"hello, world" with C++ modules

What we need

• clang 17 = https://en.cppreference.com/w/cpp/compiler_support
• cmake 3.28 = https://cmake.org/cmake/help/latest/manual/cmake-cxxmodules.7.html
• Ninja 1.11

The next version of Ubuntu, Noble Numbat (which will be 24.04 http://cdimage.ubuntu.com/daily-live/pending/) comes with the versions we need. To check the content of the packages, see https://packages.ubuntu.com/

Dockerfile

We use ubuntu:noble as the base image. We add the packages for the tools listed above.

We add gdb to be compatible with CLion and clang-tools to get clang-scan-deps. The link avoid an error like /bin/sh: 1: CMAKE_CXX_COMPILER_CLANG_SCAN_DEPS-NOTFOUND: not found. See https://stackoverflow.com/questions/77800212/clang-scan-deps-was-not-found-while-trying-to-build-c-20-modules

Build Docker image

docker build --tag cxx_modules .

Execute "hello, world"

By hand

Just for fun, let's build the project without CMake.

Get a shell inside the container:

docker run --rm -it -v $(pwd):/cxx_modules cxx_modules

From the container:

cd cxx_modules
clang++ -std=c++20 helloworld.cppm --precompile -o helloworld.pcm
clang++ -std=c++20 main.cpp -fmodule-file=helloworld=helloworld.pcm helloworld.pcm
./a.out

This prints hello, world (with a module).

With CMake

With CMake, it's much easier. Easier :

• configure CLion to use a Docker toolchain: https://www.jetbrains.com/help/clion/clion-toolchains-in-docker.html
  • manually set "Build Tool" / "C Compiler" / "C++ Compiler" to "ninja", "clang", "clang++"
• or use a shell inside the container to build the project like any CMake project

We will get the same output to the console.