Experimental Physics and
Industrial Control System

Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov> · Fri, 7 Jul 2023 12:36:14 -0700

Do you mean "changing language standard version"?

On 7/7/23 12:12, Pierrick M Hanlet via Tech-talk wrote:

Greetings all,
I'd like to build our EPICS software (starting on an Alma Linux 9 platform) for
C++17 or even C++20.

What is motivating this?  imo. language version might best be
decided on a per-module basis.  eg. for PVXS I set -std=c++11

I haven't tried, but I would not be surprised if some of our
more... mature c++ code might not compile with c++20.

On the chance that you are thinking the -std= effects ABI,
you will want to read:

https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_dual_abi.html

  I'm presently building with C++11 by adding
-std=c++11 to the USR_CXXFLAGS in  configure/CONFIG_COMMON.

USR_* is probably not the best place to put this if you want to
effect downstream builds as well.  Some module builds will
overwrite these variables instead of appending.

Looking at some places where this is already done in base might
provide a starting point.

$ git grep '\-std='

...

configure/os/CONFIG.Common.RTEMS-uC5282:ARCH_DEP_CXXFLAGS_5 = -std=c++98
configure/os/CONFIG.Common.solaris-sparc-gnu:POSIX_CFLAGS = -std=gnu99 -D_POSIX_C_SOURCE=200112L
configure/os/CONFIG.Common.solaris-x86-gnu:POSIX_CFLAGS = -std=gnu99 -D_POSIX_C_SOURCE=200112L

  However,
when I tried c++20/c++17/c++14 and it failed in every case with:

  * g++: error: unrecognized command line option ‘-std=c++20’

Could you share the exact command invocation which gives this error?

(also, which GCC version?)

somewhere in the middle of building libcom - after the compilation call to
resourceLib.

A colleague of mine played with the configure/CONFIG.gnuCommon and
had a different level of success and failure.

Any help, even pointing me to the correct documentation would be
greatly appreciated.
Cheers,
Pierrick

--
Pierrick Hanlet
Fermi National Accelerator
Accelerator Front End Controls
+1-630-840-5555 -- lab
+1-312-687-4980 -- mobile

"Whether you think you can or think you can't, you're right" -- Henry Ford

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System