示例代码

//demo.hpp
#pragma once

#include <eosiolib/eosio.hpp>
#include <eosiolib/print.hpp>
#include "json.hpp"
#include <string>

using json = nlohmann::json;
using eosio::contract;
using eosio::multi_index;
using eosio::print;

class[[eosio::contract]] demo : public contract
{
  public:
    using contract::contract;

    [[eosio::action]] void demoaction();
};
//demo.cpp
#include "demo.hpp"
using json = nlohmann::json;

// ACTION
void demo::demoaction()
{
    json demoInfo = R"(
    {
        "demoInfo": {
            "hello": "world"
        }
    }
    )"_json;
    std::string demoInfoString = demoInfo.dump();
    json demoInfoJson = json::parse(demoInfoString);
    print("It worked\n");
}

EOSIO_DISPATCH(demo, (demoaction))

json.hpp从https://github.com/nlohmann/json/releases 下载并将其放在同一目录中demo.hpp。

参考

https://github.com/EOSIO/eosio.cdt/issues/110