Private function in Fortran

Question

How do I declare a private function in Fortran?

Answer 1

This will only work with a Fortran 90 module. In your module declaration, you can specify the access limits for a list of variables and routines using the "public" and "private" keywords. I usually find it helpful to use the private keyword by itself initially, which specifies that everything within the module is private unless explicitly marked public.

In the code sample below, subroutine_1() and function_1() are accessible from outside the module via the requisite "use" statement, but any other variable/subroutine/function will be private.

module so_example
  implicit none

  private

  public :: subroutine_1
  public :: function_1

contains

  ! Implementation of subroutines and functions goes here  

end module so_example

Answer 2

If you use modules, here is the syntax:

PUBLIC  :: subname-1, funname-2, ...

PRIVATE :: subname-1, funname-2, ...

All entities listed in PRIVATE will not be accessible from outside of the module and all entities listed in PUBLIC can be accessed from outside of the module. All the others entities, by default, can be accessed from outside of the module.

MODULE  Field
  IMPLICIT   NONE

  Integer :: Dimen

  PUBLIC  :: Gravity
  PRIVATE :: Electric, Magnetic

CONTAINS

  INTEGER FUNCTION  Gravity()
    ..........
  END FUNCTION Gravity


  REAL FUNCTION  Electric()
    ..........
  END FUNCTION


  REAL FUNCTION  Magnetic()
    ..........
  END FUNCTION

  ..........

END MODULE  Field