C/C++ and Fortran

Originally posted by: Ka_Lin

Authors: Ka Lin, Daniel Chen

A submodule extends a module or another submodule. It can also have its descendant submodules. You can declare a module procedure interface body in a module and define it in one of the descendant submodules. A submodule access entities in its ancestor module or submodules through host association.

Here is an example:

MODULE m             ! The ancestor module m             
 
  INTEGER :: i
 
  ! Two module procedure interface bodies, sub1 and sub2, are declared in module m.
 
  INTERFACE
    MODULE SUBROUTINE sub1(arg1)          ! Module procedure interface body for sub1
      INTEGER :: arg1
    END SUBROUTINE
    
    MODULE SUBROUTINE sub2(arg2)          ! Module procedure interface body for sub2
      INTEGER :: arg2
    END SUBROUTINE
  END INTERFACE
END MODULE


SUBMODULE (m) n         ! Submodule n that extends module m.
  INTEGER :: j             

  INTERFACE
    MODULE SUBROUTINE sub3(arg3)          ! Module procedure interface body for sub3
      INTEGER :: arg3
    END SUBROUTINE
  END INTERFACE

  CONTAINS

    ! Module procedure interface body sub1 is defined as follows in submodule n."
               
    MODULE SUBROUTINE sub1(arg1)
      INTEGER :: arg 1
      arg1 = 1
      i = 2                       ! i declared in module m is accessed by host association.
      j = 3                       ! Host association
    END SUBROUTINE

    ! You can also define a module procedure interface body using the module procedure subprogram
    ! statement that allows you to omit the argument list and the function result type if the module
    ! procedure is a function.

    ! Module procedure interface body sub2 is defined using the module procedure subprogram statement
    ! as follows in submodule n.

    MODULE PROCEDURE sub2
      arg2 = 1
    END PROCEDURE
END SUBMODULE


SUBMODULE (m:n) p     ! Submodule p that extends the parent submodule n.
  INTEGER :: k             

  CONTAINS

    ! Module procedure interface body sub3 is defined as follows in submodule p.
               
    MODULE SUBROUTINE sub3(arg3)
      INTEGER :: arg 3
      arg3 = 3
      k = 4                               ! Host association
    END SUBROUTINE

END SUBMODULE

For syntax details and rules of a submodule, see:
http://www.ibm.com/support/knowledgecenter/SSAT4T_15.1.0/com.ibm.xlf151.linux.doc/language_ref/submodules.html