HP OpenVMS Systems Documentation

HP Fortran for OpenVMS
Language Reference Manual

A nonpointer array occupies a sequence of contiguous storage sequences, one for each array element, in array element order.

Two or more arrays are associated when each one is associated with the same storage location. They are partially associated when part of the storage associated with one array is the same as part or all of the storage associated with another array.

If arrays with different data types are associated (or partially associated) with the same storage location, and the value of one array is defined (for example, by assignment), the value of the other array becomes undefined. This happens because an element of an array is considered defined only if the storage associated with it contains data of the same type as the array name.

An array element, array section, or whole array is defined by a DATA statement before program execution. (The array properties must be declared in a previous specification statement.) During program execution, array elements and sections are defined by an assignment or input statement, and entire arrays are defined by input statements.

For More Information:

• On arrays, see Section 3.5.2.
• On array element order, see Section 3.5.2.2.
• On the DATA statement, see Section 5.5.

This appendix describes deleted and obsolescent language features.

Fortran 90 identified certain FORTRAN 77 features to be obsolescent. Fortran 95 deleted some of these features, and identified a few more language features to be obsolescent. Features considered obsolescent might be removed from future revisions of the Fortran Standard.

You can specify a compiler option to have these features flagged.

Some language features, considered redundant in FORTRAN 77, are not included in Fortran 95. However, they are still fully supported by HP Fortran:

• ASSIGN and assigned GO TO statements
• Assigned FORMAT specifier
• Branching to an END IF statement from outside its IF block
• H edit descriptor
• PAUSE statement
• Real and double precision DO control variables and DO loop control expressions

For suggested methods to achieve the functionality of these features, see Section A.3.

A.2 Obsolescent Language Features in Fortran 95

Some language features considered redundant in Fortran 90 are identified as obsolescent in Fortran 95.

Other methods are suggested to achieve the functionality of the following obsolescent features:

• Alternate returns
  To replace this functionality, it is recommended that you use an integer variable to return a value to the calling program, and let the calling program use a CASE construct to test the value and perform operations (see Section 7.4).
• Arithmetic IF
  To replace this functionality, it is recommended that you use an IF statement or construct (see Section 7.8).
• Assumed-length character functions
  To replace this functionality, it is recommended that you use one of the following:
  • An automatic character-length function, where the length of the function result is declared in a specification expression
  • A subroutine whose arguments correspond to the function result and the function arguments
  
  Dummy arguments of a function can still have assumed character length; this feature is not obsolescent.
• CHARACTER*(*) form of CHARACTER declaration
  To replace this functionality, it is recommended that you use the Fortran 90 forms of specifying a length selector in CHARACTER declarations (see Section 5.1.2).
• Computed GO TO statement
  To replace this functionality, it is recommended that you use a CASE construct (see Section 7.4).

• DATA statements among executable statements
  This functionality has been included since FORTRAN 66, but is considered to be a potential source of errors.
• Fixed source form
  Newer methods of entering data have made this source form obsolescent and error-prone.
  The recommended method for coding is to use free source form (see Section 2.3.1).
• Shared DO termination and termination on a statement other than END DO or CONTINUE
  To replace this functionality, it is recommended that you use an END DO statement (see Section 7.6.1) or a CONTINUE statement (see Section 7.5).
• Statement functions
  To replace this functionality, it is recommended that you use an internal function (see Section 8.7).

Fortran 90 did not delete any of the features in FORTRAN 77, but some FORTRAN 77 features were identified as obsolescent.

Other methods are suggested to achieve the functionality of the following obsolescent features:

• Alternate return (labels in an argument list)
  To replace this functionality, it is recommended that you use an integer variable to return a value to the calling program, and let the calling program test the value and perform operations, using a computed GO TO statement (see Section 7.2.2) or CASE construct (see Section 7.4).
• Arithmetic IF
  To replace this functionality, it is recommended that you use an IF statement or construct (see Section 7.8).

• ASSIGN and assigned GO TO statements
  These statements are usually used to simulate internal procedures (see Section 8.7), which can now be coded directly.
• Assigned FORMAT specifier (label of a FORMAT statement assigned to an integer variable)
  To replace this functionality, it is recommended that you use character expressions to define format specifications (see Section 11.2).
• Branching to an END IF statement from outside its IF block
  To replace this functionality, it is recommended that you branch to the statement following the END IF statement (see Section 7.8.1).
• H edit descriptor
  To replace this functionality, it is recommended that you use the character constant edit descriptor (see Section 11.5).
• PAUSE statement
  To replace this functionality, it is recommended that you use a READ statement that awaits input data (see Section 10.3).
• Real and double precision DO control variables and DO loop control expressions
  To replace this functionality, it is recommended that you use integer DO variables and expressions (see Section 7.6).
• Shared DO termination and termination on a statement other than END DO or CONTINUE
  To replace this functionality, it is recommended that you use an END DO statement (see Section 7.6.1) or a CONTINUE statement (see Section 7.5).

This appendix describes additional language features provided by HP Fortran to facilitate compatibility with older versions of Fortran.

Rules and Behavior

The DEFINE FILE statement specifies that a file containing m fixed-length records, each composed of n 16-bit words, exists (or will exist) on the specified logical unit. The records in the file are numbered sequentially from 1 through m.

A DEFINE FILE statement does not itself open a file. However, the statement must be executed before the first direct access I/O statement referring to the specified file. The file is opened when the I/O statement is executed.

If this I/O statement is a WRITE statement, a direct access sequential file is opened, or created if necessary.

If the I/O statement is a READ or FIND statement, an existing file is opened, unless the specified file does not exist. If a file does not exist, an error occurs.

The DEFINE FILE statement establishes the variable asv as the associated variable of a file. At the end of each direct access I/O operation, the Fortran I/O system places in asv the record number of the record immediately following the one just read or written.

The associated variable always points to the next sequential record in the file (unless the associated variable is redefined by an assignment, input, or FIND statement). So, direct access I/O statements can perform sequential processing on the file by using the associated variable of the file as the record number specifier.

Examples

In the following example, the DEFINE FILE statement specifies that the logical unit 3 is to be connected to a file of 1000 fixed-length records; each record is 48 16-bit words long. The records are numbered sequentially from 1 through 1000 and are unformatted. After each direct access I/O operation on this file, the integer variable NREC will contain the record number of the record immediately following the record just processed.

DEFINE FILE 3(1000,48,U,NREC)

Rules and Behavior

The number of characters that the ENCODE or DECODE statement can translate depends on the data type of b. For example, an INTEGER (2) array can contain two characters per element, so that the maximum number of characters is twice the number of elements in that array.

The maximum number of characters a character variable or character array element can contain is the length of the character variable or character array element.

The maximum number of characters a character array can contain is the length of each element multiplied by the number of elements.

Examples

In the following example, the DECODE statement translates the 12 characters in A to integer form (as specified by the FORMAT statement):

     DIMENSION K(3)
     CHARACTER*12 A,B
     DATA A/'123456789012'/
     DECODE(12,100,A) K
100  FORMAT(3I4)
     ENCODE(12,100,B) K(3), K(2), K(1)

K(1) = 1234
K(2) = 5678
K(3) = 9012

B = '901256781234'

For More Information:

• On internal READ statements, see Section 10.3.4.
• On internal WRITE statements, see Section 10.5.4.

Examples

In the following example, the FIND statement positions logical unit 1 at the first record in the file. The file's associated variable is set to one:

FIND(1, REC=1)

FIND(4, REC=INDX)

For More Information:

On direct access READ statements, see Section 10.3.2.

B.4 FORTRAN-66 Interpretation of the EXTERNAL Statement

Main Program                        Subprograms

EXTERNAL SIN, COS, *TAN, SINDEG     SUBROUTINE TRIG(X,F,Y)
   .                                Y = F(X)
   .                                RETURN
   .                                END
CALL TRIG(ANGLE, SIN, SINE)
   .
   .                                FUNCTION TAN(X)
   .                                TAN = SIN(X)/COS(X)
CALL TRIG(ANGLE, COS, COSINE)       RETURN
   .                                END
   .
   .
CALL TRIG(ANGLE, TAN, TANGNT)       FUNCTION SINDEG(X)
   .                                SINDEG = SIN(X*3.1459/180)
   .                                RETURN
   .                                END
CALL TRIG(ANGLED, SINDEG, SINE)

Y = SIN(X)
Y = COS(X)
Y = TAN(X)
Y = SINDEG(X)

The functions SIN and COS are examples of trigonometric functions supplied in the Fortran 95/90 library. The function TAN is also supplied in the library, but the asterisk (*) in the EXTERNAL statement specifies that the user-supplied function be used, instead of the library function. The function SINDEG is also a user-supplied function. Because no library function has the same name, no asterisk is required.

For More Information:

On Fortran 95/90 intrinsic functions, see Chapter 9.

B.5 Alternative Syntax for the PARAMETER Statement

The PARAMETER statement discussed here is similar to the one discussed in Section 5.14; they both assign a name to a constant. However, this PARAMETER statement differs from the other one in the following ways:

• Its list is not bounded with parentheses.
• The form of the constant, rather than implicit or explicit typing of the name, determines the data type of the variable.

Rules and Behavior

Each name c becomes a constant and is defined as the value of expression expr. Once a name is defined as a constant, it can appear in any position in which a constant is allowed. The effect is the same as if the constant were written there instead of the name.

The name of a constant cannot appear as part of another constant, except as the real or imaginary part of a complex constant. For example:

PARAMETER I=3
PARAMETER M=I.25        ! Not allowed
PARAMETER N=(1.703, I)  ! Allowed

PARAMETER  PI=3.1415927, DPI=3.141592653589793238D0
PARAMETER  PIOV2=PI/2, DPIOV2=DPI/2
PARAMETER  FLAG=.TRUE., LONGNAME='A STRING OF 25 CHARACTERS'

For More Information:

On compile-time constant expressions, see Section 5.14.