mp-units - The quantities and units library for C++

The mp-units library might be the subject of ISO standardization for C++29. More on this can be found in the following ISO C++ proposals:

• P1935: A C++ Approach to Physical Units,
• P2980: A motivation, scope, and plan for a quantities and units library,
• P3045: Quantities and units library.

We are actively looking for parties interested in field-trialing the library.

Documentation

An extensive project documentation can be found on mp-units GitHub Pages. It includes installation instructions and a detailed user's guide.

TL;DR

mp-units is a compile-time enabled Modern C++ library that provides compile-time dimensional analysis and unit/quantity manipulation.

Here is a small example of possible operations:

```cpp

include

using namespace mpunits; using namespace mpunits::si::unit_symbols;

// simple numeric operations static_assert(10 * km / 2 == 5 * km);

// conversions to common units staticassert(1 * h == 3600 * s); staticassert(1 * km + 1 * m == 1001 * m);

// derived quantities staticassert(1 * km / (1 * s) == 1000 * m / s); staticassert(2 * km / h * (2 * h) == 4 * km); static_assert(2 * km / (2 * km / h) == 1 * h);

static_assert(2 * m * (3 * m) == 6 * m2);

static_assert(10 * km / (5 * km) == 2 * one);

static_assert(1000 / (1 * s) == 1 * kHz); ```

Try it on the Compiler Explorer.

This library heavily uses C++20 features (concepts, classes as NTTPs, ...). Thanks to them the user gets a powerful but still easy to use interfaces and all unit conversions and dimensional analysis can be performed without sacrificing on runtime performance or accuracy. Please see the below example for a quick preview of basic library features:

```cpp

include

include

include

include

include

include

include

using namespace mp_units;

constexpr QuantityOfisq::speed auto avg_speed(QuantityOfisq::length auto d, QuantityOfisq::time auto t) { return d / t; }

int main() { using namespace mpunits::si::unitsymbols; using namespace mpunits::international::unitsymbols;

constexpr quantity v1 = 110 * km / h; constexpr quantity v2 = 70 * mph; constexpr quantity v3 = avgspeed(220. * isq::distance[km], 2 * h); constexpr quantity v4 = avgspeed(isq::distance(140. * mi), 2 * h); constexpr quantity v5 = v3.in(m / s); constexpr quantity v6 = valuecast(v4); constexpr quantity v7 = valuecast(v6);

std::cout << v1 << '\n'; // 110 km/h std::cout << std::setw(10) << std::setfill('') << v2 << '\n'; // *70 mi/h std::cout << std::format("{:^10}\n", v3); // 110 km/h std::println("{:%N in %U of %D}", v4); // 70 in mi/h of LT⁻¹ std::println("{::N[.2f]}", v5); // 30.56 m/s std::println("{::N[.2f]U[dn]}", v6); // 31.29 m⋅s⁻¹ std::println("{:%N}", v7); // 31 } ```

Try it on the Compiler Explorer.

Try It Out

The Compiler Explorer

As can be see in the previous chapter, the mp-units library is available in the Compiler Explorer. Use it to get a fast hands-on experience or try some ideas.

GitHub Codespaces

For more advanced development or contributions we encourage you to use our pre-configured GitHub Codespaces environment. You can either click the button below

or navigate to the main page of the repository and click "Code" button -> "Codespaces" tab -> "Create codespace on master".

You can also use the pre-configured devcontainer and Docker image manually within your IDE.

For detailed environment documentation, see .devcontainer/README.md.