Interfaces

If your subprogram is not in a module you should provide an INTERFACE. The INTERFACE is equivalent to the prototype of some other languages. Interfaces enable the compiler to check that the number and type of the argument list in invocations agrees with the declared parameter list. Interfaces are non-executable and should be placed with (or immediately following) variable declarations.

Syntax

Function

INTERFACE
  FUNCTION myfunc(x,y,z)
     implicit none
     real ::myfunc
     real ::x,y
     complex :: z
  END FUNCTION
END INTERFACE

Subroutine

INTERFACE
  SUBROUTINE mysub(x,y,z)
     use precisions
     use mymod
     implicit none
     real     :: x
     real(dp) ::y,z
  END SUBROUTINE mysub
END INTERFACE

The simplest way to set up an interface is to copy the first lines of the subprogram. All statements that may affect the ability of the compiler to check number and type of the arguments must be included. This encompasses USE (for modules), IMPLICIT, and all declarations of the arguments. Declarations for local variables are not needed and should not be included. The END statements must include the FUNCTION or SUBROUTINE keyword as appropriate.

The interface terminates with END INTERFACE.

Interface Blocks

Only one interface block is required per program unit.

INTERFACE
  function mysub
    declarations
  end function
  subroutine mysub1
    declarations
  end subroutine
  subroutine mysub2
    declarations
  end subroutine
END INTERFACE