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    CWG Issue 1175</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="1175"></A><H4>1175.
  
Disambiguating user-defined literals
</H4>
<B>Section: </B>5.13.9&#160; [<A href="https://wg21.link/lex.ext">lex.ext</A>]
 &#160;&#160;&#160;

 <B>Status: </B>C++11
 &#160;&#160;&#160;

 <B>Submitter: </B>Sebastian Gesemann
 &#160;&#160;&#160;

 <B>Date: </B>2010-08-10<BR>


<P>[Voted into the WP at the March, 2011 meeting as part of paper N3262.]</P>

<P>A user-defined literal like <TT>0x123DZ</TT> could be
parsed either as a <I>hexadecimal-literal</I> of <TT>0x123</TT> and a
<I>ud-suffix</I> of <TT>DZ</TT> or as a <I>hexadecimal-literal</I> of
<TT>0x123D</TT> and a <I>ud-suffix</I> of <TT>Z</TT>.  There does not
appear to be a rule that disambiguates the two possible parses.</P>

<P><B>Proposed resolution (November, 2010) [SUPERSEDED]:</B></P>

<P>Change 5.13.9 [<A href="https://wg21.link/lex.ext#1">lex.ext</A>] paragraph 1 as follows:</P>

<BLOCKQUOTE>

If a token matches both <I>user-defined-literal</I> and another
literal kind, it is treated as the latter.  [<I>Example:</I>
<TT>123_km</TT>, <TT>1.2LL</TT>, <TT>"Hello"s</TT> are all
<I>user-defined-literal</I>s, but <TT>12LL</TT> is an
<I>integer-literal</I>.  &#8212;<I>end example</I>] <INS>The syntactic
nonterminal preceding the <I>ud-suffix</I> in a
<I>user-defined-literal</I> is taken to be the longest sequence of
characters that could match that nonterminal. [<I>Example:</I> The
<I>ud-suffix</I> in <TT>1.0e0X</TT> is <TT>X</TT>, not <TT>e0X</TT>;
in <TT>0x1DZ</TT>, the <I>ud-suffix</I> is <TT>Z</TT>, not
<TT>DZ</TT>. &#8212;<I>end example</I>]</INS>

</BLOCKQUOTE>

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