The mp-units library might be the subject of ISO standardization for C++29. More on this can be found in ISO C++ paper P1935. We are actively looking for parties interested in field trialing the library.
A brief introduction to the library's interfaces and the rationale for changes in the version 2.0 of mp-units were provided in detail by Mateusz Pusz in the "mp-units: Lessons Learned and a New C++ Library Design" talk at the ACCU 2023 conference.
An extensive project documentation can be found on mp-units GitHub Pages. It includes installation instructions and a detailed user's guide.
This project uses the official metrology vocabulary defined by the ISO and BIPM. Please familiarize yourself with those terms to better understand the documentation and improve domain-related communication and discussions. You can find essential project-related definitions in our documentation's "Glossary" chapter. Even more terms are provided in the official vocabulary of the ISO and BIPM.
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:
#include <mp-units/systems/si/si.h>
using namespace mp_units;
using namespace mp_units::si::unit_symbols;
// simple numeric operations
static_assert(10 * km / 2 == 5 * km);
// unit conversions
static_assert(1 * h == 3600 * s);
static_assert(1 * km + 1 * m == 1001 * m);
// derived quantities
inline constexpr auto kmph = km / h;
static_assert(1 * km / (1 * s) == 1000 * (m / s));
static_assert(2 * kmph * (2 * h) == 4 * km);
static_assert(2 * km / (2 * kmph) == 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:
#include <mp-units/format.h>
#include <mp-units/ostream.h>
#include <mp-units/systems/international/international.h>
#include <mp-units/systems/isq/isq.h>
#include <mp-units/systems/si/si.h>
#include <iostream>
using namespace mp_units;
constexpr QuantityOf<isq::speed> auto avg_speed(QuantityOf<isq::length> auto d,
QuantityOf<isq::time> auto t)
{
return d / t;
}
int main()
{
using namespace mp_units::si::unit_symbols;
using namespace mp_units::international::unit_symbols;
constexpr quantity v1 = 110 * (km / h);
constexpr quantity v2 = 70 * mph;
constexpr quantity v3 = avg_speed(220. * isq::distance[km], 2 * h);
constexpr quantity v4 = avg_speed(isq::distance(140. * mi), 2 * h);
constexpr quantity v5 = v3.in(m / s);
constexpr quantity v6 = value_cast<m / s>(v4);
constexpr quantity v7 = value_cast<int>(v6);
std::cout << v1 << '\n'; // 110 km/h
std::cout << v2 << '\n'; // 70 mi/h
std::cout << std::format("{}", v3) << '\n'; // 110 km/h
std::cout << std::format("{:*^14}", v4) << '\n'; // ***70 mi/h****
std::cout << std::format("{:%Q in %q}", v5) << '\n'; // 30.5556 in m/s
std::cout << std::format("{0:%Q} in {0:%q}", v6) << '\n'; // 31.2928 in m/s
std::cout << std::format("{:%Q}", v7) << '\n'; // 31
}
Try it on the Compiler Explorer.