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Re: 20000710: netcdf nc_put_att_text bug?

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  • Subject: Re: 20000710: netcdf nc_put_att_text bug?
  • Date: Mon, 10 Jul 2000 09:01:55 -0600
>From: "Timothy E. Dowling" <address@hidden>
>Subject: netcdf nc_put_att_text bug?
>Organization: ?
>Keywords: 200007101335.e6ADZPT10374 netCDF nc_put_att_text

> I notice that nc_put_att_text(...,len,input string) will
> read past the end of the input string if it is shorter than
> the given len, picking up garbage that it then sends as part
> of the text attribute.  
>
> I think the correct behavior is that it should stop at the
> first '\0' in the input string, and leave the rest of the
> text attribute blank or full of '\0's.

You are making the (reasonable) assumption that netCDF deals with
character array attributes in the form of C strings, properly
terminated with a null '\0' character.  

However netCDF files are language-neutral, so Fortran programs can
read the files too.  There is only a null character terminating a
string attribute if you put it there when you wrote it, and specified
the attribute length (number of characters) to include the extra null
character.  NetCDF permits creating character attributes containing
zero or more null bytes, since some of the languages that read and
write netCDF files have no special interpretation for a null character
(e.g. Fortran).  

Hence it's necessary to use something like

  nc_put_att_text(..., strlen(input_string)+1 ,input_string)

if you want to include the null byte to terminate the string, or

  nc_put_att_text(..., strlen(input_string) ,input_string)

if you want to not include the null byte, since the string length is
available through the netCDF interface without it.

--Russ

_____________________________________________________________________

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