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simon
Joined: 05 Jul 2006
Posts: 299
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 Posted: Tue May 15, 2012 11:10 am Post subject: Subroutines as optional arguments |
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I am trying to pass the name of a subroutine as an argument to a function, but cannot work out how to avoid a compilation error. I can pass a function as an optional argument, but not a subroutine. In the following code, module m0 defines a function and a subroutine. Modules m1 and m2 then define functions that take an optional function and subroutine, respectively, as arguments. The compiler complains at the definition of s as external, but if s is not optional (and the test for whether s is present is removed) then the program compiles.
Any assistance on what I need to do to get this to work would be greatly appreciated.
| Code: | MODULE m0
CONTAINS
FUNCTION f ()
INTEGER :: f
f=1
RETURN
END FUNCTION f
SUBROUTINE s ()
CONTINUE
RETURN
END SUBROUTINE s
END MODULE m0
MODULE m1
CONTAINS
FUNCTION f1(f)
INTEGER, EXTERNAL, OPTIONAL :: f
IF (PRESENT(f)) THEN
f1=f()
ELSE
f1=0
END IF
RETURN
END FUNCTION f1
END MODULE m1
MODULE m2
CONTAINS
FUNCTION f2(s)
EXTERNAL, OPTIONAL :: s
IF (PRESENT(s)) THEN
CALL s ()
f2=1
ELSE
f2=0
END IF
RETURN
END FUNCTION f2
END MODULE m2
PROGRAM p
USE m0
USE m1
USE m2
i=f1(f)
i=f2(s)
END PROGRAM p
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davidb
Joined: 17 Jul 2009
Posts: 560
Location: UK
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| Posted: Tue May 15, 2012 6:31 pm Post subject: |
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This compiles for me. Write the optional and external declarations as two statements. You can either use external or provide an interface for the subroutine. With the interface block method, the compiler can check if your actual subroutine argument has the correct interface. Also the interface method must be used if aaa and proc are both PURE (I think.)
| Code: |
module foo
contains
function aaa(a, proc)
real, intent(in) :: a
optional :: proc
external :: proc
! Or delete external and enable the following interface block
!interface
! subroutine proc(a)
! real, intent(in) :: a
! end subroutine proc
!end interface
! Make call if proc supplied
if (present(proc)) then
call proc(a)
end if
aaa = 0.0
end function aaa
end module foo
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_________________
Programmer in: Fortran 77/95/2003/2008, C, C++ (& OpenMP), java, Python, Perl |
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JohnCampbell
Joined: 16 Feb 2006
Posts: 2615
Location: Sydney
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| Posted: Thu May 17, 2012 2:45 am Post subject: |
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Can you wrap the subroutine into a function, as with many of the API functions ?
You may still have a problem with the general argument list.
Thinking of a wrapper function, why are all the zzz@ functions written in C and require a C_EXTERNAL definition. Could they have been written in Fortran and contained the C_EXTERNAL definition when calling the WINAPI routine.
Or is it only a direct call to the WINAPI routine, providing a syntax conversion ?
eg: C_EXTERNAL UPDATE_WINDOW@ '__update_window' (VAL)
WINDOW_UPDATE# appears in the .map file, but not __update_window
John |
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