~> sudo update-alternatives --config gcc
[sudo] root 的密码:
There are 2 choices for the alternative gcc (providing /usr/bin/gcc).
Selection Path Priority Status
------------------------------------------------------------
0 /usr/bin/gcc-9 90 auto mode
* 1 /usr/bin/gcc-7 70 manual mode
2 /usr/bin/gcc-9 90 manual mode
Press <enter> to keep the current choice [*], or type selection number: 1
~> sudo update-alternatives --config g++
There are 2 choices for the alternative g++ (providing /usr/bin/g++).
Selection Path Priority Status
------------------------------------------------------------
0 /usr/bin/g++-9 90 auto mode
* 1 /usr/bin/g++-7 70 manual mode
2 /usr/bin/g++-9 90 manual mode
Press <enter> to keep the current choice [*], or type selection number: 1