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Re: 20010418: unsigned datatypes

>To: address@hidden
>From: address@hidden
>Subject: unsigned datatypes
>Organization: UCAR/Unidata
>Keywords: 200104182010.f3IKAgL10773
     
     
Hi Steven,

>        does netcdf support unsigned datatypes (int, short, char)

No, int and short values are interpreted as signed qualities in
netCDF.  For char or byte values, there is some support for unsigned
data.

Whatever 8-bit byte you store in an NC_BYTE type netCDF variable, you
will get the exact same 8 bits back when you read data from that
netCDF variable into a byte memory location.  If that memory location
is for a variable that's declared "unsigned char", it should be
interpreted as unsigned.

On the other hand, netCDF includes functions that let you read 8-bit
data as other numeric types.  For example, the function

  int nc_get_var_int   (int ncid, int varid, int *ip);

will let you retrieve a variable as an int, whether it's stored as a
byte, a short, an int, a long, a float, or a double.  In that case,
8-bit values are interpreted as signed for the purpose of any numeric
conversions that the library does.  But you can still retrieve the data
as unsigned bytes by using the function:

  int nc_get_vara_uchar (int ncid, int varid, unsigned char *ip);

--Russ

_____________________________________________________________________

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