Compatibility with Compaq Fortran on Other Platforms

Compaq Visual Fortran supports extensions to the Fortran 95 and 90 ISO and ANSI standards, including a number of extensions defined by:

Compaq Fortran (formerly Digital Fortran)
Compaq Fortran (including Compaq Visual Fortran) provides many of the language extensions provided by Compaq Fortran 77 for OpenVMS VAX Systems (formerly DEC Fortran 77 and VAX FORTRAN).
Microsoft Fortran PowerStation 4.0
For information about Microsoft Fortran PowerStation 4.0, see Compatibility with Microsoft Fortran PowerStation.

This section discusses the following topics:

Summary of Language Compatibility
Common Language Extensions
Major Changes from the FORTRAN 77 to Fortran 95 Standards
Platform Porting Notes

Summary of Language Compatibility

Compaq Visual Fortran (CVF) uses the same robust, highly efficient Fortran 95/90 compiler used by Compaq Fortran for the following Alpha operating systems:

Compaq Tru64 UNIX Alpha systems
Linux Alpha systems
Compaq OpenVMS Alpha systems

The following table summarizes the compatibility of Compaq Visual Fortran with Compaq Fortran for Alpha systems and Compaq Fortran 77 (CF77) for OpenVMS VAX systems:

Summary of Language Compatibility

	Compaq Fortran (CF) OS/Architecture Platform
Language Feature	CVF Windows	CF UNIX Alpha	CF Linux Alpha	CF OpenVMS Alpha	CF77 OpenVMS VAX
Linking against static and shared libraries	X	X	X	X	X
Create code for shared libraries	X	X	X	X	X
Recursive code support	X	X	X	X	X
AUTOMATIC and STATIC statements	X	X	X	X	X
STRUCTURE and RECORD declarations	X	X	X	X	X
INTEGER1, 2, *4	X	X	X	X	X
LOGICAL1, 2, *4	X	X	X	X	X
INTEGER8 and LOGICAL8	X	X	X	X
REAL4, 8	X	X	X	X	X
REAL*16¹		X	X	X	X
COMPLEX8, 16	X	X	X	X	X
COMPLEX*32²		X	X	X
POINTER (CRAY-style)	X	X	X	X	X
INCLUDE statement	X	X	X	X	X
IMPLICIT NONE statement	X	X	X	X	X
Data initialization in type declarations	X	X	X	X	X
Automatic arrays	X	X	X	X
VOLATILE statements	X	X	X	X	X
NAMELIST-directed I/O	X	X	X	X	X
31-character names including $ and _	X	X	X	X	X
Source listing with machine code	X	X	X	X	X
Debug statements in source	X	X	X	X	X
Bit constants to initialize data and use in arithmetic	X	X	X	X	X
DO WHILE and END DO statements	X	X	X	X	X
Built-in functions %LOC, %REF, %VAL	X	X	X	X	X
SELECT CASE construct	X	X	X	X
EXIT and CYCLE statements	X	X	X	X
Variable FORMAT expressions (VFEs)	X	X	X	X	X
! marks end-of-line comment	X	X	X	X	X
Optional run-time bounds checking for arrays and substrings	X	X	X	X	X
Binary (unformatted) I/O in IEEE big endian, IEEE little endian, VAX, IBM, and CRAY floating-point formats	X	X	X	X	X
Fortran 95/90 standards checking	X	X	X	X
FORTRAN-77 standards checking					X
IEEE exception handling	X	X	X	X
VAX floating data type in memory				X	X
IEEE floating data type in memory	X	X	X	X
CDD/Repository DICTIONARY support					X
KEYED access and INDEXED files				X	X
Parallel decomposition	⁴	X^3,4		⁴	X
OpenMP parallel directives		X
Conditional compilation using IF...DEF constructs	X	X	X	X
Vector code support					X
Direct inlining of Basic Linear Algebra Subroutines (BLAS)	⁵	⁵	⁵	⁵	X
DATE_AND_TIME returns 4-digit year	X	X	X	X	X
FORALL statement and construct	X	X	X	X
Automatic deallocation of ALLOCATABLE arrays	X	X	X	X
Dim argument to MAXLOC and MINLOC	X	X	X	X
PURE user-defined subprograms	X	X	X	X
ELEMENTAL user-defined subprograms	X	X	X	X
Pointer initialization (initial value)	X	X	X	X
The NULL intrinsic to nullify a pointer	X	X	X	X
Derived-type structure initialization	X	X	X	X
CPU_TIME intrinsic subroutine	X	X	X	X
Kind argument to CEILING and FLOOR intrinsics	X	X	X	X
Nested WHERE constructs, masked ELSEWHERE statement, and named WHERE constructs	X	X	X	X
Comments allowed in namelist input	X	X	X	X
Generic identifier in END INTERFACE statements	X	X	X	X
Minimal FORMAT edit descriptor field width	X	X	X	X
Detection of Obsolescent and/or Deleted features⁶	X	X	X	X

Footnotes to preceding table:

¹	For REAL*16 data, OpenVMS VAX systems use H_float format, and Alpha systems use IEEE style X_float format.
²	For COMPLEX32 data, Alpha systems use IEEE style X_float format for both REAL16 parts.
³	For parallel processing with Compaq Fortran for Compaq Tru64 UNIX Systems, you can use the OpenMP or Compaq Fortran directives on shared memory multiprocessor systems or MPI software for using High Performance Fortran (HPF) constructs across multiple systems.
⁴	For parallel processing, you can use the optional KAP performance preprocessor for a shared memory multiprocessor system.
⁵	BLAS and other routines are available with the Compaq Extended Mathematical Library (CXML) software provided with Compaq Visual Fortran and Compaq Fortran for Alpha systems (for download information, see http://www.compaq.com/math).
⁶	Compaq Fortran flags these deleted and obsolescent features, but fully supports them.

Common Language Extensions

To simplify porting applications between Compaq Fortran 77 Alpha systems and Compaq Fortran (including Compaq Visual Fortran), Compaq Visual Fortran 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
Multiple INTEGER and REAL kinds
Size specifiers for data declaration statements, such as INTEGER*4, in addition to the KIND type parameter
IEEE floating-point data types in memory
The POINTER statement and its associated data type (integer pointers or CRAY pointers).
The typeless PARAMETER statement
The VOLATILE statement
The AUTOMATIC and STATIC statements
Built-in functions used in argument lists, such as %REF, %VAL, and %LOC
Hollerith constants
Variable-format expressions (VFEs)
Certain intrinsic functions
The tab source form (a variation of 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 Visual Fortran also supports the following Compaq Fortran 77 features:

Compaq Fortran 77 compilation control statements and directives, including:
- INCLUDE statement forms using /LIST and /NOLIST (requires compiling with the /vms compiler option )
- 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
foriosdef.for symbolic parameter definitions for use with run-time (IOSTAT) error handling.

Compaq Visual Fortran includes the following features and enhancements also found on other Compaq Fortran platforms:

Support for linking against static libraries
Support for linking against dynamically linked libraries (DLL)
Support for creating code to be put into a dynamically linked library (DLL)
Support for stack-based storage
Support for dynamic memory allocation
Support for reading and writing binary data files in nonnative formats, including IEEE (little-endian and big-endian), VAX, IBM System\360, and CRAY integer and floating point formats
User control over IEEE floating point exception handling, reporting, and resulting values
Control for memory boundary alignment of items in COMMON and fields in structures and warnings for misaligned data
Directives to control listing page titles and subtitles, object file identification field, COMMON and record field alignment, and some attributes of COMMON blocks
Ability to CALL an external function subprogram
7200 character statement length
Free form unlimited line length
Composite data declarations using STRUCTURE, END STRUCTURE, and RECORD statements, and access to record components through field references
Explicit specification of storage allocation units for data types such as:
- INTEGER*4
- LOGICAL*4
- REAL*4
- REAL*8
- COMPLEX*8
Support for 64-bit signed integers using INTEGER*8 and LOGICAL*8
Support for 128-bit floating-point data using REAL*16 and COMPLEX*32 (on Alpha platforms only)
A set of data types:
- BYTE
- LOGICAL*1, LOGICAL*2, LOGICAL*4, LOGICAL*8
- INTEGER*1, INTEGER*2, INTEGER*4, INTEGER*8
- REAL*4, REAL*8
- COMPLEX*8, COMPLEX*16, DOUBLE COMPLEX
Compaq Fortran POINTER statement (CRAY style)
Data statement style initialization in type declaration statements
AUTOMATIC and STATIC statements
Bit constants to initialize LOGICAL, REAL, and INTEGER values and participate in arithmetic and logical expressions
Built-in functions %LOC, %REF, and %VAL
VOLATILE statement
Bit manipulation functions
Binary, hexadecimal, and octal constants and Z and O format edit descriptors applicable to all data types
I/O unit numbers that can be any nonnegative INTEGER*4 value
Variable amounts of data can be read from and written to "STREAM" files, which contain no record delimiters
ENCODE and DECODE statements
ACCEPT, TYPE, and REWRITE input/output statements
DEFINE FILE, UNLOCK, and DELETE statements
USEROPEN subroutine invocation at file OPEN
Support for reading nondelimited character strings as input for character NAMELIST items
Debug statements in source
Generation of a source listing file with optional machine code representation of the executable source
Variable format expressions in a FORMAT statement
Optional run-time bounds checking of array subscripts and character substrings
31-character identifiers that can include dollar sign ($) and underscore (_)
Support for the supercomputer intrinsics POPCNT, POPPAR, LEADZ, and TRAILZ
Language elements that support the various extended range and extended precision floating point architectural features:
- 32-bit IEEE S_floating data type, with an 8-bit exponent and 24-bit mantissa and a precision of typically 7 decimal digits
- 64-bit IEEE T_floating data type, with an 11-bit exponent and 53-bit mantissa and a precision of typically 15 decimal digits
Command line control for:
- The size of default INTEGER, REAL, and DOUBLE PRECISION data items
- The levels and types of optimization to be applied to the program
- The directories to search for INCLUDE and module files
- Inclusion or suppression of various compile-time warnings
- Inclusion or suppression of run-time checking for various I/O and computational errors
- Control over whether compilation terminates after a specific number of errors has been found
- Choosing whether executing code will be thread-reentrant
- Internal procedures can be passed as actual arguments to procedures
Kind types for all of the hardware-supported data types:
- For 1-, 2-, 4-, and 8-byte LOGICAL data: LOGICAL (KIND=1), LOGICAL (KIND=2), LOGICAL (KIND=4), LOGICAL (KIND=8)
- For 1-, 2-, 4-, and 8-byte INTEGER data: INTEGER (KIND=1), INTEGER (KIND=2), INTEGER (KIND=4), INTEGER (KIND=8)
- For 4- and 8-byte REAL data: REAL (KIND=4), REAL (KIND=8)
- For single precision and double precision COMPLEX data: COMPLEX (KIND=4), COMPLEX (KIND=8)

Major Changes to the Fortran Language Standards

Major additions and improvements to the FORTRAN 77 standard introduced by the Fortran 90 standard include:

Array operations and features
Modules
Free-form source
Improved facilities for numeric computation
Parameterized intrinsic data types
User-defined (derived) data types and operators
Generic user-defined procedures
Interface blocks
Pointers (Fortran 90 pointers)
The concept of language evolution
Additional features for source text
Optional procedure arguments
Additional input/output features
Additional control constructs
Additional intrinsic procedures
Additional specification statements
Additional way to specify attributes
Scope and Association

In addition, the Fortran 90 standard includes the following industry-accepted extensions to the FORTRAN 77 standard:

Support for recursive subprograms
IMPLICIT NONE statements
INCLUDE statement
NAMELIST-directed I/O
DO WHILE and ENDDO statements
Use of exclamation point (!) for end of line comments
Support for automatic arrays
Support for the following SELECT CASE – CASE – CASE DEFAULT – END SELECT statements
Support for the EXIT and CYCLE statements and for construct names on DO – END DO statements

Major changes and improvements to the Fortran 90 standard introduced by the Fortran 95 standard include:

The FORALL statement and construct
PURE user-defined procedures
ELEMENTAL user-defined procedures
CPU_TIME intrinsic subroutine
NULL intrinsic function
Derived-type structure default initialization
Pointer initialization
Automatic deallocation of allocatable arrays
Enhanced intrinsic functions, including CEILING, FLOOR, MAXLOC, MINLOC, and SIGN
Printing of -0.0
Enhanced WHERE construct
Generic identifier allowed in END INTERFACE statement
Minimum-length formats
Comments allowed in namelist input

For more information:

See Fortran 95 Features
See Fortran 90 Features

Platform Porting Notes

When porting code between platforms, be aware that:

The use of the /stand option during compilation can help identify source code that uses language extensions during compilation. On U*X Alpha systems, specify the -std option. On OpenVMS systems, specify the /STANDARD qualifier. The online Visual Fortran Language Reference and the printed Compaq Fortran Language Reference Manual identify language extensions with a green-blue color.
The use of certain platform-specific procedures (such as library routines) provided by the operating system need to be located and likely changed. Whenever possible, use Fortran standard language calls (such as to intrinsic procedures) instead of platform-specific routines. For example, if you attempt to link source files and the linker returns unresolved references/symbols, be aware that the routine names may be platform-specific:
- When porting code from a U*X system, identify code that uses system calls (section 2 in reference pages) and certain other library routines not found on Windows systems. Visual Fortran provides the portability library that includes many U*X Fortran library routines (section 3f in reference pages) found on U*X systems. The Compaq Extended Math Library (CXML) routines supported on Alpha systems are provided with Visual Fortran. For more details about the U*X Alpha programming environment, see the appropriate sections in the Compaq Fortran User Manual for Tru64 UNIX and Linux Systems.
- When porting an application from an OpenVMS system, identify code that calls system services (SYS$ prefix) or RTL routines (such prefixes as LIB$, CVT$, DTK$, MATH$, OTS$, PPL$, SMG$, and STR$). The Compaq Extended Math Library (CXML) routines supported on Alpha systems are provided with Visual Fortran.
  Character arguments on OpenVMS systems may be passed by character descriptors not found on other platforms.
  
  For more details about the OpenVMS Alpha programming environment, see the appropriate sections in the Compaq Fortran User Manual for OpenVMS Alpha Systems.
- When porting an application from Visual Fortran to an Alpha system, non-graphical applications are usually easier to port. The nature of Visual Fortran applications is usually defined by the chosen project type (such as Fortran Console applications). For example, applications that use many platform-specific graphical system calls are usually difficult to port to other platforms.
  Certain platform-specific Fortran routine names either have QQ appended at the end of the name or use the Win32 naming conventions (see Calling Win32 Routines). Certain groups of routines require different USE statements. You can use the HTML Help viewer's index and search facility to locate descriptions of Visual Fortran or Win32 routines.
  
  The online Visual Fortran Language Reference and the printed Compaq Fortran Language Reference Manual identify language elements that are supported only on certain Compaq Fortran platforms.
- Certain math library routines provided by Visual Fortran are available on other platforms:
  - The IMSL Math and Statistical routines provided with the Visual Fortran Professional or Enterprise Editions are also available for many other platforms (including Compaq Alpha systems) from Visual Numerics, Inc. (see http://www.vni.com).
  - The Compaq Extended Math Library (CXML) routines provided with all Visual Fortran Editions are also provided with Compaq Fortran on Alpha systems. CXML routines are available separately for Compaq Alpha systems (see http://www.compaq.com/math).
Certain application code may make assumptions about the numeric data format stored in memory. Compaq Fortran and Visual Fortran store numeric data in memory in little endian format, while some vendors use big endian formats. Also, certain platforms support different sized intrinsic data types.
Certain application code may make assumptions about the size of Compaq Fortran (integer) pointers. For example, on an U*X Alpha system, the size of an address is 64 bits. On Windows ia32 systems, the size of an address is 32 bits. On Windows ia64 systems, the size of an address is 64 bits. Whenever possible, use the standard-conforming Fortran 95/90 pointers instead of Compaq Fortran pointers.
Certain platforms use different name decoration conventions, such as appending an extra character to symbol names. Use of the appropriate cDEC$ ATTRIBUTES directives can help overcome this problem (see Adjusting Naming Conventions in Mixed-Language Programming.
Porting data files used by an application from one platform to another. Consider using ftp for binary file transfers to preserve file integrity. Visual Fortran provides the capability to convert unformatted data files in various formats, including big endian formats (see Supported Native and Nonnative Numeric Formats). It is also important to select compatible cross-platform record types.
When porting data files between Windows systems running Compaq Visual Fortran and Alpha systems running Compaq Fortran:
1. For formatted data files, use the stream_LF record type.
2. For unformatted files, use the segmented record type. Unformatted files ported from Compaq Fortran OpenVMS systems may use a non-IEEE floating-point format. For example, Compaq Fortran for OpenVMS Alpha systems allows the user to specify either IEEE and or VAX formats during compilation (see Supported Native and Nonnative Numeric Formats).
One suggested way to port an unformatted file from an OpenVMS system follows:
1. From the OpenVMS system type the following DCL command for the file (file.dat):
```
 $ SET FILE /ATTR=(RFM=FIX,LRL=512) file.dat
```
  For information on porting unformatted data files, see the Compaq Fortran Knowledge Base at http://www.compaq.com/fortran/kb. Examples of record type conversion programs are available at http://www.compaq.com/fortran/examples.
2. Copy the file to your Windows system as a binary (image) copy (perhaps using ftp).
3. Modify the source code to OPEN the file with RECORDTYPE='SEGMEMTED'.
4. If the file uses a VAX floating-point format, specify the appropriate VAX format by using one of the methods described in Converting Unformatted Numeric Data.
Be aware that Fortran-only programs are usually easier to port than mixed-language programs.

For more information:

See the Compatibility appendix and other sections of the appropriate Compaq Fortran for Alpha systems user manual (Compaq Fortran User Manual for Tru64 UNIX and Linux Systems or the Compaq Fortran User Manual for OpenVMS Alpha Systems).