This code: > #include <math.h> > > int main() { return !isfinite(1.0); } triggers this warning: > $ cc -Wall -Wextra -pedantic -std=gnu99 -c x.c > x.c:4:22: warning: '_Generic' is a C11 extension [-Wc11-extensions] > int main() { return !isfinite(1.0); } > ^ > /usr/include/math.h:111:21: note: expanded from macro 'isfinite' > #define isfinite(x) __fp_type_select(x, __isfinitef, __isfinite, __isfinitel) > ^ > /usr/include/math.h:82:39: note: expanded from macro '__fp_type_select' > #define __fp_type_select(x, f, d, ld) _Generic((x), \ > ^ > 1 warning generated. The igraph project used -Werror and this problem caused build failure.
Other packages are also affected: https://www.google.com/search?q=%22%27_Generic%27+is+a+C11+extension%22+freebsd
Why is this code trying to compile with -pedantic? If you use that, you know that you will receive pedantic warnings, which are not usually useful. I'd say the solution is "do not use -pedantic"? Then it works just fine.
(In reply to Dimitry Andric from comment #2) Is appears that many projects turn on -pedantic and get this warning which is converted to error with -Werror. Example is igraph project: https://github.com/igraph/igraph/issues/1748
A commit in branch main references this bug: URL: https://cgit.FreeBSD.org/src/commit/?id=7702d940ec9a27fd4ab9e3991fc582b369b5eedc commit 7702d940ec9a27fd4ab9e3991fc582b369b5eedc Author: Dimitry Andric <dim@FreeBSD.org> AuthorDate: 2021-04-08 11:13:15 +0000 Commit: Dimitry Andric <dim@FreeBSD.org> CommitDate: 2021-04-08 16:20:32 +0000 Avoid -pedantic warnings about using _Generic in __fp_type_select When compiling parts of math.h with clang using a C standard before C11, and using -pedantic, it will result in warnings similar to: bug254714.c:5:11: warning: '_Generic' is a C11 extension [-Wc11-extensions] return !isfinite(1.0); ^ /usr/include/math.h:111:21: note: expanded from macro 'isfinite' ^ /usr/include/math.h:82:39: note: expanded from macro '__fp_type_select' ^ This is because the block that enables use of _Generic is conditional not only on C11, but also on whether the compiler advertises support for C generic selections via __has_extension(c_generic_selections). To work around the warning without having to pessimize the code, use the __extension__ keyword, which is supported by both clang and gcc. While here, remove the check for __clang__, as _Generic has been supported for a long time by gcc too now. Reported by: yuri PR: 254714 MFC after: 1 week lib/msun/src/math.h | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)
A commit in branch stable/13 references this bug: URL: https://cgit.FreeBSD.org/src/commit/?id=7abb639572d847d4c5ff134f4441cb39447b3c9c commit 7abb639572d847d4c5ff134f4441cb39447b3c9c Author: Dimitry Andric <dim@FreeBSD.org> AuthorDate: 2021-04-08 11:13:15 +0000 Commit: Dimitry Andric <dim@FreeBSD.org> CommitDate: 2021-04-15 16:51:08 +0000 Avoid -pedantic warnings about using _Generic in __fp_type_select When compiling parts of math.h with clang using a C standard before C11, and using -pedantic, it will result in warnings similar to: bug254714.c:5:11: warning: '_Generic' is a C11 extension [-Wc11-extensions] return !isfinite(1.0); ^ /usr/include/math.h:111:21: note: expanded from macro 'isfinite' ^ /usr/include/math.h:82:39: note: expanded from macro '__fp_type_select' ^ This is because the block that enables use of _Generic is conditional not only on C11, but also on whether the compiler advertises support for C generic selections via __has_extension(c_generic_selections). To work around the warning without having to pessimize the code, use the __extension__ keyword, which is supported by both clang and gcc. While here, remove the check for __clang__, as _Generic has been supported for a long time by gcc too now. Reported by: yuri PR: 254714 lib/msun/src/math.h | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)
A commit in branch stable/12 references this bug: URL: https://cgit.FreeBSD.org/src/commit/?id=81c5f1451c4e2221413a9b05aadcfd74a1182848 commit 81c5f1451c4e2221413a9b05aadcfd74a1182848 Author: Dimitry Andric <dim@FreeBSD.org> AuthorDate: 2021-04-08 11:13:15 +0000 Commit: Dimitry Andric <dim@FreeBSD.org> CommitDate: 2021-04-15 16:50:56 +0000 Avoid -pedantic warnings about using _Generic in __fp_type_select When compiling parts of math.h with clang using a C standard before C11, and using -pedantic, it will result in warnings similar to: bug254714.c:5:11: warning: '_Generic' is a C11 extension [-Wc11-extensions] return !isfinite(1.0); ^ /usr/include/math.h:111:21: note: expanded from macro 'isfinite' ^ /usr/include/math.h:82:39: note: expanded from macro '__fp_type_select' ^ This is because the block that enables use of _Generic is conditional not only on C11, but also on whether the compiler advertises support for C generic selections via __has_extension(c_generic_selections). To work around the warning without having to pessimize the code, use the __extension__ keyword, which is supported by both clang and gcc. While here, remove the check for __clang__, as _Generic has been supported for a long time by gcc too now. Reported by: yuri PR: 254714 lib/msun/src/math.h | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)
A commit in branch stable/11 references this bug: URL: https://cgit.FreeBSD.org/src/commit/?id=b582d1422b4db6c22ff061a32257a83405d06cc9 commit b582d1422b4db6c22ff061a32257a83405d06cc9 Author: Dimitry Andric <dim@FreeBSD.org> AuthorDate: 2021-04-08 11:13:15 +0000 Commit: Dimitry Andric <dim@FreeBSD.org> CommitDate: 2021-04-15 10:24:28 +0000 Avoid -pedantic warnings about using _Generic in __fp_type_select When compiling parts of math.h with clang using a C standard before C11, and using -pedantic, it will result in warnings similar to: bug254714.c:5:11: warning: '_Generic' is a C11 extension [-Wc11-extensions] return !isfinite(1.0); ^ /usr/include/math.h:111:21: note: expanded from macro 'isfinite' ^ /usr/include/math.h:82:39: note: expanded from macro '__fp_type_select' ^ This is because the block that enables use of _Generic is conditional not only on C11, but also on whether the compiler advertises support for C generic selections via __has_extension(c_generic_selections). To work around the warning without having to pessimize the code, use the __extension__ keyword, which is supported by both clang and gcc. While here, remove the check for __clang__, as _Generic has been supported for a long time by gcc too now. Reported by: yuri PR: 254714 lib/msun/src/math.h | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)
A commit in branch stable/10 references this bug: URL: https://cgit.FreeBSD.org/src/commit/?id=74b123c0a5ecfe2081c47de98820cdfabb64024d commit 74b123c0a5ecfe2081c47de98820cdfabb64024d Author: Dimitry Andric <dim@FreeBSD.org> AuthorDate: 2021-04-08 11:13:15 +0000 Commit: Dimitry Andric <dim@FreeBSD.org> CommitDate: 2021-04-15 10:26:48 +0000 Avoid -pedantic warnings about using _Generic in __fp_type_select When compiling parts of math.h with clang using a C standard before C11, and using -pedantic, it will result in warnings similar to: bug254714.c:5:11: warning: '_Generic' is a C11 extension [-Wc11-extensions] return !isfinite(1.0); ^ /usr/include/math.h:111:21: note: expanded from macro 'isfinite' ^ /usr/include/math.h:82:39: note: expanded from macro '__fp_type_select' ^ This is because the block that enables use of _Generic is conditional not only on C11, but also on whether the compiler advertises support for C generic selections via __has_extension(c_generic_selections). To work around the warning without having to pessimize the code, use the __extension__ keyword, which is supported by both clang and gcc. While here, remove the check for __clang__, as _Generic has been supported for a long time by gcc too now. Reported by: yuri PR: 254714 lib/msun/src/math.h | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)