JSON / C++ object schema

Convert a schema, written in YAML to a C++ struct hierarchy boilerplate that can be serialized and deserialized. Generates structs and the necessary serialization functions to work seamlessly with nlohmann/json.

In particular class hierarchies, whose objects are serialized to a flat json object is something needed in some contexts, so having the tedious mapping to C++ done with a code generator is nice.

YAML Schema

A struct is defined with a name and properties. The properties have types, of which the basic types are integer, boolean and string.

TextDocument:
  url: string
  bytes: integer

You can use defined types then in other structs; here we use the TextDocument type defined above. If we don't know the type or just want to store plain json, the type object can be used. All of these are stored by value.

Repeated (vector) fields can be marked with a + at the end of the property name.

ReadingList:
  to_read+: TextDocument
  other: object

Structs can be inherited; you can do this by using <: SuperClass in the property field. Optional fields are indicated with a ? at the end of the property name.

OptionallyVersionedTextDocument:
  <: TextDocument
  version?: integer

You can combine + and ? for optional repeated fields. A non-optional repeated field is always serialized while an optional field will not show up in the JSON output if it is not set (the availableness of an optional field is indicated with an has_* flag, so here has_version.

If need be, even multiple inheritance works by adding additional <:.

Generated code

The output are structs with each of the properties stored by value; repeated fields are std::vector<theType>. Also the necessary boilerplate is generated to seamlessly convert the types to and from json with nlohmann/json.

Here is a tiny example, for more check out the example/ dirctory.

  nlohmann::json in_json = { { "url", "https://github.com/hzeller/jcxxgen"},
                             { "bytes", 12345 } };
  TextDocument td = in_json;  // Automatic conversion from json to object

Usage

Input is the yaml schema file, output is a c++ header file.

usage: jcxxgen [options] <protocol-spec-yaml>
Options:
  -o <filename>     : Output to filename
  -j <json-include> : Include path to json.hpp, including brackets <> or quotes "" around.
                      Default: '<nlohmann/json.hpp>'

Work in Progress

Note, this is work in progress, things might change.