Standalone compillation on Ubuntu 20.04 failing
With ROOT 6.18 compilation on Ubuntu 20.04 (gcc9.3) is horribly broken, the issue may well be within ROOT. With ROOT 6.22.0 things look less dire and it should be possible to fix the issues showing up. These are mainly comprised of some missing includes which thus far may have slipped due to some compiler details. At least these includes should be fixed to improve compatibility.
Edit: after some first investigations it appear like an issue related to the C++ standard level used. Disabling a potential compilation using c++17 flags works (Ubutnu 20.04, gcc9.3). However, enabling c++17 flags (-std=c++17
) results in plenty of errors tracing back into ROOT headers. Interestingly most of these errors are related to std::string_view
which (as the errors also state) requires c++17 or newer (and should be well supported by gcc9.3)