fortran - What are the ways to pass a set of variable values through the subroutine to a function without common block?

Question

I do not want to use common blocks in my program. My main program calls a subroutine which calls a function. The function needs variables from the subroutine.

What are the ways to pass the set of information from the subroutine to the function?

program
...

call CONDAT(i,j)

end program

SUBROUTINE CONDAT(i,j)

common /contact/ iab11,iab22,xx2,yy2,zz2
common /ellip/ b1,c1,f1,g1,h1,d1,b2,c2,f2,g2,h2,p2,q2,r2,d2
call function f(x)
RETURN
END

function f(x)
common /contact/ iab11,iab22,xx2,yy2,zz2
common /ellip/ b1,c1,f1,g1,h1,d1,b2,c2,f2,g2,h2,p2,q2,r2,d2
end

Answer 1

What you care about here is association: you want to be able to associate entities in the function f with those in the subroutine condat. Storage association is one way to do this, which is what the common block is doing.

There are other forms of association which can be useful. These are

• use association
• host association
• argument association

Argument association is described in haraldkl's answer.

Use association comes through modules like

module global_variables
  implicit none     ! I'm guessing on declarations, but that's not important
  public   ! Which is the default
  real b1,c1,f1,g1,h1,d1,b2,c2,f2,g2,h2,p2,q2,r2,d2,xx2,yy2,zz2
  integer iab11,iab22
end module

subroutine condat(i,j)
  use global_variables   ! Those public things are use associated
  ...
end subroutine

function f(x)
  use global_variables   ! And the same entities are accessible here
  ...
end function

Host association is having access to entities accessible to the host. A host here could usefully be a module or a program

module everything
  integer iab11,...
  real ...
 contains
  subroutine condat(i,j)
    ! iab11 available from the host module
  end subroutine

  function f(x)
    ! iab11 available from the host module
  end function
end module

or even the subroutine itself

subroutine condat(i,j)
  integer iab11,...
  real ...
 contains
  function f(x)
    ! Host condat's iab11 is accessible here
  end function
 end subroutine