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Re: 20040717: f90 suggestion: optional status code?

>To: address@hidden
>From: Ryo Furue <address@hidden>
>Subject: f90 suggestion: optional status code?
>Organization: University of Hawaii
>Keywords: 200407170841.i6H8fVaW021751 netCDF Fortran90

Hi Ryo,

> Thank you for the wonderful library, which is extremely useful in my
> work.  I'm wondering if I could make a little suggestion for
> possible improvement.
> 
> I'm using the f90 interfaces of netcdf-3.5.1.  I found it very awkward
> to check the status code every time, as in
> 
>     i=nf90_def_dim(id, name = 'longitude', len = nx, dimid = xid)
>     if (i /= nf90_noerror) then
>         write(*,*) trim(nf90_strerror(i))
>         stop 1
>     end if
>     i=nf90_ . . .
>     if (i /= nf90_noerror) then
>         . . . .
> 
> I have nearly thirty calls to netCDF functions in a single short
> program. I know this is a traditional style of the C language.
> But, since we use Fortran 90, which is more powerful than C in this
> respect, we don't need to follow the (awkward) convention of C.
> 
> What's the solution?  We already have a nice answer in the Fortran
> I/O statements (OPEN, READ, etc.).  For example, the OPEN
> statement has an optional argument named "iostat":
> 
>     open(unit = . . ., iostat = ios)
>     if (ios /= 0) then
>         write(*,*) "open error. iostat = ", ios
>         stop 1
>     end if
> 
> But, if you omit iostat when you "call" OPEN and if error occurs,
> then the Fortran runtime system will issue an error message and
> terminates the program.   (I don't know if this is mandated by the
> Fortran 90/95 standard, but most Fortran implementations do this
> anyway.)  On the other hand, if you specify the iostat argument and if
> error occurs, the Fortran runtime remains silent and continues the
> execution of the program.  (I think this continuation is mandated by
> the standard.)  In this case, it's the programmer's responsibility
> to handle (or not handle) the error.  In this way, you can handle
> the error for yourself if you want to, or if you don't, you can let
> the Fortran runtime to take an appropriate action.
> 
> We can mimic this behavior for the netCDF f90 interfaces; e.g.,
> 
>     subroutine nf90s_def_dim(. . . , stat)  ! <-- Not a function.
>        . . . .
>        integer, intent(out), optional:: stat
>        i=nf90_def_dim(. . .)
>        if (present(stat)) then
>           stat = i
>        else if (i /= nf90_noerror) then
>            write(*,*) trim(nf90_strerror(i))
>            clean up and abort; or if the error is not severe
>              we just continue.
>        end if
>     end subroutine nf90s_def_dim
> 
> I could write a set of wrappers myself but there are simply too many
> functions.  If I would write wrappers for myself, I would write them
> only for the small number of functions I use, and so my effort would
> be kind of wasted because the wrappers woudl be used only by me. 
> If, on the other hand, this interface style becomes official, many
> users will be benefited from it.

Thanks for the suggestion.  I've forwarded it to the primary developer
of the Fortran-90 interface, Robert Pincus.  If he agrees that the
benefits of your suggested change would be worth the cost of
implementing and documenting the wrappers, we will consider adding
such wrappers to a future release.

Regards,
--Russ

_____________________________________________________________________

Russ Rew                                         UCAR Unidata Program
address@hidden          http://www.unidata.ucar.edu/staff/russ