SI++

Single header compile-time dimensional analysis library powered by C++20 concepts.

Getting started

All the functionality is provided by the sipp.hpp header.

1. Creating basic units

To create first building blocks of a unit system, basic types have to be defined first.

struct mass_b : sipp::basic_unit{};
using mass = sipp::unit_base<double, sipp::quantity<mass, 1>>;

mass_b in this example is an arbitrarily chosen name for an underlying unit type and mass is the actual type that you will be using. If SIPP_HELPERS is defined SI++ enables a macro SIPP_BASIC_TYPE(BASE, NAME) which accomplishes the same goal.

SIPP_BASIC_TYPE(double, mass);

2. unit_base and quantity

quantity is a quantitative measure of every unit, it represents a unit raised to some non-zero power P, so the template takes two parameters: unit instance and an integer. unit_base represents the units, the first argument is the underlying type of a unit(only arithmetic types are allowed), while the rest are the quantities the unit consists of. The order of quantities or their partitioning does not matter.

3. Derived unit declaration

Units can be defined in terms of other units, there are two ways to do it. Using an explicit instance

using velocity = sipp::unit_base<double, sipp::quantity<distance, 1>, sipp::quantity<time, -1>>; // velocity = distance^1 * time^-1

Or using a decltype

using velocity = decltype(distance{} / time{});

Units can be nested inside other units and are not limited only to the basic types.

4. Operators

unit_base has all the expected operators for an arithmetic type(including implicit casts to arithmetic types). Multiplication and division can be performed on units of any type and on any arithmetic types. The rest of binary operators, including comparison, can only be performed on units of equivalent tupes or arithmetic types.

5. Utility

unit_cast - casts any unit U₁ to unit U₂. Same usage pattern as static_cast.
unit_to_pow - raises unit U to an integer power P. Note that this only produces a type and does not raise the value of the unit to that power.