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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Trigraph support in various C language modes"
href="https://bugs.llvm.org/show_bug.cgi?id=47645">47645</a>
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<th>Summary</th>
<td>Trigraph support in various C language modes
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<th>Product</th>
<td>clang
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<th>Version</th>
<td>trunk
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<th>Hardware</th>
<td>PC
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<th>OS</th>
<td>Windows NT
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>enhancement
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>C
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>aaron@aaronballman.com
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<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<pre>Clang's trigraph support is disabled by default when the language standard is
set to GNU C mode. Not supporting trigraphs is perhaps reasonable because the
user is specifying that they want something other than standard C.
However, when *no* -std= option is passed on the command line, we silently
default to gnu17 mode which then disables this standard C feature and that
seems less reasonable to me because this is a case where we're *removing*
support for a feature rather than adding a conforming extension. The user is
saying "here's my C file, please compile it" and I think we should be able to
compile conforming C in that case (for some C standard version, but all of them
currently support trigraphs).
Confounding matters somewhat, we define __STDC__ to 1 in GNU mode despite
trigraph support in C being mandatory.
Should trigraphs remain enabled when no -std is present (even though we would
still default to gnu17) so that users can compile conforming C code?
Should __STDC__ be paying attention to whether trigraph support is enabled or
not?</pre>
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