安装默认，有时候会出问题。怎么办？查询一下版本：
sudo apt update
sudo apt-cache madison g++
g++ | 4:8.3.0-1 | http://deb.debian.org/debian buster/main amd64 Packages
g++ | 4:6.3.0-4 | https://mirrors.ustc.edu.cn/debian stretch/main amd64 Packages
g++ | 4:6.3.0-4 | https://mirrors.tuna.tsinghua.edu.cn/debian stretch/main amd64 Packages
g++ | 4:6.3.0-4 | https://mirror.sjtu.edu.cn/debian stretch/main amd64 Packages
g++ | 4:6.3.0-4 | http://mirrors.aliyun.com/debian stretch/main amd64 Packages
g++ | 4:6.3.0-4 | https://mirrors.huaweicloud.com/debian stretch/main amd64 Packages
g++ | 4:6.3.0-4 | http://mirrors.163.com/debian stretch/main amd64 Packages
gcc-defaults | 1.168 | https://mirrors.ustc.edu.cn/debian stretch/main Sources
gcc-defaults | 1.168 | https://mirrors.tuna.tsinghua.edu.cn/debian stretch/main Sources
gcc-defaults | 1.168 | https://mirror.sjtu.edu.cn/debian stretch/main Sources
gcc-defaults | 1.168 | http://mirrors.aliyun.com/debian stretch/main Sources
gcc-defaults | 1.168 | https://mirrors.huaweicloud.com/debian stretch/main Sources
gcc-defaults | 1.168 | http://mirrors.163.com/debian stretch/main Sources
gcc-defaults | 1.181 | http://deb.debian.org/debian buster/main Sources
安装低版本：
apt install g++=4:6.3.0-4
