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    CWG Issue 1796</TITLE>
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<P><EM>This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21
  Core Issues List revision 118b.
  See http://www.open-std.org/jtc1/sc22/wg21/ for the official
  list.</EM></P>
<P>2025-09-28</P>
<HR>
<A NAME="1796"></A><H4>1796.
  
Is all-bits-zero for null characters a meaningful requirement?
</H4>
<B>Section: </B>5.3.1&#160; [<A href="https://wg21.link/lex.charset">lex.charset</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD4
 &#160;&#160;&#160;

 <B>Submitter: </B>Tony van Eerd
 &#160;&#160;&#160;

 <B>Date: </B>2013-10-02<BR>


<P>[Moved to DR at the November, 2014 meeting.]</P>



<P>According to 5.3.1 [<A href="https://wg21.link/lex.charset#3">lex.charset</A>] paragraph 3,</P>

<BLOCKQUOTE>

The <I>basic execution character set</I> and the <I>basic execution
wide-character set</I> shall each contain all the members of the
basic source character set, plus control characters
representing alert, backspace, and carriage return, plus a
<I>null character</I> (respectively, <I>null wide
character</I>), whose representation has all zero bits.

</BLOCKQUOTE>

<P>It is not clear that a portable program can examine the bits
of the representation; instead, it would appear to be limited to
examining the bits of the numbers corresponding to the value
representation (6.9.2 [<A href="https://wg21.link/basic.fundamental#1">basic.fundamental</A>] paragraph 1).  It might
be more appropriate to require that the null character value compare
equal to 0 or <TT>'\0'</TT> rather than specifying the bit pattern
of the representation.</P>

<P>There is a similar issue for the definition of shift, bitwise
<TT>and</TT>, and bitwise <TT>or</TT> operators: are those
specifications constraints on the bit pattern of the representation
or on the values resulting from the interpretation of those patterns
as numbers?</P>

<P><B>Proposed resolution (February, 2014):</B></P>

<P>Change 5.3.1 [<A href="https://wg21.link/lex.charset#3">lex.charset</A>] paragraph 3 as follows:</P>

<BLOCKQUOTE>

The <I>basic execution character set</I> and the <I>basic execution
wide-character set</I> shall each contain all the members of the basic
source character set, plus control characters representing alert,
backspace, and carriage return, plus a <I>null character</I>
(respectively, <I>null wide character</I>), whose <DEL>representation has
all zero bits</DEL> <INS>value is 0</INS>. For each basic execution
character set...

</BLOCKQUOTE>

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