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cpp-json

reflection in c++ for compile-time json de/serialization implemented as a single header library. requires c++20. Works with g++ on macos and linux. Other operating systems & compilers are untested and may not work.

std::string serializedJson = json::serialize(myStruct);
MyStruct deserialized = json::deserialize<MyStruct>(serializedJson);

public domain

do whatever you want with this header file. use it, modify it, sell it. you do not need to credit me in any way.

supported datatypes:

  • strings: std::string, const char * and char *
  • arrays: std::vector, and T[]
  • maps: std::map and std::unordered_map
  • pointers: T*, std::unique_ptr
  • all arithmetic types (int, unsigned long long, double, char, etc)
  • various STL types: std::tuple, std::pair, std::optional, std::queue, std::deque, std::list, std::set, std::unordered_set
  • enums
  • classes and structs via REFLECT
  • can be extended via template specializations.

freeing pointers

if you are smart and use std::vector, std::unique_ptr, and std::string, then you don't need to worry about memory management. you can skip this section.

pointers are not treated as arrays. they are expected to reference a single value. when populating a pointer with json::deserialize(), the data is created using new and so should be freed with delete. const char * and char * are treated differently. they are expected to point to strings. they are created using new [] and so should be deleted with delete [].

exceptions

if any problems occur during serialization or deserialization, a json::exception is thrown. the json::exception is a struct containing a short description in std::string desc and the json index where it was located in int idx.

example usage with serializing/deserializing structs

#include <iostream>
#include "json.hpp"

struct Person {
    std::string name;
    int age;
    std::vector<std::string> friends;
};

// use the REFLECT() macro to make the json serializer aware of the Person type
REFLECT(Person, name, age, friends);

int main() {
    Person person = {"joe", 20, {"ben", "sam"}};

    // create a json string representing the person    
    std::string personJson = json::serialize(person);

    // prettify and print the json string to stdout
    json::Prettifier prettifier;
    std::cout << prettifier.prettify(personJson) << std::endl;

    // construct a new person from the person json
    Person person2 = json::deserialize<Person>(personJson);

    std::cout << person2.name << std::endl;

    return 0;
}

design decisions

  • the json::Prettifier class is used for prettifying the json, instead of having the prettifying capability built into the json::serialize() function. this is to keep the json::serialize() signature simple. You can create your own json::serialize() function specializations from outside of the header file. the signature is simply std::string json::serialize(const T& item); (very beautiful).
  • enums are treated as integers. this seems to be common practice and i do not want to force the user to uglify their enum declarations just so reflection works.
  • only public fields can be serialized. this is also common practice yet you can normally force them to be serialized. i do not see the point of allowing private fields to be serialized since it breaks the idea of encapsulation.