json5

json5 is a small header only C++ library for parsing JSON or JSON5 data. It also comes with a simple reflection system for easy serialization and deserialization of C++ structs.

Quick Example:

#include <json5/json5_input.hpp>
#include <json5/json5_output.hpp>

struct Settings
{
  int x = 0;
  int y = 0;
  int width = 0;
  int height = 0;
  bool fullscreen = false;
  std::string renderer = "";

  JSON5_MEMBERS(x, y, width, height, fullscreen, renderer)
};

Settings s;

// Fill 's' instance from file
json5::FromFile("settings.json", s);

// Save 's' to file
json5::ToFile("settings.json", s);

json5.hpp

Provides the basic types of json5::Document, json5::Value, and json5::IndependentValue. A Value represents a value within JSON but it relies on a Document for storage of non-primitive (string, array, object) data. A Value may be more difficult to manipulate which is why the IndependentValue is provided. An IndependentValue is self-contained and indepenedent of any other object. It contains a variant which respresents all possible JSON value types. Parsing is faster with a Document than with an IndependentValue due to its compact nature and small number of memory allocations.

json5_input.hpp

Provides functions to load json5::Document or json5::IndependentValue from string, stream or file.

json5_output.hpp

Provides functions to convert json5::Document or json5::IndependentValue into string, stream or file.

json5_builder.hpp

Defines Builders for building Documents and IndependentValues. Also provides the basis for building arbitrary objects via reflection.

json5_reflect.hpp

Provides functionality to read/write structs/classes from/to a string, stream, or file

Basic supported types:

• bool
• int, float, double, and other numeric types
• std::string
• std::vector, std::array, std::map, std::unordered_map, std::array
• C array

Reading from JSON

Reading is accomplished via the templated class json5::detail::Reflector. A custom deserializer can be made via a template specialiaztion (or partial specialization) for the class type. Often one would want to inherit json5::detail::RefReflector which holds a reference to the target object. Then override the relevant functions in json5::detail::BaseReflector. This is works because Parser will parse the JSON, calling functions on ReflectionBuilder which uses a stack of BaseReflector objects as it parses depth first into an object. Writing is accomplished via the templated struct json5::detail::ReflectionWriter. A custom serialization should create a template specialization (or partial specialiaztion) for this struct and implement static inline void Write(Writer& w, const T& in) with the proper value for T (in need not be a const ref but could instead take by value like is done when serializing numbers but non-primitives likely should be const ref). This was changed from a templated function becuase partial specializations are not possible with functions but are possible with structs.

json5_base.hpp

Contains Error definitions, ValueType enum, and macro definitions.

json5_filter.hpp

FAQ

TBD

Additional examples

Serialize custom type:

// Let's have a 3D vector struct:
struct Vec3
{
  float x, y, z;
};

// Let's have a triangle struct with 'vec3' members
struct Triangle
{
  vec3 a, b, c;
};

JSON5_CLASS(Triangle, a, b, c)

namespace json5::detail {
  // Write Vec3 to JSON array
  template <>
  class ReflectionWriter<Vec3> : public TupleReflectionWriter<float, float, float>
  {
  public:
    static inline void Write(Writer& w, const Vec3& in) { TupleReflectionWriter::Write(w, in.x, in.y, in.z); }
  };

  // Read Vec3 from JSON array
  template <>
  class Reflector<Vec3> : public TupleReflector<float, float, float>
  {
  public:
    explicit Reflector(Vec3& vec)
      : TupleReflector(vec.x, vec.y, vec.z)
    {}
  };

  // Write Triangle as JSON array of 3 numbers
  template <>
  class ReflectionWriter<Triangle> : public TupleReflectionWriter<Vec3, Vec3, Vec3>
  {
  public:
    static inline void Write(Writer& w, const Triangle& in) { TupleReflectionWriter::Write(w, in.a, in.b, in.c); }
  };

  // Read Triangle from JSON array
  template <>
  class Reflector<Triangle> : public TupleReflector<Vec3, Vec3, Vec3>
  {
  public:
    explicit Reflector(Triangle& tri)
      : TupleReflector(tri.a, tri.b, tri.c)
    {}
  };
} // namespace json5::detail

Serialize enum:

enum class MyEnum
{
  Zero,
  First,
  Second,
  Third
};

// (must be placed in global namespce, requires C++20)
JSON5_ENUM(MyEnum, Zero, First, Second, Third)