How to build 6.14.08 w/ c++17 and gcc8.2

ROOT
1

What are the magic words to build root 6.14.08 w/ c++17 and gcc8.2 (or gcc8.3)? I have tried all combinations of
cmake -Dcxx=17
cmake -Dcxx17=ON
cmake -DCMAKE_CXX_STANDARD=17

and I still see the compilation commands littered with std=c++11 and std=c++1z, and then various failures due to standards mis-matches.

even when I use all three I see this from the cmake output:
– Compiler Flags: -Wno-implicit-fallthrough -Wno-noexcept-type -pipe -m64 -Wshadow -Wall -W -Woverloaded-virtual -fsigned-char -pthread -std=c++1z

thanks, Charles.

ROOT Version: 6.14.08
Platform: x86 (cori.lbl.gov)
Compiler: gcc 8.2

2

Could you try to compile the lastest ROOT version (6.18.02) with cmake -Dcxx17=ON to see whether it works?

3

Hi,
note that c++1z is an alternative name for c++17, so that cmake output looks ok.

If you get standard mismatches, try erasing the build directory and start clean.

In case it helps: if I remember correctly, for v6.14 -Dcxx17=ON should be the only flag required. In later versions we switched to the standard -DCMAKE_CXX_STANDARD=17. You can check the output you get when you give the cmake configuration command (cmake -Dcxx17=ON -D... path/to/root): it’s verbose, but it should tell you what standard is being set for the project.

Hope this helps!
Enrico

4

… And please post the actual errors and compiler invocations with wrong compilation flags you see. Thanks!

5

It appears that-Dcxx17=ON did the trick (meaning I was able to use it with c++17 compliant code that was cmake’d with -DCMAKE_CXX_STANDARD=17). -Dcxx=17 and -DCMAKE_CXX_STANDARD=17 don’t work with 6.14.08.

I was a little confused by root-config --clfags which gave"-std=c++17" instead of the "-std=c++1z" I was expecting.

Thanks for the assistance!

6

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