I'm still on Ubuntu 22.04 LTS but needed g++14. The sudo apt-get gcc-14 did not work for me, as it installed clang++14 for some reason (perhaps a misconfiguration on my part). What did work for me was following the instructions I found at https://www.dedicatedcore.com/blog/install-gcc-compiler-ubuntu/

The steps I took:

sudo apt install build-essential
sudo apt install libmpfr-dev libgmp3-dev libmpc-dev -y
wget https://ftp.gnu.org/gnu/gcc/gcc-14.1.0/gcc-14.1.0.tar.gz
tar -xf gcc-14.1.0.tar.gz
cd gcc-14.1.0
./configure -v --build=$(uname -m)-linux-gnu --host=$(uname -m)-linux-gnu --target=$(uname -m)-linux-gnu --prefix=/usr/local/gcc-14.1.0 --enable-checking=release --enable-languages=c,c++ --disable-multilib --program-suffix=-14.1.0
make
sudo make install

And if you would like to make it the default:

sudo update-alternatives --install /usr/bin/g++ g++ /usr/local/gcc-14.1.0/bin/g++-14.1.0 14
sudo update-alternatives --install /usr/bin/gcc gcc /usr/local/gcc-14.1.0/bin/gcc-14.1.0 14

After that, g++ showed I was running version 14.1.0. I was then able to compile my project that included some c++20/23 features that were not in the previous versions of g++ (chrono/format).

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.