You should be able to just do yum install gcc-c++ if the repos are set up. Give that a try first (you can see what repos are installed with yum repolist).

Ok, the repository has nothing to do with the workstation sub-channel, it's called rhel-6-desktop-optional-rpms. After I enabled that in the /etc/yum.repos.d/redhat.repo, yum found the gcc-c++ package.

CentOS 8 already comes with GCC 8.

On CentOS 7, you can install GCC 8 from Developer Toolset. First you need to enable the Software Collections repository:

yum install centos-release-scl

Then you can install GCC 8 and its C++ compiler:

yum install devtoolset-8-gcc devtoolset-8-gcc-c++

To switch to a shell which defaults gcc and g++ to this GCC version, use:

scl enable devtoolset-8 -- bash

You need to wrap all commands under the scl call, so that the process environment changes performed by this command affect all subshells. For example, you could use the scl command to invoke a shell script that performs the required actions.

Since the package is either not available, or using a different name, the first step is to find which is the case. Use

yum list available |grep gcc
yum list available |grep devtoolset

to find whether you have misspelled the package name, or if gcc is available under a different name. Check using yum info for the package. Its description should show the relevant version information.

According to Red Hat's article What gcc versions are available in Red Hat Enterprise Linux?, gcc 4.8 is available for Red Hat Enterprise 7. If you need gcc 4.8 for RHEL 6, you may have to compile it yourself.

Further reading:

• Installing GCC 4.8.2 on Red Hat Enterprise linux 6.5
• How to Install gcc 4.7.x/4.8.x on CentOS
• install latest gcc on rhel 6 x86_64