Re: iswxxxxx/towxxxer and Unicode

["Joseph S. Myers" <jsm28 at cam dot ac dot uk>]

On Tue, 18 Jul 2000, Bruno Haible wrote:

> > No.  This means NUL must not be passed to any of these functions.
> 
> The SUSV2 clearly says the contrary. It contains language sufficient
> to conclude that 0x0000 is a valid character and therefore is suitable
> as an argument to iswcntrl:

This can be deduced already from the 1990 C standard (though you need to
go to 1994 for the iswcntrl function):

3.13 multibyte character: A sequence of one or more bytes representing a
member of the extended character set of either the source or the execution
environment.  The extended character set is a superset of the basic
character set.

5.2.1 Character sets: ... A byte with all bits set to 0, called the null
character, shall exist in the basic execution character set; it is used to
terminate a character string literal.

5.2.1.2 Multibyte characters: ... The single-byte characters defined in
5.2.1 shall be present. ... A byte with all bits zero shall be interpreted
as a null character independent of shift state.

7.10.7.2 The mbtowc function: ... It then determines the code for the
value of type wchar_t what corresponds to that multibyte character.  (The
value of the code corresponding to the null character is zero.)

-- 
Joseph S. Myers
jsm28@cam.ac.uk