[Bug c++/105499] New: inconsistency between -Werror=c++-compat and g++ in __extension__ block
vincent-gcc at vinc17 dot net
gcc-bugzilla@gcc.gnu.org
Fri May 6 00:12:51 GMT 2022
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105499
Bug ID: 105499
Summary: inconsistency between -Werror=c++-compat and g++ in
__extension__ block
Product: gcc
Version: 11.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: vincent-gcc at vinc17 dot net
Target Milestone: ---
Consider
int *f (void *q)
{
return __extension__ ({ int *p = q; p; });
}
With GCC 11.3.0 under Debian (Debian package), I get the following:
$ gcc -Werror=c++-compat -c tst.c
$ g++ -c tst.c
tst.c: In function ‘int* f(void*)’:
tst.c:3:36: error: invalid conversion from ‘void*’ to ‘int*’ [-fpermissive]
3 | return __extension__ ({ int *p = q; p; });
| ^
| |
| void*
so no errors with "gcc -Werror=c++-compat", but an error with g++. This is not
consistent. Either this is regarded as a valid extension in C++ so that both
should succeed, or this is not valid C++ code even in __extension__ so that
both should fail.
Same issue with various GCC versions from 4.9 to 11.3.0.
AFAIK, the purpose of -Wc++-compat is to test whether code would still pass
when replacing C compilation by C++ (there might be false positives or false
negatives, but this should not be the case with the above example).
FYI, I got the above issue while testing GNU MPFR (tested with
-Werror=c++-compat first, and with g++ a bit later in a more extensive test).
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