and DECODE statements (see Section B.2)

• FIND statement (see Section B.3)

• An alternative syntax for the PARAMETER statement (see Section B.4)

• VIRTUAL statement (see Section B.5)

• AND, OR, XOR, IMAG, LSHIFT, RSHIFT intrinsics (see Table 9-3)

• An alternative syntax for octal and hexadecimal constants (see Section B.6)

• An alternative syntax for an I/O record specifier (see Section B.7)

• An alternate syntax for the DELETE statement (see Section B.8)

• An alternative form for namelist external records (see Section B.9)

• The DIGITAL Fortran POINTER statement (see Section B.10)

• Record structures (see Section B.11)

Run-time library module routines are available for Windows NT and Windows 95 systems (see Appendix E). Some of these routines are also available as 3f library routines on DIGITAL UNIX systems.

Note 1: The PURE prefix is also allowed as an HPF language extension.