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Re: 20030514:Getting ID of an open NetCDF file by its file name

>To: <address@hidden>
>From: "Hernan G. Arango" <address@hidden>
>Subject: Getting ID of an open NetCDF file by its file name
>Organization: UCAR/Unidata
>Keywords: 200305141830.h4EIUKLd024546

Hi Hernan,

> Is there an easy and elegant way of getting the ID of an opened NetCDF
> by specifying its file name?  I am trying to avoid opening too many
> files simultaneously for the same dataset.  I am also trying to avoid
> opening and closing the NetCDF every time that it is needed.  I am using
> this in the context of an ocean model which requires reading input
> NetCDF dataset frequently.

No, unfortunately there is nowhere in the netCDF library where the
association between pathnames and file descriptors (ncids) is stored
for all open files.  For each open file there is an "ncio" structure
that has both the file descriptor and a pointer to the pathname, but
those structs reside in allocated space on the heap, not in an array
or list where they could easily be searched.

So I'm afraid the easiest way for you to do this is to store a table
of ncids and associated pathnames when they are returned from nc_open
or nc_create (or the corresponding F90 interfaces).  One way to do
this would be to write a wrapper for the open, create, and close calls
which calls the appropriate netCDF function and passes back the return
values but also populates a (pathname,ncid) table so you could access
this with another function.  The "close" call would call the netCDF
close function but also delete the associated (pathname,ncid)
association from the table.

This seems like a useful functionality, and something we should add in
the next version of netCDF.  Keeping a data structure with file
descriptors and pathnames would be relatively cheap, but useful in
cases like this.  I'll put it on the list.

--Russ