On Thu, Sep 5, 2019 at 3:45 PM Segher Boessenkool <seg...@kernel.crashing.org> wrote: > > [ That's not what a feature test macro is; a feature test macro allows the > user to select some optional behaviour. Things like _GNU_SOURCE. ]
Yes and no. GNU libc defines feature test macros like you say, but C++'s feature macros are like Rasmus/Nick are saying. I think libc's definition is weird, I would call those "feature selection macros" instead, because the user is selecting between some features (whether to enable or not, for instance), rather than testing for the features. > Why would GCC want to have macros for all features it has? That would be > quite a few new ones every release. Maybe GCC wouldn't, but its users, they surely would. For anything that 1) is a new language feature, 2) breaks backwards-compatibility with previous (or other compilers) and 3) is expected to be used by end users, yes, it would be very useful to have. For the same reasons C++ is adding feature test macros all over the place nowadays and it is considered good practice (see SD-6: SG10 Feature Test Recommendations). Cheers, Miguel
