Cpp: JSON parser in Cpp that provide support Serialize/Deserialize feature, converting JSON objects to user-defined classes?

Question

I\'m working on native C++ development and looking for JSON parser that can handle complex JSON files and convert into class objects.

1. I\'ve looked at native be

Answer 1

jsoncons, nlohmann and ThorsSerializer all support conversion between JSON and C++ objects. Examples with jsoncons and nlohmann are shown below, Martin York has one for his ThorsSerializer in a separate posting. The latter in my opinion is very nice, and certainly wins the prize for brevity. In the spirit of Oscar Wilde's quote that "imitation is the sincerest form of flattery", I've introduced the macro JSONCONS_ALL_MEMBER_TRAITS to jsoncons, and modified that example accordingly.

Consider

const std::string s = R"(
[
    {
        "author" : "Haruki Murakami",
        "title" : "Kafka on the Shore",
        "price" : 25.17
    },
    {
        "author" : "Charles Bukowski",
        "title" : "Pulp",
        "price" : 22.48
    }
]
)";

namespace ns {
    struct book
    {
        std::string author;
        std::string title;
        double price;
    };
} // namespace ns

Using jsoncons to convert between s and an std::vector:

#include 

namespace jc = jsoncons;

// Declare the traits. Specify which data members need to be serialized.
JSONCONS_ALL_MEMBER_TRAITS(ns::book,author,title,price);

int main()
{
    std::vector book_list = jc::decode_json>(s);

    std::cout << "(1)\n";
    for (const auto& item : book_list)
    {
        std::cout << item.author << ", " 
                  << item.title << ", " 
                  << item.price << "\n";
    }

    std::cout << "\n(2)\n";
    jc::encode_json(book_list, std::cout, jc::indenting::indent);
    std::cout << "\n\n";
}

Output:

(1)
Haruki Murakami, Kafka on the Shore, 25.17
Charles Bukowski, Pulp, 22.48

(2)
[
    {
        "author": "Haruki Murakami",
        "price": 25.17,
        "title": "Kafka on the Shore"
    },
    {
        "author": "Charles Bukowski",
        "price": 22.48,
        "title": "Pulp"
    }
]

Using nlohmann to convert between s and an std::vector:

#include 
#include 

namespace nh = nlohmann;

// Provide from_json and to_json functions in the same namespace as your type   
namespace ns {
    void from_json(const nh::json& j, ns::book& val) 
    {
        j.at("author").get_to(val.author);
        j.at("title").get_to(val.title);
        j.at("price").get_to(val.price);
    }

    void to_json(nh::json& j, const ns::book& val) 
    {
        j["author"] = val.author;
        j["title"] = val.title;
        j["price"] = val.price;
    }
} // namespace ns

int main()
{
    nh::json j = nh::json::parse(s);

    std::vector book_list = j.get>();
    std::cout << "\n(1)\n";
    for (const auto& item : book_list)
    {
        std::cout << item.author << ", " 
                  << item.title << ", " 
                  << item.price << "\n";
    }

    std::cout << "\n(2)\n";
    nh::json j2 = book_list;
    std::cout << std::setw(4) << j2 << "\n\n";
}

Output:

(1)
Haruki Murakami, Kafka on the Shore, 25.17
Charles Bukowski, Pulp, 22.48

(2)
[
    {
        "author": "Haruki Murakami",
        "price": 25.17,
        "title": "Kafka on the Shore"
    },
    {
        "author": "Charles Bukowski",
        "price": 22.48,
        "title": "Pulp"
    }
]