Installing compilers on macOS

Warning

Apple made the dubious choice when they switched from GNU compilers to AppleClang ones to provide symbolic links that point toward the new compiler. So on a standard installation of macOS if you type in a terminal gcc or g++ the odds are you're in fact using AppleClang... Typing gcc -v will tell you which version you are using!

For most users Apple Clang is fine; getting g++ or LLVM-clang++ is useful for the integration manager to be able to check locally that those compilers are properly supported (and even then CI provides most of those needs - it is only when something is awry than it is practical to be able to check locally).

AppleClang

Apple clang is shipped with XCode; just install XCode from the AppleStore and open it; additional components will be installed at this moment (including development tools such as git command line).
gfortran is typically installed through Homebrew. At the time of this writing this means you need to type:

/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

to install Homebrew and then:

brew install gfortran

to install gfortran.

For a long time gfortran was installed from this website but in the recent years the archives there weren't without issues; using Homebrew is safer.

gcc or clang

Homebrew is your friend here if you want a version of gcc or LLVM-clang on your Mac:

brew install gcc

You may have to change write permissions to install it properly (follow the Homebrew instructions in your Terminal to do so).

Please notice that gcc or g++ will keep pointing to the default ones set up by Apple (see the warning above); you need either to update your path or to explicitly specify the compiler to use, e.g. /usr/local/Cellar/gcc/11.3.0/bin/g++-11 for me at the time of this writing.

Same for clang:

brew install llvm

which installs a version to look at in /usr/local/Cellar (e.g. /usr/local/Cellar/llvm/13.0.1_1/bin/clang++).

Installing GNU compiler on Ubuntu

Compilers and their standard library

It is better to use along with a compiler the companion standard library, which is:

libstdc++ for g++
libc++ for clang++

On Ubuntu it is rather painful to install properly and use libc++ (or at least it was last time I tried...), so the choice was made to only provide guidance for g++ compiler (continuous integration for instance in Gitlab-CI does not cover the Ubuntu/clang configuration for that reason).

gcc

Ubuntu distribution is rather conservative in its compiler version and your Ubuntu is probably shipped with a not very recent gcc.

To install a more recent one (gcc 11 at the time of this writing), type [^1]:

sudo apt-get install --no-install-recommends -y software-properties-common
sudo add-apt-repository ppa:ubuntu-toolchain-r/test && sudo apt-get update \
     && sudo apt-get install -y gcc-11 g++-11 gfortran-11     
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-11 100 --slave /usr/bin/g++ g++ /usr/bin/g++-11 --slave /usr/bin/gfortran gfortran /usr/bin/gfortran-11

and check with

which g++

the correct version is returned.

Running again

sudo update-alternatives --config gcc

allows you to switch back to another version of gcc if need be.

Installing compilers on Fedora

Contrary to Ubuntu, Fedora is shipped with fairly recent versions of compilers; check it but on recent Fedora gcc is already a recent one.

gcc

So the install gcc (and gfortran)[^1]:

dnf --setopt=install_weak_deps=False --best install -y gcc gcc-c++ gcc-gfortran

clang

For clang (and gfortran)[^1]:

dnf --setopt=install_weak_deps=False --best install -y clang libcxx libunwind libcxx-devel gcc-gfortran

[^1]: You may have a look at the companion project Dockerfiles to get the hint of how the compilers were installed for the Docker images used in continuous integration (keep in mind though there are lot of explicit dependencies as a Docker image is bare-bone - if you're using a desktop Linux OS some of the stuff will already be installed).