This document introduces some new concepts available in Fortran 90-2003 compared to Fortran 77, including: 1) Free format source code which removes the need for fixed column formatting. 2) New data types like assumed shape arrays which provide meta information about array dimensions, allowing whole array operations. 3) Modules which group functionality and avoid name clashes by hiding implementation details. 4) Interface blocks which enable operator and function overloading. 5) C-binding features which allow mixing Fortran and C code by controlling argument passing and data translation between the languages.

1. Introduction to “modern” Fortran
Nils van Velzen
May 2016 1

2. Before we start:
• +65 years old
• FORTRAN 66, FORTRAN 77, Fortran 90,
Fortran 95 en Fortran 2003
• Create awareness of some “new” concepts
available in Fortran90 – 2003
• Selection of relevant topics (understatement)
• Code examples

3. Topics
• Free format source
• Data types
• Modules and interfacing (overloading)
• C-Binding (Fortran 2003)

4. Free format source
Fixed format in fortran77
• 1-5: label
• 6: continuation
• 7-72 code

5. Free format source
• No fixed columns
• Longer names of variables, functions etc. (max 63 char)

6. Data in F90+
arrays
Arrays in fortran90+ are different from those in F77

7. Data in F90+
arrays in F90 and F77
F90: Assumed shape arrays (:), (:,:)
F77: Assumed size arrays (*) and (n,*) etc
F90: Meta information provided with variable
F77: just a memory address
F77+F90: Explicit declaration (n) and (n,m)
NOTE1: Explicit interfacing is needed for a routine accepting
(F90) assumed shape arrays
NOTE2: Compiler assumes (F77) assumed size arrays when
interface is not provided
Assumed shape èAssumed size (no problem)
Assumed size èAssumed shape (we can do this in F2003)

8. Data in F90+
whole array operations
Examples: Suppose a, b, c are real arrays, q logical array.
• c = a + b element-by-element addition.
• b = a / 2.0 all elements divided by 2.0.
• a = exp( b) function appliedto each element.
• q = c > 0 q(i) true if c(i) > 0.
• a=1.0 Set all array element to 1.0
Whole array operations allowed with intrinsic types, intrinsic
operations and elemental intrinsic functions.
Element-by-element execution in arbitrary order.
Arrays must be conformable.

9. Data in F90+
Arrays: some definitions
Rank of an array = number of dimensions.
Extent of a dimension = number of elements in that dimension.
Size of an array = total number of elements (product of extents).
Shape of an array = 1-dim integer array: extents of all dimensions
Shape of an array is characterisedby its rank and the extents of each of its
dimensions.
Two arrays are conformable if they have the same shape.
A scalar is conformable with all shapes of arrays.
Examples:
real :: A1(1), A2(1,1), A3(1,1,1) ! All different shapes.
real :: A(1:4), B(0:3) ! Same shape.

10. 1 6 11 16
2 7 12 17
3 8 13 18
4 9 14 19
5 10 15 20
Data in F90+
Arrays: selectionsExamples:
x(1:n) elements 1 .. n
buf(0:100:2) elements with index 0, 2, 4, ..., 100
A( i, : ) row i of matrixA
Subscript triplet
General: istart:iend:stride
Short forms: istart:iend istart: :iend :
Example of equal shapes
Arrays declared as a(1:5,1:4), b(-1:1,0:3), c(3,4)
Result of c = a(1:5:2,:) + b(:,3:0:-1)
0.1 0.4 0.7 0.10
0.2 0.5 0.8 0.11
0.3 0.6 0.9 0.12
1.10 6.7 11.4 16.1
3.11 8.8 13.5 18.2
5.12 10.9 15.6 20.3
a b c

11. Data in F90+
Allocatable (arrays)

12. Data in F90+
Allocatable (arrays)
Allocate wherever you want
Error when you allocate an allocated array
Automatic deallocation when out of scope
Note “save” attribute means never out of scope
Check allocation [de]allocate(<list>,stat=<variable>)
Allocation status: allocated or not allocated.
Declared in a module: autom. dealloc. platform dependent.

13. Data in F90+Types

14. Data in F90+
Pointer attribute

15. Data in F90+
Pointer attribute
Declare without bounds:
Allocation/deallocation like “allocatable”
2-nd allocation: no crash possible memory leak.
error when not pointingto allocatedmemory
Set pointer explicitly to “null”
Redirect pointer to other pointer or variable with “target”
attribute
Behaves like normal (Fortran) variable unlike C pointers
Check association associated(A) or associated(A,B)
real, pointer :: A(:,:), B(:,:), Y(:)
real, target ::Z(10)
Y=>Z(5:9)
A=>B
nullify(A)
A=>null()

16. Modules
Group functionality; mini library; hiding
Alternative for common blocks
Generation of .mod file (binary file)
Mod files are compiler specific
No circular usage(!)
Good for performance (?)
Pitfall: accidental introduction of recursion while
developing

17. Modules:
USE statementTwo forms:
use module-name [,name-as-used=>name-in-module]...
use module-name, only: [only-list]
only-list: names in module and rename clauses as above.
Compilation order: module before referencing program.
Example: program TPLMOD
use PLMOD
implicit none
integer :: IEOF
real :: XC, YC
call PLINI
do
read(*,*,iostat=IEOF) XC, YC
if( IEOF /= 0) exit
call PLADD( XC, YC)
end do
call PLWRI( 6)
end program TPLMOD

18. Interface
No interface needed
callingF77

19. Interface:
Overloading

20. Interface:
Operator overloading

22. C-binding
• Binding with other languages part of the
Fortran2003 standard
• Kind definitions for C data types
• Control over routine name in library
• Control of argument parsing (val/ref)
• Translation of c data arrays, structs, function
to Fortran counterparts and back

23. C-binding

24. C-binding

25. C-binding

26. C-binding
gfortran -c example16_mod.f90 -o mul.o
gcc example16.c mul.o –lgfortran
Note: fortran runtime library

27. C-binding

28. Object Oriented programming