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    CWG Issue 2719</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="2719"></A><H4>2719.
  
Creating objects in misaligned storage
</H4>
<B>Section: </B>6.8.3&#160; [<A href="https://wg21.link/basic.align">basic.align</A>]
 &#160;&#160;&#160;

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

 <B>Submitter: </B>Jiang An
 &#160;&#160;&#160;

 <B>Date: </B>2023-04-05<BR>


<P>[Accepted as a DR at the June, 2023 meeting.]</P>



<P>A non-allocating form of <TT>operator new</TT> can be used to
create an object in storage that is not suitably aligned for the type
of the object.  Such attempts ought to be undefined behavior.</P>

<P><B>Proposed resolution (approved by CWG 2023-04-28):</B></P>

<OL>
<LI>
<P>Change in 6.8.3 [<A href="https://wg21.link/basic.align#1">basic.align</A>] paragraph 1 as follows:</P>

<BLOCKQUOTE>

Object types have alignment requirements (6.9.2 [<A href="https://wg21.link/basic.fundamental">basic.fundamental</A>],
6.9.4 [<A href="https://wg21.link/basic.compound">basic.compound</A>]) which place restrictions on the addresses
at which an object of that type may be allocated. An alignment is an
implementation-defined integer value representing the number of bytes
between successive addresses at which a given object can be
allocated. An object type imposes an alignment requirement on every
object of that type; stricter alignment can be requested using the
alignment specifier (9.13.2 [<A href="https://wg21.link/dcl.align">dcl.align</A>]). <INS>Attempting to
create an object (6.8.2 [<A href="https://wg21.link/intro.object">intro.object</A>]) in storage that does not
meet the alignment requirements of the object's type is undefined
behavior.</INS>

</BLOCKQUOTE>
</LI>

<LI>
<P>Change in 7.6.2.8 [<A href="https://wg21.link/expr.new#22">expr.new</A>] paragraph 22 as follows:</P>

<BLOCKQUOTE>

[<I>Note 11:</I> When the allocation function returns a value other
than null, it must be a pointer to a block of storage in which space
for the object has been reserved. The block of storage is assumed to
be appropriately aligned <INS>(6.8.3 [<A href="https://wg21.link/basic.align">basic.align</A>])</INS> and
of the requested size. The address of the created object will not
necessarily be the same as that of the block if the object is an
array. &#8212;<I>end note</I>]

</BLOCKQUOTE>
</LI>
</OL>

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