[GRASS5] How to code NULL in sites lists?

[Eric G . Miller]

On Wed, Oct 11, 2000 at 04:18:55PM +0100, Markus Neteler wrote:
> Hi all,
> 
> I just don't know how to code NULL in a sites list with
> floating point data...
> 
> Example:
> 
> 3570018.250000|5766419.000000|-35|%0.86
> 3570018.250000|5766419.000000|-45|%1.04
> 3570018.250000|5766419.000000|-110|%*
>                                    ^^ this shall be no data.
> 
> Is that correct?

Yes, but how will code check for any NULL attribute?  I don't think the
current library functions will allow NULLs for any attribute.  It's
probably a good idea to allow, but library functions will have to be
modified (not to mention modules).  Can we rely on using NAN to indicate
a NULL value for a double and a zero-length string for NULL string
attributes?  I know there are problems using NAN on older systems.

Still, I think we should allow it, since it's completely logical that a
site may not have a value for a particular attribute while others do.
If the library functions are modified, I don't think we need to
introduce yet another special character into the site_list file format.
Simply having the metacharacter followed by a space should be enough to
flag a NULL attribute.  The library functions need to be taught that
this is okay.

3567.1234|1234.567|#1 % %234.45 @"my label" @"alt name"
12345.009|1254.234|#2 %23.54 %22.123 @"the label" @ 


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