CODEWITHSUNDEEP
fortran
xebtl
xebtl

Reputation: 490

Statement labels in wrapper functions

In Fortran, is there a way to pass a statement label through a wrapper function?

To elaborate, I am writing a wrapper for open(), like so:

program test                                                                          
contains                                                                              
  subroutine my_open(unit, file, err)                                                 
    integer,      intent(in)           :: unit                                        
    character(*), intent(in)           :: file                                        
    integer,      intent(in), optional :: err                                         

    if (present(err)) then                                                            
       open(unit, FILE=file, ERR=err)                                                 
    else                                                                              
       open(unit, FILE=file)                                                          
    end if                                                                            
  end subroutine my_open                                                              
end program test

(of course my actual procedure contains more logic …). But gfortran complains

       open(unit, FILE=file, ERR=err)                                                 
                                 1                                                    
Error: Invalid value for ERR specification at (1)

Is there a way to do this?

Upvotes: 3

Views: 225

Answers (1)

francescalus
francescalus

Reputation: 32451

The label corresponding to err has to be a label in the scoping unit of the open. So what you want to do isn't possible. Also, to answer your more general question, passing labels as variable isn't possible in itself (at least, since Fortran 95 which deleted assigned formats and gotos).

However, for the specific case, using iostat instead, and passing control back to the calling subprogram is possible.

Something like (simplified):

call my_open(12, file, status)
! Instead of:
! 10 STOP
if (status.ne.0) then
!...
end if

end

subroutine my_open(unit, file, status)
   integer, intent(in) :: unit
   character(*), intent(in) ::file
   integer, intent(out) :: status

   open(unit, file=file, iostat=status)
   if (iostat.ne.0) return
end subroutine

This is arguably much better than having what would essentially be a goto to a very different part of the code from the subroutine. [err isn't popular at the best of times.] Further, this status-passing can be generalized to other cases where you would want to pass labels.

Upvotes: 4

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