<HTML>
<HEAD>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<TITLE>
    CWG Issue 1502</TITLE>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<STYLE TYPE="text/css">
  INS { text-decoration:none; font-weight:bold; background-color:#A0FFA0 }
  .INS { text-decoration:none; background-color:#D0FFD0 }
  DEL { text-decoration:line-through; background-color:#FFA0A0 }
  .DEL { text-decoration:line-through; background-color: #FFD0D0 }
  @media (prefers-color-scheme: dark) {
    HTML { background-color:#202020; color:#f0f0f0; }
    A { color:#5bc0ff; }
    A:visited { color:#c6a8ff; }
    A:hover, a:focus { color:#afd7ff; }
    INS { background-color:#033a16; color:#aff5b4; }
    .INS { background-color: #033a16; }
    DEL { background-color:#67060c; color:#ffdcd7; }
    .DEL { background-color:#67060c; }
  }
  SPAN.cmnt { font-family:Times; font-style:italic }
</STYLE>
</HEAD>
<BODY>
<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="1502"></A><H4>1502.
  
Value initialization of unions with member initializers
</H4>
<B>Section: </B>9.5&#160; [<A href="https://wg21.link/dcl.init">dcl.init</A>]
 &#160;&#160;&#160;

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

 <B>Submitter: </B>Richard Smith
 &#160;&#160;&#160;

 <B>Date: </B>2012-05-06<BR>


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



<P>According to 9.5 [<A href="https://wg21.link/dcl.init#7">dcl.init</A>] paragraph 7,</P>

<BLOCKQUOTE>

<P>To <I>value-initialize</I> an object of type <TT>T</TT> means:</P>

<UL>
<LI><P>if <TT>T</TT> is a (possibly cv-qualified) class type (
Clause 11 [<A href="https://wg21.link/class">class</A>]) with either no default constructor
(11.4.5 [<A href="https://wg21.link/class.ctor">class.ctor</A>]) or a default constructor that is
user-provided or deleted, then the object is default-initialized;
</P></LI>

<LI><P>if <TT>T</TT> is a (possibly cv-qualified) non-union class type without a
user-provided or deleted default constructor, then the object is
zero-initialized and, if <TT>T</TT> has a non-trivial default constructor,
default-initialized;
</P></LI>

<LI><P>if <TT>T</TT> is an array type, then each element is value-initialized;
</P></LI>

<LI><P>otherwise, the object is zero-initialized.
</P></LI>

</UL>

</BLOCKQUOTE>

<P>In an example like</P>

<PRE>
  union U { int a = 5; };
  int main() { return U().a; }
</PRE>

<P>this means that the value returned is <TT>0</TT>, because none of the
first three bullets apply.  Should the &#8220;non-union&#8221;
restriction be dropped from the second bullet?</P>

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

<P>Change 9.5 [<A href="https://wg21.link/dcl.init#7">dcl.init</A>] paragraph 7 as follows:</P>

<BLOCKQUOTE>

<P>To <I>value-initialize</I> an object of type <TT>T</TT> means:</P>

<UL>
<LI><P>...</P></LI>

<LI><P>if <TT>T</TT> is a (possibly cv-qualified) <DEL>non-union</DEL>
class type without a user-provided or deleted default constructor,
then the object is zero-initialized and, if <TT>T</TT> has a
non-trivial default constructor, default-initialized;</P></LI>

<LI><P>...</P></LI>

</UL>

</BLOCKQUOTE>

<BR><BR>
</BODY>
</HTML>
