4.2 Fortran 2008 status

The latest version of the Fortran standard is ISO/IEC 1539-1:2010, informally known as Fortran 2008. The official version is available from International Organization for Standardization (ISO) or its national member organizations. The the final draft (FDIS) can be downloaded free of charge from http://www.nag.co.uk/sc22wg5/links.html. Fortran is developed by the Working Group 5 of Sub-Committee 22 of the Joint Technical Committee 1 of the International Organization for Standardization and the International Electrotechnical Commission (IEC). This group is known as WG5.

The GNU Fortran compiler supports several of the new features of Fortran 2008; the wiki has some information about the current Fortran 2008 implementation status. In particular, the following is implemented.

• The -std=f2008 option and support for the file extensions .f08 and .F08.
• The OPEN statement now supports the NEWUNIT= option, which returns a unique file unit, thus preventing inadvertent use of the same unit in different parts of the program.
• The g0 format descriptor and unlimited format items.
• The mathematical intrinsics ASINH, ACOSH, ATANH, ERF, ERFC, GAMMA, LOG_GAMMA, BESSEL_J0, BESSEL_J1, BESSEL_JN, BESSEL_Y0, BESSEL_Y1, BESSEL_YN, HYPOT, NORM2, and ERFC_SCALED.
• Using complex arguments with TAN, SINH, COSH, TANH, ASIN, ACOS, and ATAN is now possible; ATAN(Y,X) is now an alias for ATAN2(Y,X).
• Support of the PARITY intrinsic functions.
• The following bit intrinsics: LEADZ and TRAILZ for counting the number of leading and trailing zero bits, POPCNT and POPPAR for counting the number of one bits and returning the parity; BGE, BGT, BLE, and BLT for bitwise comparisons; DSHIFTL and DSHIFTR for combined left and right shifts, MASKL and MASKR for simple left and right justified masks, MERGE_BITS for a bitwise merge using a mask, SHIFTA, SHIFTL and SHIFTR for shift operations, and the transformational bit intrinsics IALL, IANY and IPARITY.
• Support of the EXECUTE_COMMAND_LINE intrinsic subroutine.
• Support for the STORAGE_SIZE intrinsic inquiry function.
• The INT{8,16,32} and REAL{32,64,128} kind type parameters and the array-valued named constants INTEGER_KINDS, LOGICAL_KINDS, REAL_KINDS and CHARACTER_KINDS of the intrinsic module ISO_FORTRAN_ENV.
• The module procedures C_SIZEOF of the intrinsic module ISO_C_BINDINGS and COMPILER_VERSION and COMPILER_OPTIONS of ISO_FORTRAN_ENV.
• Coarray support for serial programs with -fcoarray=single flag and experimental support for multiple images with the -fcoarray=lib flag.
• Submodules are supported. It should noted that MODULEs do not produce the smod file needed by the descendent SUBMODULEs unless they contain at least one MODULE PROCEDURE interface. The reason for this is that SUBMODULEs are useless without MODULE PROCEDUREs. See http://j3-fortran.org/doc/meeting/207/15-209.txt for a discussion and a draft interpretation. Adopting this interpretation has the advantage that code that does not use submodules does not generate smod files.
• The DO CONCURRENT construct is supported.
• The BLOCK construct is supported.
• The STOP and the new ERROR STOP statements now support all constant expressions. Both show the signals which were signaling at termination.
• Support for the CONTIGUOUS attribute.
• Support for ALLOCATE with MOLD.
• Support for the IMPURE attribute for procedures, which allows for ELEMENTAL procedures without the restrictions of PURE.
• Null pointers (including NULL()) and not-allocated variables can be used as actual argument to optional non-pointer, non-allocatable dummy arguments, denoting an absent argument.
• Non-pointer variables with TARGET attribute can be used as actual argument to POINTER dummies with INTENT(IN).
• Pointers including procedure pointers and those in a derived type (pointer components) can now be initialized by a target instead of only by NULL.
• The EXIT statement (with construct-name) can be now be used to leave not only the DO but also the ASSOCIATE, BLOCK, IF, SELECT CASE and SELECT TYPE constructs.
• Internal procedures can now be used as actual argument.
• Minor features: obsolesce diagnostics for ENTRY with -std=f2008; a line may start with a semicolon; for internal and module procedures END can be used instead of END SUBROUTINE and END FUNCTION; SELECTED_REAL_KIND now also takes a RADIX argument; intrinsic types are supported for TYPE(intrinsic-type-spec); multiple type-bound procedures can be declared in a single PROCEDURE statement; implied-shape arrays are supported for named constants (PARAMETER).

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