forked from mpusz/mp-units
84 lines
2.8 KiB
Markdown
84 lines
2.8 KiB
Markdown
# Code Example
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Here is a small example of operations possible on scalar quantities:
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```cpp
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#include <mp-units/systems/si/si.h>
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using namespace mp_units;
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using namespace mp_units::si::unit_symbols;
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// simple numeric operations
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static_assert(10 * km / 2 == 5 * km);
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// unit conversions
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static_assert(1 * h == 3600 * s);
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static_assert(1 * km + 1 * m == 1001 * m);
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// derived quantities
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static_assert(1 * km / (1 * s) == 1000 * m / s);
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static_assert(2 * km / h * (2 * h) == 4 * km);
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static_assert(2 * km / (2 * km / h) == 1 * h);
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static_assert(2 * m * (3 * m) == 6 * m2);
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static_assert(10 * km / (5 * km) == 2 * one);
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static_assert(1000 / (1 * s) == 1 * kHz);
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```
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!!! example "[Try it on Compiler Explorer](https://godbolt.org/z/81Ev7qhTd)"
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This library requires some C++20 features ([concepts and constraints](https://en.cppreference.com/w/cpp/language/constraints),
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[classes as NTTP](https://en.cppreference.com/w/cpp/language/template_parameters), ...). Thanks to them,
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the user gets a powerful but still easy-to-use interface where all unit conversions and dimensional analysis can be
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performed without sacrificing accuracy. Please see the below example for a quick preview of basic library features:
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*[NTTP]: Non-Type Template Parameter
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```cpp
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#include <mp-units/format.h>
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#include <mp-units/ostream.h>
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#include <mp-units/systems/international/international.h>
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#include <mp-units/systems/isq/isq.h>
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#include <mp-units/systems/si/si.h>
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#include <iostream>
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using namespace mp_units;
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constexpr QuantityOf<isq::speed> auto avg_speed(QuantityOf<isq::length> auto d,
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QuantityOf<isq::time> auto t)
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{
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return d / t;
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}
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int main()
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{
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using namespace mp_units::si::unit_symbols;
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using namespace mp_units::international::unit_symbols;
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constexpr quantity v1 = 110 * km / h;
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constexpr quantity v2 = 70 * mph;
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constexpr quantity v3 = avg_speed(220. * isq::distance[km], 2 * h);
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constexpr quantity v4 = avg_speed(isq::distance(140. * mi), 2 * h);
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constexpr quantity v5 = v3.in(m / s);
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constexpr quantity v6 = value_cast<m / s>(v4);
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constexpr quantity v7 = value_cast<int>(v6);
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std::cout << v1 << '\n'; // 110 km/h
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std::cout << v2 << '\n'; // 70 mi/h
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std::cout << std::format("{}", v3) << '\n'; // 110 km/h
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std::cout << std::format("{:*^14}", v4) << '\n'; // ***70 mi/h****
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std::cout << std::format("{:%Q in %q}", v5) << '\n'; // 30.5556 in m/s
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std::cout << std::format("{0:%Q} in {0:%q}", v6) << '\n'; // 31.2928 in m/s
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std::cout << std::format("{:%Q}", v7) << '\n'; // 31
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}
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```
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!!! example "[Try it on Compiler Explorer](https://godbolt.org/z/Tsesa1Pvq)"
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!!! note
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You can find more code examples in the [Examples](../users_guide/examples/tags_index.md) chapter.
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