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).