Re: ncdigest V1 #887: Reserving header space and use of double underbar tuning functions

• To: <Harvey.Davies@xxxxxxxx>
• Subject: Re: ncdigest V1 #887: Reserving header space and use of double underbar tuning functions
• From: Ed Hartnett <ed@xxxxxxxxxxxxxxxx>
• Date: Sun, 17 Jul 2005 22:21:43 -0600

<Harvey.Davies@xxxxxxxx> writes:

> There was discussion in ncdigest V1 #887 on reserving header space using
> the double underbar tuning function nc__enddef.
>
> I believe there is a need to:
>
> 1. Clarify the status of the three double underbar tuning functions
> nc__create, nc__open and nc__enddef
>
> 2. Make clearer recommendations about their use.
>
> The NetCDF C Interface Guide contains section 2.10 headed
> "Leave Define Mode with Performance Tuning: nc__enddef" with URL
> http://my.unidata.ucar.edu/content/software/netcdf/docs/netcdf-c/nc_005f
> _005fenddef.html#nc_005f_005fenddef
> This section contains the following warning paragraph:
>
> Caution: this function exposes internals of the netcdf version 1 file
> format. Users should use nc_enddef in most circumstances. This function
> may not be available on future netcdf implementations.
>
> Does this warning apply to all three tuning functions?
>
> Are these functions supported by
> 1. OPeNDAP (DODS)
> 2. netCDF-4?

Howdy Harvey!

You raise some great questions, and I can't wait to see Russ's
answers!

One question I can answer: the netCDF-4 one.

In netcdf-4 the functions are supported, but they behave identically
to their single-underscore counterparts. That is, the extra tuning
parameters are ignored on netCDF-4 files.

So if you have an existing program that uses the tuning functions, and
you want to switch the program to netCDF-4, it's not necessary to
replace the calls with their single-underscore counterparts, but there
is no tuning either.

(Also note that one doesn't have to call nc_enddef in netCDF-4 - it
will be called automatically, when needed).

Thanks,

Ed

-- 
Ed Hartnett  -- ed@xxxxxxxxxxxxxxxx

• References:
  • RE: ncdigest V1 #887: Reserving header space and use of double underbar tuning functions
    • From: Harvey.Davies