How to install gcc8 using devtoolset-8-gcc

To install the full tools-set including gfortran on centos 7:

yum install centos-release-scl
yum install devtoolset-8
scl enable devtoolset-8 -- bash

enable the tools:

source /opt/rh/devtoolset-8/enable 

you may wish to put the command above in .bash_profile

ref: https://unix.stackexchange.com/questions/477360/centos-7-gcc-8-installation

devtoolset-8 was only released a short while ago. The linked installation instructions may be of use. However, your question pertains to CentOS, and this does not yet appear to have been made available yet. You can see some evidence of it being build for CentOS here, but it's not been updated for the final release yet.

You could ask on the SCL mailing list for an ETA, or wait until it appears in its final form. In the meantime, you could download the RPMs from koji directly.