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    CWG Issue 1504</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="1504"></A><H4>1504.
  
Pointer arithmetic after derived-base conversion
</H4>
<B>Section: </B>7.6.6&#160; [<A href="https://wg21.link/expr.add">expr.add</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD3
 &#160;&#160;&#160;

 <B>Submitter: </B>Lo&#239;c Joly
 &#160;&#160;&#160;

 <B>Date: </B>2012-05-20<BR>


<P>[Moved to DR at the April, 2013 meeting.]</P>



<P>The current wording is not sufficiently clear that a pointer to a
base class subobject of an array element cannot be used in pointer
arithmetic.</P>

<P><B>Proposed resolution (October, 2012):</B></P>

<P>Add the following as a new paragraph before 7.6.6 [<A href="https://wg21.link/expr.add#7">expr.add</A>] paragraph 7:
</P>

<BLOCKQUOTE>

<P><INS>For addition or subtraction, if the expressions <TT>P</TT> or
<TT>Q</TT> have type &#8220;pointer to <I>cv</I> <TT>T</TT>", where
<TT>T</TT> is different from the cv-unqualified array element type,
the behavior is undefined. [<I>Note:</I> In particular, a pointer to a
base class cannot be used for pointer arithmetic when the array
contains objects of a derived class type. &#8212;<I>end
note</I>]</INS></P>

<P>If the value <TT>0</TT> is added to or subtracted...</P>

</BLOCKQUOTE>

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