Does use of C++17 std::filesystem REQUIRE MacOS 10.15? (Xcode 11.1)
It means that (using Apple's tools/libraries), you cannot use std::filesystem in a project targeting a version of Mac OS before 10.15.
If you have a new enough Xcode, etc. you should be able to build a project on 10.14 (say) that targets 10.15 and uses filesystem types and calls. But it won't run on 10.14.
macOS Clang C++17 filesystem header not found
Libc++, which is the C++ standard library on OS X, has not moved <experimental/filesystem> to <filesystem> yet because the specification is not stable.
Hopefully <filesystem> will be a part of the Clang 6.0 release. (We missed 5.0)
Broken c++ std libraries on macOS High Sierra 10.13
I had exactly the same problem after transferring to macOS High Sierra (though, errors were not the same, but similar).
I found a workaround by renaming /usr/local/include to /usr/local/include_old (well, name does not really matter, just the fact that g++/clang will not search for headers in this folder anymore).
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