GitHub - cleishm/thermo-cpp: A type-safe, header-only C++23 library for temperature handling, modeled after `std::chrono`

A type-safe, header-only C++23 library for temperature handling, modeled after std::chrono.

Features

Type-safe temperatures with distinct types for Celsius, Kelvin, and Fahrenheit
Configurable precision (degree, decidegree, millidegree)
Automatic conversions between scales and precisions
Lossless implicit conversions (lossy conversions require explicit casts)
Temperature deltas distinct from absolute temperatures
User-defined literals for concise notation
std::format support (when available)
Fully constexpr - all operations can be evaluated at compile time

Requirements

C++23 compiler (GCC 13+, Clang 17+, MSVC 19.36+)
MSVC users: The following compiler flags are required:
- /std:c++latest - Enable C++23 features
- /Zc:__cplusplus - Set __cplusplus macro correctly
- /utf-8 - Treat source files as UTF-8 (for degree symbols)

Installation

CMake FetchContent

include(FetchContent)
FetchContent_Declare(
    thermo
    GIT_REPOSITORY https://github.com/cleishm/thermo-cpp.git
    GIT_TAG v1.0.0
)
FetchContent_MakeAvailable(thermo)

target_link_libraries(your_target PRIVATE thermo::thermo)

vcpkg

vcpkg install cleishm-thermo-cpp

find_package(thermo CONFIG REQUIRED)
target_link_libraries(your_target PRIVATE thermo::thermo)

Manual

Copy the include/thermo/ directory to your project.

Usage

#include <thermo/thermo>  // or <thermo/thermo.hpp>

using namespace thermo;
using namespace thermo_literals;

// Absolute temperatures
celsius room_temp{20};
kelvin absolute = room_temp;  // implicit conversion to higher precision
fahrenheit f = fahrenheit(room_temp);  // explicit cross-scale conversion

// Using literals
auto boiling = 100_c;
auto freezing = 32_f;
auto absolute_zero = 0_k;

// Precision control
millicelsius precise{25500};  // 25.5°C
celsius coarse = celsius(precise);  // explicit lossy conversion (truncates to 25°C)
millicelsius back = coarse;  // implicit lossless conversion (25000 m°C)

// Temperature deltas (differences)
auto delta = 5_Δc;  // 5 degree change
auto new_temp = room_temp + delta;  // 25°C

// Computing differences
delta_celsius diff = difference(boiling, room_temp);  // 80°C difference

// Comparisons work across precisions
if (millicelsius{20000} == celsius{20}) {
    // true - same temperature, different precision
}

// String conversion
std::string s = to_string(room_temp);  // "20°C"

Temperature Types

Absolute Temperatures

Type	Scale	Precision
`celsius`	Celsius	1°C
`decicelsius`	Celsius	0.1°C
`millicelsius`	Celsius	0.001°C
`kelvin`	Kelvin	1 K
`decikelvin`	Kelvin	0.1 K
`millikelvin`	Kelvin	0.001 K
`fahrenheit`	Fahrenheit	1°F
`decifahrenheit`	Fahrenheit	0.1°F
`millifahrenheit`	Fahrenheit	0.001°F

Temperature Deltas

Type	Precision
`delta_celsius` / `delta_kelvin`	1°
`delta_decicelsius` / `delta_decikelvin`	0.1°
`delta_millicelsius` / `delta_millikelvin`	0.001°
`delta_fahrenheit`	1°F (= 5/9°C)
`delta_decifahrenheit`	0.1°F
`delta_millifahrenheit`	0.001°F

Literals

using namespace thermo_literals;

// Absolute temperatures
20_c      // celsius(20)
200_dc    // decicelsius(200) = 20.0°C
20000_mc  // millicelsius(20000) = 20.000°C
293_k     // kelvin(293)
68_f      // fahrenheit(68)

// Temperature deltas
5_Δc      // delta_celsius(5)
5000_Δmc  // delta_millicelsius(5000)
9_Δf      // delta_fahrenheit(9) = delta_celsius(5)

Conversion Rules

Conversions follow the same philosophy as std::chrono:

Implicit conversions are allowed when lossless (e.g., celsius → millicelsius)
Explicit conversions are required when lossy (e.g., millicelsius → celsius)
Cross-scale conversions consider both precision and scale offset

// Implicit (lossless)
millicelsius mc = celsius{20};       // OK: 20°C → 20000 m°C
millikelvin mk = millicelsius{0};    // OK: 0 m°C → 273150 mK

// Explicit required (lossy)
celsius c = celsius(millicelsius{1500});  // 1500 m°C → 1°C (truncates)
kelvin k = kelvin(celsius{0});            // 0°C → 273 K (truncates 273.15)

// Use temperature_cast for explicit conversions
auto k2 = temperature_cast<kelvin>(celsius{100});

Building Tests

cmake -B build -DTHERMO_BUILD_TESTS=ON
cmake --build build
ctest --test-dir build

Building with MSVC

When using MSVC, you must pass the required compiler flags:

cmake -B build -DTHERMO_BUILD_TESTS=ON -DCMAKE_CXX_FLAGS="/std:c++latest /Zc:__cplusplus /utf-8 /EHsc"
cmake --build build --config Release
ctest --test-dir build -C Release

License

MIT License - see LICENSE for details.