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    CWG Issue 439</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="439"></A><H4>439.
  
Guarantees on casting pointer back to cv-qualified version of original type
</H4>
<B>Section: </B>7.6.1.9&#160; [<A href="https://wg21.link/expr.static.cast">expr.static.cast</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD1
 &#160;&#160;&#160;

 <B>Submitter: </B>Mark Mitchell
 &#160;&#160;&#160;

 <B>Date: </B>30 Oct 2003<BR>


<P>[Voted into WP at April 2005 meeting.]</P>

<P>Paragraph 7.6.1.9 [<A href="https://wg21.link/expr.static.cast#10">expr.static.cast</A>] paragraph 10 says that:</P>

<BLOCKQUOTE>
A value of type pointer to object converted to
"pointer to <I>cv</I> <TT>void</TT>" and back to the
original pointer type will have its original value.
</BLOCKQUOTE>

<P>That guarantee should be stronger.  In particular, given:
<PRE>
  T* p1 = new T;
  const T* p2 = static_cast&lt;const T*&gt;(static_cast&lt;void *&gt;(p1));
  if (p1 != p2)
    abort ();
</PRE>
there should be no call to "abort".  The last sentence of Paragraph
7.6.1.9 [<A href="https://wg21.link/expr.static.cast#10">expr.static.cast</A>] paragraph 10 should be changed to read:</P>

<BLOCKQUOTE>
 A value of type pointer to object converted to "pointer to
<I>cv</I> <TT>void</TT>" and back to the original pointer type
(or a variant of the original pointer type that differs only in the
<I>cv</I>-qualifiers applied to the object type) will have its
original value.
[<I>Example:</I>
<BLOCKQUOTE>
<PRE>
T* p1 = new T;
const T* p2 = static_cast&lt;const T*&gt;(static_cast&lt;void *&gt;(p1));
bool b = p1 == p2; // b <I>will have the value true.</I>
</PRE>
</BLOCKQUOTE>
<I>---end example.</I>]
</BLOCKQUOTE>

<P><B>Proposed resolution:</B></P>

<P>Change 7.6.1.9 [<A href="https://wg21.link/expr.static.cast#10">expr.static.cast</A>] paragraph 10 as indicated:</P>
<BLOCKQUOTE>
A value of type pointer to object converted to "pointer to
<I>cv</I> <TT>void</TT>" and back to the original pointer
type<INS>, possibly with different cv-qualification,</INS> will have
its original value.  <INS>[<I>Example:</I></INS>
<PRE>
<INS>
  T* p1 = new T;
  const T* p2 = static_cast&lt;const T*&gt;(static_cast&lt;void *&gt;(p1));
  bool b = p1 == p2; // b<I> will have the value </I>true.
</INS>
</PRE>
<INS>---<I>end example</I>]</INS>
</BLOCKQUOTE>

<P>
<B>Rationale:</B> The wording "possibly with different
cv-qualification" was chosen over the suggested wording to
allow for changes in cv-qualification at different levels in a
multi-level pointer, rather than only at the object type level.
</P>

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