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    CWG Issue 678</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="678"></A><H4>678.
  
Language linkage of member function parameter types and the ODR
</H4>
<B>Section: </B>6.3&#160; [<A href="https://wg21.link/basic.def.odr">basic.def.odr</A>]
 &#160;&#160;&#160;

 <B>Status: </B>C++11
 &#160;&#160;&#160;

 <B>Submitter: </B>James Widman
 &#160;&#160;&#160;

 <B>Date: </B>15 February, 2008<BR>


<P>[Voted into WP at August, 2010 meeting.]</P>



<P>I thought this case would result in undefined behavior according to
6.3 [<A href="https://wg21.link/basic.def.odr">basic.def.odr</A>]:</P>

<PRE>
    // t.h:
    struct A { void (*p)(); };

    // t1.cpp:
    #include "t.h" // A::p<SPAN CLASS="cmnt"> is a pointer to C++ func</SPAN>

    // t2.cpp:
    extern "C" {
    #include "t.h" // A::p<SPAN CLASS="cmnt"> is a pointer to C func</SPAN>
    }
</PRE>

<P>...but I don't see how any of the bullets in the list in paragraph
5 apply.</P>

<P><B>Proposed resolution (March, 2010):</B></P>

<P>Add a new bullet following 6.3 [<A href="https://wg21.link/basic.def.odr#5">basic.def.odr</A>] paragraph 5,
second bullet:</P>

<BLOCKQUOTE>

<P>...Given such an entity named <TT>D</TT> defined in more than one
translation unit, then</P>

<UL>
<LI><P>each definition of <TT>D</TT> shall consist of the
same sequence of tokens; and</P></LI>

<LI><P>in each definition of <TT>D</TT>, corresponding names,
looked up according to 6.5 [<A href="https://wg21.link/basic.lookup">basic.lookup</A>], shall refer to
an entity defined within the definition of <TT>D</TT>, or shall
refer to the same entity, after overload resolution (12.2 [<A href="https://wg21.link/over.match">over.match</A>]) and after matching of partial template
specialization (13.10.4 [<A href="https://wg21.link/temp.over">temp.over</A>]), except that a name
can refer to a const object with internal or no linkage if the
object has the same literal type in all definitions of
<TT>D</TT>, and the object is initialized with a constant
expression (7.7 [<A href="https://wg21.link/expr.const">expr.const</A>]), and the value (but not
the address) of the object is used, and the object has the same
value in all definitions of <TT>D</TT>; and</P></LI>

<LI><P><INS>in each definition of <TT>D</TT>, corresponding
entities shall have the same language linkage; and</INS></P></LI>

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

</UL>

</BLOCKQUOTE>

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