Libstdc++ has been using __STRICT_ANSI__ for years, e.g. to decide whether or not std::is_integral<__int128> should be true.
gcc/ChangeLog: * doc/cpp.texi (Common Predefined Macros): Mention that __STRICT_ANSI__ is used by libstdc++ too. OK for trunk? I'd also like to tell users they're not allowed to undefine the macro, would that be acceptable, or is that supposed to work? I don't see how it's possible to make it work with libstdc++ if users do stupid things like: #include <type_traits> #undef __STRICT_ANSI__ #include <iterator> This causes the library to be in an inconsistent (broken) state, because some templates are defined according to strict ISO C++ rules and then other templates are not, but assume the earlier definitions are consistent. We frequently see users doing -std=c++11 -U__STRICT_ANSI__ which makes me smash my head on the table. Just use -std=gnu++11 and stop being dumb.
commit c516abe37ef82444e125b32933ea44a00a99d1ec Author: Jonathan Wakely <jwak...@redhat.com> Date: Wed Dec 16 13:21:24 2020 doc: Document that libstdc++ uses __STRICT_ANSI__ Libstdc++ has been using __STRICT_ANSI__ for years, e.g. to decide whether or not std::is_integral<__int128> should be true. gcc/ChangeLog: * doc/cpp.texi (Common Predefined Macros): Mention that __STRICT_ANSI__ is used by libstdc++ too. diff --git a/gcc/doc/cpp.texi b/gcc/doc/cpp.texi index 5dcd67259e3..c5cdd5cb069 100644 --- a/gcc/doc/cpp.texi +++ b/gcc/doc/cpp.texi @@ -1996,8 +1996,8 @@ testing @code{@w{(__GNUC__ && __cplusplus)}}. GCC defines this macro if and only if the @option{-ansi} switch, or a @option{-std} switch specifying strict conformance to some version of ISO C or ISO C++, was specified when GCC was invoked. It is defined to @samp{1}. -This macro exists primarily to direct GNU libc's header files to use only -definitions found in standard C. +This macro exists primarily to direct libstdc++ and GNU libc's header files +to use only definitions found in standard C and C++. @item __BASE_FILE__ This macro expands to the name of the main input file, in the form