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    CWG Issue 1449</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="1449"></A><H4>1449.
  
Narrowing conversion of negative value to unsigned type
</H4>
<B>Section: </B>9.5.5&#160; [<A href="https://wg21.link/dcl.init.list">dcl.init.list</A>]
 &#160;&#160;&#160;

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

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

 <B>Date: </B>2012-01-28<BR>


<P>[Moved to DR at the October, 2012 meeting.]</P>



<P>According to 9.5.5 [<A href="https://wg21.link/dcl.init.list#7">dcl.init.list</A>] paragraph 7, an implicit
conversion</P>

<BLOCKQUOTE>

from an integer type or unscoped enumeration type to an integer type
that cannot represent all the values of the original type, except
where the source is a constant expression and the actual value after
conversion will fit into the target type and will produce the original
value when converted back to the original type.

</BLOCKQUOTE>

<P>As is made plain in the examples in that paragraph, a conversion of
a negative value to an unsigned type is intended to be a narrowing
conversion; however, the phrase &#8220;actual value after
conversion&#8221; makes this intent unclear, especially since the
round-trip conversion between signed and unsigned types might well
yield the original value.</P>

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

<P>Change 9.5.5 [<A href="https://wg21.link/dcl.init.list#7">dcl.init.list</A>] paragraph 7 as follows:</P>

<BLOCKQUOTE>

<P>A <I>narrowing conversion</I> is an implicit conversion</P>

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

<LI><P>from an integer type or unscoped enumeration type to an integer
type that cannot represent all the values of the original type, except
where the source is a constant expression <DEL>and the actual value
after conversion</DEL> <INS>whose value after integral
promotions</INS> will fit into the target type <DEL>and will produce the
original value when converted back to the original type</DEL>.</P></LI>

</UL>

<P>[<I>Note:</I>...</P>

</BLOCKQUOTE>

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