Table of Contents
This document describes those parts of the Fortran 2008 language
which are not in Fortran 2003, and which are now
supported by Release 5.3 of the NAG Fortran Compiler.
Overview of Fortran 2008
The new features of Fortran 2008 that are supported by the NAG Fortran Compiler
can be grouped as follows:
the BLOCK construct,
aditional intrinsic functions for bit manipulation,
miscellaneous and convenience features.
The BLOCK construct
This construct allows declarations of entities within executable code.
tmp = a(i)**3
If (tmp>b(i)) b(i) = tmp
Here the variable tmp has its scope limited to the BLOCK
construct, so will not affect anything outside it.
This is particularly useful when including code by INCLUDE or by
All declarations are allowed within a BLOCK construct except for
COMMON, EQUIVALENCE, IMPLICIT, INTENT,
NAMELIST, OPTIONAL and VALUE; also, statement function
definitions are not permitted.
BLOCK constructs may be nested; like other constructs, branches into a
BLOCK construct from outside are not permitted.
A branch out of a BLOCK construct “completes” execution of the
Entities within a BLOCK construct that do not have the SAVE
attribute (including implicitly via initialisation), will cease to exist when
execution of the construct is completed.
For example, an allocated ALLOCATABLE variable will be automatically
deallocated, and a variable with a FINAL procedure will be finalised.
Additional intrinsic functions for bit manipulation
The elemental intrinsic functions BGE, BGT, BLE and
BLT perform bitwise (i.e. unsigned) comparisons.
They each have two arguments, I and J, which must be of type
Integer but may be of different kind.
The result is default Logical.
For example, BGE(INT(Z'FF',INT8),128) is true, while
INT(Z'FF',INT8)>=128 is false.
The array reduction intrinsic functions IALL, IANY and
IPARITY reduce arrays using bitwise operations.
These are exactly the same as SUM and PRODUCT, except that
instead of reducing the array by the + or * operation, they
reduce it by the IAND, IOR and IEOR intrinsic functions
That it, each element of the result is the bitwise-and, bitwise-or, or
bitwise-exclusive-or of the reduced elements.
If the number of reduced elements is zero, the result is zero for IANY
and IPARITY, and NOT(zero) for IALL.
The elemental intrinsic functions LEADZ and TRAILZ
return the number of leading (most significant) and trailing
(least significant) zero bits in the argument I, which must be of type
Integer (of any kind).
The result is default Integer.
The elemental intrinsic functions MASKL and MASKR
generate simple left-justified and right-justified bitmasks.
The value of MASKL(I,KIND) is an integer with the specified kind that
has its leftmost I bits set to one and the rest set to zero; I
must be non-negative and less than or equal to the bitsize of the result.
If KIND is omitted, the result is default integer.
The value of MASKR is similar, but has its rightmost I bits set
to one instead.
The array reduction intrinsic function PARITY reduces Logical arrays.
It is exactly the same as ALL and ANY, except that instead of
reducing the array by the .AND. or .OR. operation, it reduces it
by the .NEQV. operation.
That is, each element of the result is .TRUE. if an odd number of
reduced elements is .TRUE..
The elemental intrinsic function POPCNT(I) returns the number of bits in
the Integer argument I that are set to 1.
The elemental intrinsic function POPPAR(I) returns zero if the number of
bits in I that are set to 1 are even, and one if it is odd.
The result is default Integer.
The intrinsic module ISO_FORTRAN_ENV contains additional named constants
The additional scalar
integer constants INT8, INT16, INT32, INT64,
REAL32, REAL64 and REAL128 supply the kind type
parameter values for integer and real kinds with the indicated bit sizes.
The additional named array constants CHARACTER_KINDS,
INTEGER_KINDS, LOGICAL_KINDS and REAL_KINDS list the
available kind type parameter values for each type (in no particular order).
Miscellaneous and convenience features
In a structure constructor, the value for an allocatable component may be
omitted: this has the same effect as specifying NULL().
In a STOP statement, the stop-code may be any scalar constant
expression of type integer or default character.
(In the NAG Fortran Compiler this also applies to the PAUSE statement,
but that statement is no longer standard Fortran.)
ENTRY statements are regarded as obsolescent.
An empty internal subprogram part, module subprogram part or type-bound
procedure part is now permitted following a CONTAINS statement.
In the case of the type-bound procedure part, an ineffectual PRIVATE
statement may appear following the unnecessary CONTAINS statement.
A type-bound procedure declaration statement may now declare multiple
type-bound procedures. For example, instead of
PROCEDURE,NOPASS :: a
PROCEDURE,NOPASS :: b=>x
PROCEDURE,NOPASS :: c
the single statement
PROCEDURE,NOPASS :: a, b=>x, c
The NEWUNIT= specifier has been added to the OPEN statement; this
allocates a new unit number that cannot clash with any other logical unit (the
value will be a special negative value).
WRITE(unit,*) 'Logfile opened.'
The NEWUNIT= specifier can only be used if either the FILE=
specifier is also used, or if the STATUS= specifier is used with the
Fortran 2008 extends the rules that are used for generic resolution and for
checking that procedures in a generic are unambiguous.
The new rules are that
a dummy procedure is distinguishable from a dummy variable;
an ALLOCATABLE dummy variable is distinguishable from a POINTER
dummy variable that does not have INTENT(IN).
The Fortran 2008 standard, IS 1539-1:2010(E), is available from ISO as well
as from many national standards bodies.
A number of books describing the new standard are available; the recommended
reference book is
“Modern Fortran Explained” by Metcalf, Reid & Cohen,
Oxford University Press, 2011 (ISBN 978-0-19-960141-7).