Ubuntu下切换GCC版本, main slave problem

ls /usr/bin/gcc* -l
lrwxrwxrwx 1 root root 21 6月   2 09:38 /usr/bin/gcc -> /etc/alternatives/gcc
lrwxrwxrwx 1 root root 23 5月  29 15:49 /usr/bin/gcc-10 -> x86_64-linux-gnu-gcc-10
lrwxrwxrwx 1 root root 22 4月   2  2020 /usr/bin/gcc-8 -> x86_64-linux-gnu-gcc-8
lrwxrwxrwx 1 root root 22 8月   8  2020 /usr/bin/gcc-9 -> x86_64-linux-gnu-gcc-9
lrwxrwxrwx 1 root root  8 3月  20  2020 /usr/bin/gcc-ar -> gcc-ar-9
lrwxrwxrwx 1 root root 26 5月  29 15:49 /usr/bin/gcc-ar-10 -> x86_64-linux-gnu-gcc-ar-10
lrwxrwxrwx 1 root root 25 4月   2  2020 /usr/bin/gcc-ar-8 -> x86_64-linux-gnu-gcc-ar-8
lrwxrwxrwx 1 root root 25 8月   8  2020 /usr/bin/gcc-ar-9 -> x86_64-linux-gnu-gcc-ar-9
lrwxrwxrwx 1 root root  8 3月  20  2020 /usr/bin/gcc-nm -> gcc-nm-9
lrwxrwxrwx 1 root root 26 5月  29 15:49 /usr/bin/gcc-nm-10 -> x86_64-linux-gnu-gcc-nm-10
lrwxrwxrwx 1 root root 25 4月   2  2020 /usr/bin/gcc-nm-8 -> x86_64-linux-gnu-gcc-nm-8
lrwxrwxrwx 1 root root 25 8月   8  2020 /usr/bin/gcc-nm-9 -> x86_64-linux-gnu-gcc-nm-9
lrwxrwxrwx 1 root root 12 3月  20  2020 /usr/bin/gcc-ranlib -> gcc-ranlib-9
lrwxrwxrwx 1 root root 30 5月  29 15:49 /usr/bin/gcc-ranlib-10 -> x86_64-linux-gnu-gcc-ranlib-10
lrwxrwxrwx 1 root root 29 4月   2  2020 /usr/bin/gcc-ranlib-8 -> x86_64-linux-gnu-gcc-ranlib-8
lrwxrwxrwx 1 root root 29 8月   8  2020 /usr/bin/gcc-ranlib-9 -> x86_64-linux-gnu-gcc-ranlib-9
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-9 50

sudo update-alternatives --config gcc
There are 2 choices for the alternative gcc (providing /usr/bin/gcc).

  Selection    Path             Priority   Status
------------------------------------------------------------
* 0            /usr/bin/gcc-10   100       auto mode
  1            /usr/bin/gcc-10   100       manual mode
  2            /usr/bin/gcc-9    50        manual mode

Press  to keep the current choice[*], or type selection number: 2
update-alternatives: using /usr/bin/gcc-9 to provide /usr/bin/gcc (gcc) in manual mode

---

don’t know why "main slave "problem

cd /var/lib/dpkg/alternatives/
rm gcc

then install alternative again
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-10 100 --slave /usr/bin/g++ g++ /usr/bin/g+±10 --slave /usr/bin/gcov gcov /usr/bin/gcov-10

then ok