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Use C++ Modules and import std

Use C++ Modules and import std

macOS + Clang

Warning

Clang version must be at least 19.

  1. Install tools
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xcode-select --install
brew install llvm cmake ninja

Note

  • The AppleClang version is relatively old. To use the latest features, it is recommended to use the LLVM provided by Homebrew.
  • The import std feature requires Ninja.
  1. Configure the CMake command line
  • Generator: It is recommended to use the latest Multi-Config generator so that Debug and Release configurations can be generated in the same folder.
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-G "Ninja Multi-Config"
  • System standard library (macOS-specific configuration)
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-DCMAKE_OSX_SYSROOT=/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk

Note

  • You can use xcrun --sdk macosx --show-sdk-path to view the exact path.
  • It is recommended to use the system-provided standard library rather than linking to the libc++ and libunwind provided by Homebrew LLVM.
  • JSON file for the std module
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-DCMAKE_CXX_STDLIB_MODULES_JSON=/opt/homebrew/opt/llvm/lib/c++/libc++.modules.json

Note

You can locate the specific path using find /opt/homebrew -name "libc++.modules.json" -maxdepth 10, then rewrite it as /opt/homebrew/opt/llvm/....

  1. Configure CMakeLists.txt
CMakeLists.txt
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cmake_minimum_required(VERSION 4.2)
# Must be set before project(). The specific UUID value changes with the CMake version.
# See:
# https://github.com/Kitware/CMake/blob/<version>/Help/dev/experimental.rst#c-import-std-support
# (Example version: v4.2.3)
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD "d0edc3af-4c50-42ea-a356-e2862fe7a444")
project(example LANGUAGES CXX)

add_executable(example)
# Configure C++23 standard
target_compile_features(example PRIVATE cxx_std_23)
# Enable import std and disable non-standard extensions
set_target_properties(example PROPERTIES
    CXX_MODULE_STD ON
    CMAKE_CXX_EXTENSIONS OFF
)

# Add regular source files
target_sources(example PRIVATE main.cpp)
# Add module files
target_sources(example PRIVATE
    FILE_SET CXX_MODULES FILES foo.cppm
)

Linux + gcc

Warning

gcc version must be at least 15.

Note

Operations not mentioned are exactly the same as on macOS.

  1. Install tools
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sudo apt install g++-15 cmake ninja-build
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sudo dnf install gcc-c++ cmake ninja-build
  1. JSON file for the std module: obtain it with the following command
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g++ -print-file-name=libstdc++.modules.json
  1. Modify CMakeLists.txt
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target_compile_options(example PRIVATE -fmodules)

Windows + MSVC

Warning

MSVC version must be at least 14.36 (equivalent to Visual Studio 2022 v17.6).

The steps are basically the same as macOS, but you do not need to provide CMAKE_CXX_STDLIB_MODULES_JSON.

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