How to use a user-defined-type in a Fortran interface

Question

In a Fortran 2003 module I\'m defining a type called t_savepoint and, later, I want to define an interface for a subroutine called fs_initializesavepoint<

Answer 1

Rightly or wrongly in an interface block you don't have access to the environment by host association. To fix this you need to import the datatype exlicitly:

[luser@cromer stackoverflow]$ cat type.f90
module m_serialization

  implicit none

  type :: t_savepoint
     integer :: savepoint_index
     real    :: savepoint_value
  end type t_savepoint

  interface

     subroutine fs_initializesavepoint(savepoint)
       Import :: t_savepoint
       type(t_savepoint) :: savepoint
     end subroutine fs_initializesavepoint


  end interface

end module m_serialization
[luser@cromer stackoverflow]$ gfortran -c type.f90

This is f2003.

However I suspect the way you have put this suggests you are not going about coding this up the best way. Better is simply to put the routine itself in the module. Then you don't need bother with the interface at all:

module m_serialization

  implicit none

  type :: t_savepoint
     integer :: savepoint_index
     real    :: savepoint_value
  end type t_savepoint

Contains

  Subroutine fs_initializesavepoint(savepoint)

    type(t_savepoint) :: savepoint 

    Write( *, * ) savepoint%savepoint_index, savepoint%savepoint_value

  End Subroutine fs_initializesavepoint

end module m_serialization
[luser@cromer stackoverflow]$ gfortran -c type.f90

Given that modules are really designed to deal with connected entities this is really the way to do it in Fortran. It also has the advantage of only requiring a f95 compiler, so is universally available (though admittedly import is commonly implemented)