Rootcling warnings when compiling ROOT 6.36.08 with C++23

ROOT
1

Hi,

when compiling ROOT 6.36.08 on Debian12 with C++ standard 23 I get warnings from rootcling which I would not expect. The warning is attached below. The installation works and I couldn’t see any problem on first glance. I can also build my project unfortunately getting the same warnings.

The configuration correctly encounters for the C++ standard and passes it correctly to the compiler. For me it looks like rootcling does not know that a different C++ standard is used and somehow uses the __cplusplus default value instead the one defined when using -std=c++23.

[ 52%] Generating G__Thread.cxx, ../../lib/libThread.rootmap

In file included from input_line_3:2:

In file included from /tmp/uhlig/fairsoft/build_debian13/Build/root/include/Rtypes.h:23:

In file included from /tmp/uhlig/fairsoft/build_debian13/Build/root/include/RtypesCore.h:23:

In file included from /tmp/uhlig/fairsoft/build_debian13/Build/root/include/ROOT/RConfig.hxx:23:

/tmp/uhlig/fairsoft/build_debian13/Build/root/include/RConfigure.h:30:4: warning: "The C++ standard in this build does not match ROOT configuration (202100L); this might cause unexpected issues" [-W#warnings]

#  warning "The C++ standard in this build does not match ROOT configuration (202100L); this might cause unexpected issues"

   ^

ROOT Version: 6.36.08
Platform: linuxx8664gcc
Compiler: GCC 12.2

System: Linux-4.18.0-513.24.1.el8_9.x86_64

ROOT Platform: linux

ROOT Architecture: linuxx8664gcc

Processor: 128 core AMD EPYC 7713 64-Core Processor (x86_64)

Build type: RelWithDebInfo

Install path: /tmp/uhlig/fairsoft/install

Compiler: GNU 12.2.0

C++ standard: 23

Ciao

Florian

2

Dear @uhlig ,

Thanks for reaching out to the forum!

I’ve seen such errors in the past where on the same environment/machine there were some leftover ROOT builds or installations. Or sometimes when a pre-existing ROOT build is rebuilt incrementally. Can you make sure that you are rebuilding ROOT from scratch, in a clean environment, and no other ROOT installations are present on the machine (or they are properly isolated)?

Cheers,
Vincenzo