Re: 19991115: Basic NetCDFperl question: character arrays

Mahesh,

> To: address@hidden
> cc: address@hidden
> From: address@hidden (Krishnan Mahesh)
> Subject: Basic NetCDFperl question
> Organization: .
> Keywords: 199911182048.NAA16825

In the above message, you wrote:

> I am a new user of netCDF perl, and have a potentially silly  
> question.

Your question isn't silly at all.

> I have an array of characters, e.g.
> @names = ("this", "is", "a", "test") 
> 
> that i am trying to write to a NetCDF file.
> I have tried a variety of things, none of which worked. The only  
> things that i did manage to get working is to have a seprate id for  
> each element of the array, break up each element into an array of
> characters, and then varput the array.

Basically, the netCDF libraray treats strings as an array of characters
while Perl treats strings as scalars.  This causes problems when reading
and writing string variables.

I found the enclosed email in the netCDF-perl archive.  I hope it
helps.

> Krishnan Mahesh
> Stanford University

--------
Steve Emmerson   <http://www.unidata.ucar.edu>

From address@hidden  Fri Nov 12 08:57:18 1999
        by unidata.ucar.edu (8.8.8/8.8.8) with SMTP id IAA23133;
        Fri, 12 Nov 1999 08:57:17 -0700 (MST)
Message-Id: <address@hidden>
To: Steve Diggs <address@hidden>
cc: address@hidden
Subject: Re: problems with Perl/NetCDF 
In-reply-to: Your message of "Thu, 11 Nov 1999 16:28:20 PST."
Date: Fri, 12 Nov 1999 08:57:20 -0700
From: Steve Emmerson <address@hidden>

Steve,

>Date: Thu, 11 Nov 1999 16:28:20 -0800 (PST)
>From: Steve Diggs <address@hidden>
>Organization: Scripps Institution of Oceanography
>To: address@hidden
>Subject: problems with Perl/NetCDF
>Keywords: 199911120028.RAA27258

In the above message, you wrote:

> This may be a boneheaded question,but isthere something special that I need
> to do in the Perl/NetCDF interface to store and retrieve CHAR-type
> variables.

Basically, the Perl script has to convert the individual integral values
into characters and concatenate them together.

I know, it's a pain.

> I'm getting the decimal values back when I retreive the variables stored as
> NetCDF::CHAR.
> 
> Any pointers to *extensive* and simplistic documentation for the
> NetCDF-Perl interface would be much appreciated as would any analysis of
> swhat I'm doing wrong.  I've included codelets of the writing and reading
> routines. BTW, ncdump correctly dumps the variables, but I can't get the
> Perl script to return the ASCII version of the stored variables.
> 
> -Steve Diggs
> --
> --------------------------------------------------------------------
> Steve Diggs                                   Voice: (619)534-1108
> Scripps Institution of Oceanography           FAX  : (619)534-7383
> WOCE Hydrographic Program Office/STS          EMAIL: address@hidden
> 9500 Gilman Drive                             WWW  : whpo.ucsd.edu
> La Jolla, CA 92093-0214
> --------------------------------------------------------------------

I'm not a Perl expert -- but one of my colleagues is.  He wrote the
enclosed example, which I found in the netcdf-perl support-mail archive
by searching for the string "string".  I believe you'll find what you're
looking for near the end of the example.

Please let me know if this helps.

--------
Steve Emmerson   <http://www.unidata.ucar.edu>

--------Example:
Date: Tue, 4 Mar 1997 12:42:23 -0700 (MST)
From: Robb Kambic <address@hidden>
To: Mitch Baltuch <address@hidden>
cc: address@hidden, address@hidden
Subject: again, bad for loop last time


#!/usr/local/bin/perl
#
#  Example on reading strings from a NetCDF file using netcdf-perl interface
#  Using a metar NetCDF file
#
#
use NetCDF ;

# process input parameters
if( $#ARGV == 0 ) {
        $ncfile = $ARGV[ 0 ] ;
} else {
        die "Wrong number of parameters " ;
}
# set error handling to verbose only
$result = NetCDF::opts( VERBOSE ) ;

# open or create ncfiles
if( -e $ncfile ) {
        $ncid = NetCDF::open( "$ncfile", RDWR ) ;

        # get value of dimension recNum in variable $recnum
        $recNum_id = NetCDF::dimid( $ncid, "recNum" ) ;
        $name_id =  "xxxxxxxx"  ;
        $recnum =  -1  ;
        NetCDF::diminq( $ncid, $recNum_id, $name_id, $recnum ) ;

        if( $recnum > 0 ) {

                # where to start getting info
                @start = ( 0 ) ;

                # get value of dimension stn_name_len in $stn_name_len
                $stn_name_len_id = NetCDF::dimid( $ncid, "stn_name_len" ) ;
                NetCDF::diminq( $ncid, $stn_name_len_id, $name_id, 
                        $stn_name_len ) ;

                # How much to read
                @count = ( $recnum, $stn_name_len ) ;  

                # Initialize array to read into
                $StrLen = "\0" x $stn_name_len ;
                @STNS = ( $StrLen ) x ( $recnum ) ;

                # get id of variable stn_name in stn_name_id
                $stn_name_id = NetCDF::varid( $ncid, "stn_name" ) ;

                # read stations into @STNS array
                NetCDF::varget( $ncid, $stn_name_id, \@start, \@count, 
                                \@STNS ) ;

                # NetCDF treats strings as arrays, perl treats string as
                # scalars, so convert arrays to scalars for perl
                for( $i = 0; $i <= $#STNS; $i += 4 ) {
                        for( $j = $i; $j < ( $i + $stn_name_len ); $j++ ) {
                                $station .= chr( $STNS[ $j ] ) ;
                        }
                        print "Station = $station\n" ;
                        undef( $station ) ;
                }
        }
        $result = NetCDF::close( $ncid ) ;
} else {
        print "Can't find input file $ncfile\n" ;
        exit 0 ;
}
exit 0 ;


_______________________________________________________________________________
Robb Kambic                                Unidata Program Center
Software Engineer                          Univ. Corp for Atmospheric Research
address@hidden             WWW: http://www.unidata.ucar.edu/
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