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    CWG Issue 745</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="745"></A><H4>745.
  
Effect of ill-formedness resulting from <TT>#error</TT>
</H4>
<B>Section: </B>15.9&#160; [<A href="https://wg21.link/cpp.error">cpp.error</A>]
 &#160;&#160;&#160;

 <B>Status: </B>C++23
 &#160;&#160;&#160;

 <B>Submitter: </B>Clark Nelson
 &#160;&#160;&#160;

 <B>Date: </B>13 November, 2008<BR>


<P>[ Resolved by <A HREF="2518.html">issue 2518</A>, adopted in February, 2023. ]</P>

<P>C99 is very clear that a <TT>#error</TT> directive causes a translation
to fail: Clause 4 paragraph 4 says,</P>

<BLOCKQUOTE>

The implementation shall not successfully translate a preprocessing
translation unit containing a <TT>#error</TT> preprocessing directive
unless it is part of a group skipped by conditional inclusion.

</BLOCKQUOTE>

<P>C++, on the other hand, simply says that a <TT>#error</TT> directive
&#8220;renders the program ill-formed&#8221; (15.9 [<A href="https://wg21.link/cpp.error">cpp.error</A>]),
and the only requirement for an ill-formed program is that a diagnostic
be issued; the translation may continue and succeed.  (Noted in passing:
if this difference between C99 and C++ is addressed, it would be helpful
for synchronization purposes in other contexts as well to introduce the
term &#8220;preprocessing translation unit.&#8221;)</P>

<P>See also <A HREF="2518.html">issue 2518</A>.</P>

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