peelo-json

I recently stumbled across an Hacker News post that announced an alternative to the widely used nlohmann JSON library for C++.

It gave me an idea to test how much work it would be to write a minimal JSON parser library for C++ and this is the result.

I wanted to be as tiny as possible, not to include it's own UTF-8 decoder (bring your own) and not to throw exceptions but use result type instead.

Doxygen generated API documentation.

Dependencies

This library depends on another header only library called peelo-result. This should be handled by CMake.

Usage

Parsing JSON

You can use peelo::json::parse() function to parse an Unicode string into JSON value.

#include <iostream>
#include <peelo/json.hpp>

int
main()
{
  const auto result = peelo::json::parse(U"[1, 2, 3]");

  if (result)
  {
    if (peelo::json::type_of(*result) == peelo::json::type::array)
    {
      const auto array = peelo::json::as<peelo::json::array>(*result);

      std::cout << "Given input produced an array." << std::endl;
      std::cout << "It has " << array->elements().size() << " elements." << std::endl;
    }
  } else {
    std::cout << "Parsing error occurred: " << result.error().what() << std::endl;
  }
}

If you want specicially to parse an JSON object, you can use peelo::json::parse_object() function instead, which does not accept any other input than an object.

Formatting JSON

To format an JSON value returned by peelo::json::parse() function into an ASCII string, you can use peelo::json::format() function.

#include <iostream>
#include <peelo/json.hpp>

int
main()
{
  if (const auto result = peelo::json::parse(U"{\"foo\": \"bar\"}"))
  {
    // This should output `{"foo":"bar"}` to standard output.
    std::cout << peelo::json::format(*value) << std::endl;
  }
}

TODO

• Pretty print option for formatting JSON values.
• std::u32string version of format() function.