qtty-cpp

qtty-cpp is a C++17 library for working with physical quantities using unit-safe types. It provides a header-only C++ API backed by the Rust qtty-ffi conversion engine (via a C FFI).

Features

• Strong types per unit (e.g., Meter, Second) to prevent mixing incompatible dimensions
• Unit conversion via Quantity::to<T>() using the Rust qtty-ffi engine
• User-defined literals for convenient construction (e.g., 10.0_km, 5.0_s)
• Generated unit/type/literal headers derived from qtty/qtty-ffi/include/qtty_ffi.h
• CMake target (qtty_cpp) for straightforward integration

Requirements

• CMake 3.15+
• C++17 compiler (GCC 7+, Clang 5+, MSVC 2017+)
• Python 3.6+ (wrapper generation)
• Rust/Cargo (builds qtty-ffi)

Build and Test

git clone --recurse-submodules <repo-url>
cd qtty-cpp

cmake -S . -B build
cmake --build build --parallel
ctest --test-dir build --output-on-failure
./build/demo

If you cloned without submodules:

git submodule update --init --recursive

Usage

#include <iostream>
#include "qtty/qtty.hpp"

using namespace qtty;

int main() {
    auto distance = 100.0_km;
    auto time = 2.0_h;

    auto speed = distance / time; // compound type (e.g., KilometerPerHour)
    std::cout << speed.value() << " km/h\n";

    Meter m = distance.to<Meter>();
    std::cout << m.value() << " m\n";
}

Compound Units

Division creates compound quantity types (e.g., velocity). The FFI conversion layer only supports base dimensions, so compound types cannot be converted directly (for example, m/s to km/h). See include/qtty/units/velocity.hpp and docs/architecture.md.

Documentation

• docs/README.md (documentation index)
• docs/QUICK_REFERENCE.md (one-page usage summary)
• docs/api/quantities.md (API reference)
• docs/build-and-testing.md (build, test, troubleshooting)
• docs/extending-units.md (adding units)
• docs/architecture.md (design overview)

Integration

Add as a Subdirectory

add_subdirectory(path/to/qtty-cpp)
target_link_libraries(your_target PRIVATE qtty_cpp)

Install and Use find_package

cmake --install build

find_package(qtty_cpp REQUIRED)
target_link_libraries(your_target PRIVATE qtty::qtty_cpp)

License

This repository wraps the upstream qtty project (git submodule in qtty/). See qtty/LICENSE for licensing details.