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    CWG Issue 810</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="810"></A><H4>810.
  
Block-scope <TT>thread_local</TT> variables should be implicitly <TT>static</TT>
</H4>
<B>Section: </B>9.2.2&#160; [<A href="https://wg21.link/dcl.stc">dcl.stc</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD2
 &#160;&#160;&#160;

 <B>Submitter: </B>UK
 &#160;&#160;&#160;

 <B>Date: </B>3 March, 2009<BR><BR>


<A href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3086.html#UK87">N2800 comment
  UK&#160;87<BR></A>

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

<P>According to 9.2.2 [<A href="https://wg21.link/dcl.stc#4">dcl.stc</A>] paragraph 4,</P>

<BLOCKQUOTE>

The <TT>thread_local</TT> specifier shall be applied only to the names
of objects or references of namespace scope and to the names of
objects or references of block scope that also specify
<TT>static</TT>.

</BLOCKQUOTE>

<P>
Why require two keywords, where one on its own becomes ill-formed?
<TT>thread_local</TT> should imply <TT>static</TT> in this case, and
the combination of keywords should be banned rather than
required. This would also eliminate the one of two exceptions
documented in paragraph 1.
</P>

<P><B>Notes from the July, 2009 meeting:</B></P>

<P>The consensus of the CWG was that <TT>thread_local</TT> should
imply <TT>static</TT>, as suggested, but that the combination should
still be allowed (it is needed, for example, for thread-local static
data members).</P>

<P><B>Proposed resolution (October, 2009):</B></P>

<P>Change 9.2.2 [<A href="https://wg21.link/dcl.stc#4">dcl.stc</A>] paragraph 4 as follows:</P>

<BLOCKQUOTE>

The <TT>thread_local</TT> specifier <INS>indicates that the named
entity has thread storage duration (6.8.6.3 [<A href="https://wg21.link/basic.stc.thread">basic.stc.thread</A>]).
It</INS> shall be applied only to the names of objects or references
of namespace <DEL>scope, to the names of objects or references
of</DEL> <INS>or</INS> block scope <DEL>that also specify
<TT>extern</TT> or <TT>static</TT>,</DEL> and to the names of static
data members. <DEL>It specifies that the named object or reference has
thread storage duration (6.8.6.3 [<A href="https://wg21.link/basic.stc.thread">basic.stc.thread</A>]).</DEL> <INS>When
<TT>thread_local</TT> is applied to a variable of block scope the
<I>storage-class-specifier</I> <TT>static</TT> is implied if it does
not appear explicitly.</INS>

</BLOCKQUOTE>

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