Cracon, Craft your configuration!

Cracon is a lightweight C++ library for handling JSON configuration files. It provides a simple and intuitive API for reading, writing configurations. It outputs two files, one default with all defaults parameters set in the code, and one for changed parameters.

It supports (tested for):

• booleans
• enums
• (u)int(00)_t
• float/double
• std::vector
• std::string
• std::array

Most of the heavy lifting is done by Niels Lohmann's awesome JSON library.

Features

• Easy to use
• Somewhat Type-safe (it is still JSON)
• JSON format to be human readable
• Defaults are defined in the code
• Defaults are reported to allow review of the defaults in CI/CD
• Defaults are not mangled to the actual configuration to allow to modify defaults who were not explicitly modified
• Only variations are in the json file

Build & test

# For Linux
git clone https://github.com/AlexisTM/cracon
mkdir cracon/build && cd cracon/build
cmake .. -DCMAKE_BUILD_TYPE=Release -DBUILD_TESTING=ON
cmake --build .
# For Windows
cmake --build . --config Release

ctest

API

Basic usage

auto config = cracon::File("config.json", "defaults.json");
// Or config.init("config.json", "defaults.json")

int int_value = config.get("/int", 1);
auto some_string = config.get<std::string>("/oh/hi", "mark");
auto a_vector = config.get<std::vector<float>>("/vector", {1., 2., 3.});

int_value = config.set("/int", 42);
if(config.should_write()) { // Only write it if there is a change
  config.write();
}

Will result in:

// "defaults.json"
{
  "int": 1,
  "oh": { "hi": "mark" },
  "data": [1.0, 2.0, 3.0]
}

// config.json
{
  "int": 42,
}

Parameters and groups

Groups avoids typos when repeating the same namespace multiple times. Parameters wraps a value to use a single line to read/write a parameter and avoids repeating the accessor/key.

Both groups and parameters keep a shared_ptr to the File, which is initially created by the SharedFile.

class Car {
 public:
  Car(cracon:: SharedFile:: Group config) {

    speed = config.get_param<int64_t>("speed", 9000);
    horsepower = config.get_param<int64_t>("horsepower", 120);
    motor_curve = config.get_param<std::array<int, 24>>("motor_curve", {});

  }

  cracon:: SharedFile:: Param<int64_t> speed;
  cracon:: SharedFile:: Param<int64_t> horsepower;
  cracon:: SharedFile:: Param<std::array<int, 24>> motor_curve;
};

int main() {
  auto config = cracon:: SharedFile("config.json", "defaults.json");
  Car car = Car(config.get_group("car"));
  car.speed.set(1000);
  config.write();
}

Debugging

Build this project with -DCRACON_ENABLE_LOG=ON to enable logging.

$ ./cracon_basic_usage.exe
[cracon] [INFO] The requested key doesn't exist for /oh/hi defaulted to "mark". Error: [json.exception.out_of_range.403] key 'oh' not found
[cracon] [INFO] The requested key doesn't exist for /vector defaulted to [1.0, 2.0, 3.0]. Error: [json.exception.out_of_range.403] key 'vector' not found

Integration in your project

This library uses CPM.cmake for dependency management. This permits many other usage, see examples/cmake... for different integrations.

include(cmake/CPM.cmake)
CPMAddPackage(
  NAME cracon
  GITHUB_REPOSITORY alexistm/cracon
  GIT_TAG main
  VERSION 0.0.1
  OPTIONS "BUILD_EXAMPLES OFF" "BUILD_TESTING OFF"
)

add_executable(${PROJECT_NAME} main.cpp)
target_include_directories(${PROJECT_NAME} PUBLIC
  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
  $<INSTALL_INTERFACE:include>)

target_link_libraries(${PROJECT_NAME} cracon)

install(
  TARGETS ${PROJECT_NAME}
  EXPORT export_${PROJECT_NAME}
  ARCHIVE DESTINATION lib
  LIBRARY DESTINATION lib
  RUNTIME DESTINATION bin
)

Considerations

• If File::get is called multiple times, only the last call defines the default. Call File::get once for consistency or use Param::get which won't reparse the data each time. This check was not added as it increases the overhead significantly if it is called often/big configuration files.
• set does not write to the defaults

Contributing

Contributions to Cracon are welcome! Feel free to open issues, submit pull requests, or provide feedback. Especially if you are a CMake Guru and knows how to ensure this is as easy to integrate as possible.

License

Cracon is released under the MIT License. See the LICENSE file for details.