C++ 诺依曼json

#include 
#include 
using json = nlohmann::json;

int main()
{
    // create JSON values
    json object = {{"one", 1}, {"two", 2}};
    json null;

    // print values
    std::cout << object << 'n'; // expect {"one":1,"two":2}

    std::cout << null << 'n'; // expect null

    // emplace member function add values, 默认对key进行字典排序
    auto res1 = object.emplace("three", 3);
    null.emplace("A", "a");
    null.emplace("B", "b");

    // the following call will not add an object, because there is already
    // a value stored at key "B"
    auto res2 = null.emplace("B", "c");

    // print values
    std::cout << object << 'n'; // expect {"one":1,"three":3,"two":2}

    // 添加失败，返回值res1.second为false,成功则为true
    std::cout << *res1.first << " " << std::boolalpha << res1.second << 'n'; // 3 true

    std::cout << null << 'n';// expect {"A":"a","B":"b"}
    std::cout << *res2.first << " " << std::boolalpha << res2.second << 'n';// "b" false
}