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Re: 20040703: Some NetCDF C interface doc issues (cont.) (fwd)

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Date:    Mon, 12 Jul 2004 09:50:34 -0600
From:    Russ Rew <address@hidden>
To:      der Mouse <address@hidden>
cc:      ed
Subject: Re: 20040703: Some NetCDF C interface doc issues (cont.) 

>To: address@hidden
>From: der Mouse <address@hidden>
>Subject: Some NetCDF C interface doc issues
>Organization: ?
>Keywords: 200407030332.i633WhaW006446

Hi der Mouse,

> * All the nc_put_var1_* functions take pointers to the data to store.
>   This makes no sense to me; why not simply pass the datum directly
>   rather than forcing the caller to allocate a variable to store it?

Ed responded to many of your suggestions on the documentation, and you
wrote back:

> > Or am I reading your question wrong?  Do you really want to do
> > something like this?
> 
> > nc_put_var1_int(ncid, varid, index, 99);
> 
> Exactly.  (Mutatis mutandis, that is.  See below.)
> 
> > If so, you're right, that won't work.  However it seems like few
> > programs would be writing a data constant with nc_put_var1_int.
> 
> Oh, the last arg doesn't have to be a constant, and in the case at hand
> it wasn't.  I wanted to do
> 
> nc_put_var1_float(dsid,v_load,&locv[0],int1/(float)int2);
> 
> but instead I had to allocate a variable, otherwise unused, to hold the
> quotient.  Thing is, I can't see anything that using a pointer allows
> you to do that you can't do at least as well without the pointer, which
> leaves me rather baffled about why you designed it that way.  Either
> I'm missing something or you did something gratuitously bizarre, and
> either way, I'm puzzled.

Now that I'm back from vacation, I wanted to offer an
explanation/excuse for the interface you are referring to here, since
I was one of the four developers who agreed to it.

This was done to make the interface simple and consistent, since all
the other C functions for putting or getting data take pointers to the
data.  It was a trade-off between making the interface consistent
enough to be easy to remember and making each function call as simple
as possible.  With the current interface, writing a single array value
with the nc_put_vara_* functions is very similar to writing a single
value with the nc_put_var1_* functions, and similar to writing or
reading array slices with other functions.  I agree with you that this
seems awkward (or maybe even "gratuitously bizarre") if you use the
nc_put_var1_* functions a lot, but giving a name to something you put
in an argument list is also helpful to later maintainers, as in:

  {
     double rh_value = int1/(float)int2;
     status = nc_put_var1_double(ncid, rh_id, rh_index, &rh_value);
  }

and the current interface encourages this, although that's not its
primary intention.  But again, I agree that this is a pretty weak
argument for an arguably bad interface, which it's now too late to
change ...

--Russ



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