I learned from the discuss a few days ago:
We use C11 and C++11 standard and our current toolchain for arm target (STM boards) is
gcc version 6.3.1 20170620 (release) [ARM/embedded-6-branch revision 249437] (GNU Tools for ARM Embedded Processors 6-2017-q2-update).
For SITL, we don’t care about the toolchain. We support up to GCC9 and normally also work with gcc-musl and clang.
I want to know how to modify the code. I can use the C++14 standard to compile ardupilot.