- adjustable array
The array in a subprogram
has a variable dimension just as in Fortran 77 through that both the
array name and the dimension (all dimensions) are dummy arguments. The actual
shape is therefore passed from the actual arguments.
SUBROUTINE SUB (A, NA)
REAL, DIMENSION (NA) :: A
- allocatable array
An array specified as
ALLOCATABLE with a certain type and rank.
It can later be allocated a certain extent with
the ALLOCATE statement. The corresponding
storage area can be released with the DEALLOCATE statement.
Dimensioned quantity (variable or constant).
- array assignment
Assignment of a whole
array to another one is permitted provided they have the same
shape, and also if the expression on the right
hand side is a scalar, in which case all the elements on the left
hand side will be assigned this same value.
Array sections can be used here instead
- array function
A function which operates
on an array and returns an array or a scalar, or a function
which operates on a scalar and returns an array. An array valued
function is an array function which returns an array.
- array section
Part of an array (the part
can have a rank greater than one, but array sections with
rank one are the most common cases).
- assumed-shape array
An array in a
subprogram which is not local and has a certain data type and a certain
SUBROUTINE SUB (A)
REAL, DIMENSION (:, :, :) :: A
The extent is determined from an explicit
INTERFACE in the calling program unit, and an explicit
specification of the shape of A there
(including the extent).
SUBROUTINE SUB (A)
REAL, DIMENSION (:, :, :) :: A
END SUBROUTINE SUB
- assumed-size array
The array has a variable dimension, like in
Fortran 77, through that both the array name
and the parameters of the dimension are
dummy arguments, except the last dimension,
which is given by a *
SUBROUTINE SUB (A, NA1, NA2)
REAL, DIMENSION (NA1, NA2,*) :: A
In Fortran 66 the concept "assumed-size array" was not defined, but it was simulated
by placing the digit "1" where the "*" is in Fortran 77. This custom violates the
index check and is of course forbidden by modern compilers, for example the
NAG Fortran 90 compiler. Many old programs still use this way of simulating dynamic memory allocation.
At the specification of a
variable the additional properties PARAMETER,
PUBLIC, PRIVATE, INTENT, DIMENSION,
SAVE, OPTIONAL, POINTER, TARGET,
are called attributes. They can also
be given by statements.
- automatic array
Array in a subprogram where the array is
local but the parameters for the dimensions
are among the dummy arguments.
SUBROUTINE SUB (I, J, K)
REAL, DIMENSION (I, J, K) :: X
- BLOCK DATA
A BLOCK DATA
program unit contains definitions (initial values) which are
to be used in the other program units.
BLOCK DATA is now being replaced with the
more powerful module.
- deferred-shape array
The array is an array pointer or an
The number of elements along the
The functions and subroutines you write
or obtain from application libraries.
The opposite is INTRINSIC.
When external functions or subroutines
are used as actual parameters at the reference
of another subprogram they have to be
specified as EXTERNAL.
A program unit which returns a function value
(or several, if array valued) in its name
and has a number of arguments. Functions
without arguments are permitted, it is also
permitted but not advisable that a
function changes any of its arguments.
A generic function can have the property
that the data type of the argument gives
the same data type to the function. The value
SIN(1.0D0) is also more accurate (calculated
to a higher precision) than that of
In addition, there exist intrinsic functions,
for example REAL() which can have arguments
of various data types, but always returns a
value of a certain data type. For generic
subroutines only the arguments are adjusted.
Since all the different program units in a
Fortran program are compiled completely
independent all information on the arguments
have to be transferred manually. In
this was done with very long and cumbersome
In Fortran 90 an INTERFACE
can be used. This has to be used in the
- modules that use user defined data types
- call with keyword arguments or optional arguments
- user defined generic routines
- use of assumed-shape arrays
- use of arrays specified with pointers
- at the definition of a new interpretation of an OPERATOR
- to increase the chance that INTENT has any effect
(implementation dependent case)
- call of an array valued function
- If IMPLICIT NONE is being used, an INTERFACE may be
required at the use of a subprogram as the actual argument
- internal function
A function which is local to a certain
program unit, and is after a
statement. All the variables in the
program unit are directly available.
An internal function can not be used
outside the program unit where it is defined.
This can be useful in order to avoid
name conflicts between functions and
subroutines from different libraries.
An internal function can not be used as
an argument! It also exists internal
Those functions and subroutines that are
delivered together with the compiler are
called intrinsic, and have some special
properties, they do not usually have to
be specified. Since Fortran 90 has so
many intrinsic functions, some manufacturers
may choose to let some of them instead be
available in a usual library, and thus be
The opposite to intrinsic is external.
If intrinsic functions or subroutines
are used as arguments at the call of
some other subprogram they must be
specified as INTRINSIC. Note the very
important difference between an intrinsic
and an internal subprogram.
With a loop we mean a number of executable
statements that are repeated a number of
the usual case is a DO-loop, but also an
IF-statement (arithmetic or logical or the
newer IF...THEN...ELSE...ENDIF or
construct can be called a loop.
- main program
Each Fortran program has to consist
of exactly one main program and and any number of
BLOCK DATA program units.
A main program may start with the statement PROGRAM name
and must be terminated with a statement END PROGRAM name
or END PROGRAM or the simpler END
A module contains specifications and
definitions to be used in other program
units. Replaces BLOCK DATA.
Inside a DO-loop can be
further DO-loops, inside an IF...THEN...ELSE...ENDIF or
CASE can also be additional constructs.
Sometimes also IF and CASE constructs
are called loops.
- program unit
The collective reference to a
main program, a subroutine,
a function, a module or a
BLOCK DATA program unit.
The number of dimensions.
WARNING: Not the mathematical rank.
A function or a subroutine that calls itself.
Permitted from Fortran 90.
- result variable
A function is called by its
function name, and on return that name contains the value
of the function. If the function is recursive
a special result variable has to be used
inside the function in order to store the
temporarily, but it is still returned in the
usual way via the function name.
The result variable is also useful for
array functions, even in the non-recursive
It is always permitted in a function
specification to use the result variable.
The shape of an array consists of its
rank and extent.
- statement function
A function local to
a program unit, is located between the ordinary specifications
and the executable statements. Very simple, available already in FORTRAN I.
A more general concept is the internal function
after a CONTAINS statement. A statement
function may not be used as an argument!
A program unit which does not return any
value through its name and has a number
It is permitted for a subroutine to change
the values of its arguments. A subroutine
can however have other tasks to perform,
quite often related to input and output.
A subroutine does not have a data type.