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    CWG Issue 2870</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="2870"></A><H4>2870.
  
Combining absent <I>encoding-prefix</I>es
</H4>
<B>Section: </B>5.13.5&#160; [<A href="https://wg21.link/lex.string">lex.string</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD7
 &#160;&#160;&#160;

 <B>Submitter: </B>Jan Schultke
 &#160;&#160;&#160;

 <B>Date: </B>2024-03-09<BR>


<P>[Accepted as a DR at the June, 2024 meeting.]</P>

<P>(From submission
<A HREF="https://github.com/cplusplus/CWG/issues/511">#511</A>.)</P>

<P>Subclause 5.13.5 [<A href="https://wg21.link/lex.string#7">lex.string</A>] paragraph 7 does not properly
handle the case where both <I>encoding-prefix</I>es are absent:</P>

<BLOCKQUOTE>

The common <I>encoding-prefix</I> for a sequence of
adjacent <I>string-literal</I>s is determined pairwise as follows: If
two <I>string-literal</I>s have the same <I>encoding-prefix</I> , the
common <I>encoding-prefix</I> is that <I>encoding-prefix</I> . If
one <I>string-literal</I> has no <I>encoding-prefix</I> , the
common <I>encoding-prefix</I> is that of the
other <I>string-literal</I>. Any other combinations are ill-formed.

</BLOCKQUOTE>

<P><U>Possible resolution [SUPERSEDED]:</U></P>

<P>Change in 5.13.5 [<A href="https://wg21.link/lex.string#7">lex.string</A>] paragraph 7 as follows:</P>

<BLOCKQUOTE>

The common <I>encoding-prefix</I> for a sequence of
adjacent <I>string-literal</I>s is determined pairwise as
follows: <DEL>If two <I>string-literal</I>s have the same
<I>encoding-prefix</I>, the common <I>encoding-prefix</I> is that
<I>encoding-prefix</I>.</DEL> If one <I>string-literal</I> has no
<I>encoding-prefix</I>, the common <I>encoding-prefix</I> is that of
the other <I>string-literal</I> <INS>or is absent if the other
<I>string-literal</I> has no <I>encoding-prefix</I>. Otherwise,
both <I>string-literal</I>s shall have the same
<I>encoding-prefix</I>, and the common <I>encoding-prefix</I> is that
<I>encoding-prefix</I></INS>. <DEL>Any other combinations are
ill-formed.</DEL>

</BLOCKQUOTE>

<P><B>CWG 2024-05-03</B></P>

<P>CWG preferred a holistic instead of a pairwise approach.</P>

<P><B>Proposed resolution (approved by CWG 2024-05-17):</B></P>

<P>Change in 5.13.5 [<A href="https://wg21.link/lex.string#7">lex.string</A>] paragraph 7 as follows:</P>

<BLOCKQUOTE>

<P class="del">The common <I>encoding-prefix</I> for a sequence of
adjacent <I>string-literal</I>s is determined pairwise as follows: If
two <I>string-literal</I>s have the same <I>encoding-prefix</I> , the
common <I>encoding-prefix</I> is that <I>encoding-prefix</I> . If
one <I>string-literal</I> has no <I>encoding-prefix</I> , the
common <I>encoding-prefix</I> is that of the
other <I>string-literal</I>. Any other combinations are ill-formed.</P>

<P class="ins">
The <I>string-literal</I>s in any sequence of
adjacent <I>string-literal</I>s shall have at most one
unique <I>encoding-prefix</I> among them.  The common
<I>encoding-prefix</I> of the sequence is that <I>encoding-prefix</I>,
if any.</P>

</BLOCKQUOTE>
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