Scope of variables in case of modules used by modules in Fortran

Question

I\'ve noticed that variables in a (child) module, which are used by a parent modules are accessible in a main program through just the parent module. This is one concept which c

Answer 1

As Vladimir F suggested in a comment, you can solve this issue using private and public statements in your modules. If you rewrite your modules like this:

module a_mod
  use :: b_mod

  private
  public :: a

  integer :: a
end module

module b_mod
  use :: c_mod

  private
  public :: b

  integer :: b
end module

module c_mod
  private
  public :: c, inc_c

  integer :: c = 10
contains
  subroutine inc_c
    c = c + 10
  end subroutine
end module

In this case, the statement private in the beginning of each module means that quantities declared in the module are not exported by default. You now have to explicitly declare what variables and subroutines to make available when you use the module by adding a public statement. (This could alternatively be done in one line using the syntax integer, public :: c = 10.) This practice prevents c_mod variables from leaking out of b_mod, and so on.