William Thompson wrote:
Thomas McGlynn wrote:

The problem is that since the first FITS paper (and still in the
standard),
the fixed format is recommended for header cards. In the fixed format
there
must be at least 8 characters in a character value. Reading that paper
if I wished to specify a string with the value of '' in the fixed format
I believe I would have written it as
ABCDEFGH= ' '
and felt that I was following the recommendations of the standard.


I second this statement. In fact, the FITS-writing software that I use
enforces the fixed format, so that it would be impossible to write a
null string separate from a blank string, e.g.

yes, but ...

I think that's an entirely different question. Some of our older
data reduction software takes offense to character strings containing
nulls, but I consider that beside the point here as well.

I thought the question was whether '' _is_ a null string or a blank
string and I also think that '' should be a null string, independent
of whether we (can) write it or read it, not blank.
We have one case where we would have liked to write a null string,
found that we couldn't do that, and settled on 'none ' (probably
for the better of everybody who reads our data).

IDL fxhmake,h
IDL fxaddpar,h,'abcdefg',''
IDL hprint,h
SIMPLE = T /Written by IDL: Tue Mar 1 11:10:43 2005
BITPIX = 8 /
NAXIS = 0 /
ABCDEFG = ' ' /
END

Aloha,

Maren Purves, UKIRT.