Module support is experimental. This page shows two complete programs that use import cli11;. For the build options, targets, and requirements, see Modulesin the installation chapter". @section a-complete-minimal-project A complete minimal project Build and install CLI11 with <tt>-DCLI11_MODULES=ON</tt> first, then use this project: @icode{cmake} cmake_minimum_required(VERSION 3.28) project(myapp LANGUAGES CXX) set(CMAKE_CXX_STANDARD 20) set(CMAKE_CXX_STANDARD_REQUIRED ON) find_package(CLI11 REQUIRED) add_executable(myapp myapp.cpp) target_link_libraries(myapp PRIVATE CLI11::Module) @endicode @icode{cpp} // myapp.cpp // Keep the includes before the import; GCC rejects the reverse order. #include <iostream> #include <string> import cli11; int main(int argc, char *argv[]) { CLI::App app{"MyApp"}; std::string file; app.add_option("-f,--file", file, "The file name")->required(); try { app.parse(argc, argv); } catch(const CLI::ParseError &e) { return app.exit(e); } std::cout << "file=" << file << '\n'; return 0; } @endicode Use the same compiler for the CLI11 library and the application. Macros such as <tt>CLI11_PARSE</tt> are not available through <tt>import cli11;</tt> — use <tt>app.parse()</tt> and catch <tt>CLI::ParseError</tt>, or include the headers as well. @section use-with-import-std Use with import std You can combine <tt>import cli11;</tt> with <tt>import std;</tt>. This needs C++23 and a standard library that ships the <tt>std</tt> module (recent libc++, MSVC, or libstdc++ from GCC 15+). CMake support for <tt>import std</tt> (<tt>CMAKE_CXX_MODULE_STD</tt>, CMake 3.30+) is experimental and is behind the <tt>CMAKE_EXPERIMENTAL_CXX_IMPORT_STD</tt> gate, so this example invokes clang and libc++ directly: @icode{cpp} // myapp.cpp import cli11; import std; int main(int argc, char *argv[]) { CLI::App app{"MyApp"}; std::string file; app.add_option("-f,--file", file, "The file name")->required(); try { app.parse(argc, argv); } catch(const CLI::ParseError &e) { return app.exit(e); } std::println("file={}", file); return 0; }

# CLI11 = path to the CLI11 sources, LIBCXX = path that contains std.cppm
# (for example <llvm prefix>/share/libc++/v1)
clang++ -std=c++23 -O2 -Wno-reserved-module-identifier --precompile \
    $LIBCXX/std.cppm -o std.pcm
clang++ -std=c++23 -O2 -Wno-reserved-module-identifier -c std.pcm -o std.o
clang++ -std=c++23 -O2 -DCLI11_COMPILE -I $CLI11/include --precompile \
    $CLI11/src/modules/CLI11.cppm -o cli11.pcm
clang++ -std=c++23 -O2 -c cli11.pcm -o cli11.o
clang++ -std=c++23 -O2 -DCLI11_COMPILE -I $CLI11/include \
    -c $CLI11/src/Precompile.cpp -o impl.o
clang++ -std=c++23 -O2 -fmodule-file=std=std.pcm \
    -fmodule-file=cli11=cli11.pcm -c myapp.cpp -o myapp.o
clang++ myapp.o cli11.o impl.o std.o -o myapp

With both modules prebuilt, only the last two commands run again when myapp.cpp changes, and they are fast; in our tests the application compiled several times faster than an equivalent header-only build. Exact times depend on the compiler and the application.