[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: question for Russ - signed vs. unsigned char and NC_BYTE

> We have both functions so that users can read data into either signed
> or unsigned arrays of char without requiring an ugly cast.  If we only
> had nc_get_att_schar() and a user wanted to read NC_BYTE data into an
> array of unsigned char, they would have to use a cast or get a
> compiler complaint.
> 
But as a user looking at a new file, there's no way for me to tell if
I am dealing with signed or unsigned? I just have to know that in
advance?

Perhaps, someday, we should consider adding a type to netcdf-4 to
allow us to tell the difference?

We are saying, are we not, that NC_CHAR is to be used exclusively for
text strings? Or should that also be used for unsigned char, leaving
NC_BYTE to mean always signed data?

> In either case the same 8 bits are read into the same location in
> memory, but we have to provide both schar and uchar versions to allow
> the user to treat byte data as either signed or unsigned.  No
> conversion takes place reading/writing a signed or unsigned char in
> memory to or from a byte on disk, so users can still treat NC_BYTE
> data as unsigned char if they want to.  To allow them to do this
> without a cast, we provide the convenience function.

I understand that no conversion takes place.

In terms of checking for range errors, as in going from an int to a
NC_BYTE, my understanding was that I treat it as always signed. Is
that right?

> 
> For the same reason, we provide both nc_get_var_schar() and
> nc_get_var_uchar(), and similarly for the corresponding put_var
> functions.

Yes.