在centos8下安装g++，只需输入
yum install gcc gcc-c++
遇到问题：
Errors during downloading metadata for repository ‘testing-devtools-2-centos-8’:
- Status code: 404 for https://people.centos.org/tru/devtools-2/8/x86_64/RPMS/repodata/repomd.xml (IP: 104.206.99.124)
Error: Failed to download metadata for repo ‘testing-devtools-2-centos-8’: Cannot download repomd.xml: Cannot download repodata/repomd.xml: All mirrors were tried
解决方法：
cd /etc/yum.repos.d 修改devtools-2.repo后缀名为devtools-2.Beirepo
再执行
yum clean all yum makecache
[root@iZuf620w89xusfhzridyarZ yum.repos.d]# yum clean all
48 files removed
[root@iZuf620w89xusfhzridyarZ yum.repos.d]# yum makecache
CentOS Linux 8 - AppStream 5.2 MB/s | 9.3 MB 00:01
CentOS Linux 8 - baseOS 2.5 MB/s | 7.5 MB 00:03
CentOS Linux 8 - Extras 7.9 kB/s | 10 kB 00:01
Extra Packages for Enterprise L 46 MB/s | 10 MB 00:00
metadata cache created.
此时再执行yum install gcc gcc-c++为成功
参考链接：https://blog.csdn.net/robertkun/article/details/8466700
