linux手机管理多版本gcc和g++

1. cmake升级参考：

linux手机更新cmake版本

1. gcc和g++升级参考：

linux手机更新 gcc g++ 版本

root@ubuntu-phablet:/# gcc --version

gcc (Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.12) 5.4.0 20160609

Copyright (C) 2015 Free Software Foundation, Inc.

This is free software; see the source for copying conditions.  There is NO

warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

root@ubuntu-phablet:/# gcc-9 --version

gcc-9 (Ubuntu 9.4.0-1ubuntu1~16.04) 9.4.0

Copyright (C) 2019 Free Software Foundation, Inc.

This is free software; see the source for copying conditions.  There is NO

warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

对于c++20已经支持了（g++-9）

root@ubuntu-phablet:/# g++ -std=c++2a

g++: error: unrecognized command line option ‘-std=c++2a’

g++: fatal error: no input files

compilation terminated.

root@ubuntu-phablet:/# g++-9 -std=c++2a

g++-9: fatal error: no input files

compilation terminated.

查看所有g++或gcc版本：

root@ubuntu-phablet:/# ls /usr/bin/g++*

/usr/bin/g++  /usr/bin/g++-5  /usr/bin/g++-9

将默认g++和gcc进行调整：

root@ubuntu-phablet:/# update-alternatives --display gcc

update-alternatives: error: no alternatives for gcc

root@ubuntu-phablet:/# update-alternatives --display g++

update-alternatives: error: no alternatives for g++

root@ubuntu-phablet:/# update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-5 10

update-alternatives: using /usr/bin/gcc-5 to provide /usr/bin/gcc (gcc) in auto mode

root@ubuntu-phablet:/# update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-9 40

update-alternatives: using /usr/bin/gcc-9 to provide /usr/bin/gcc (gcc) in auto mode

root@ubuntu-phablet:/# update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-5 10

update-alternatives: using /usr/bin/g++-5 to provide /usr/bin/g++ (g++) in auto mode

root@ubuntu-phablet:/# update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-9 40

update-alternatives: using /usr/bin/g++-9 to provide /usr/bin/g++ (g++) in auto mode

root@ubuntu-phablet:/# update-alternatives --display gcc

gcc - auto mode

  link best version is /usr/bin/gcc-9

  link currently points to /usr/bin/gcc-9

  link gcc is /usr/bin/gcc

/usr/bin/gcc-5 - priority 10

/usr/bin/gcc-9 - priority 40

root@ubuntu-phablet:/# update-alternatives --display g++

g++ - auto mode

  link best version is /usr/bin/g++-9

  link currently points to /usr/bin/g++-9

  link g++ is /usr/bin/g++

/usr/bin/g++-5 - priority 10

/usr/bin/g++-9 - priority 40

再次测试：