如何使用 nlohmann json 解析对象数组？

Question

I have looked through many answers using nlohmann json but I have not found one that works with the below json.

json:

 [{
        "geometry":
        {
            "type": "dd",
            "coordinates":
            [
                [
                    [
                        -156.09375,
                        19.311143355064644
                    ],
                    [
                        -156.09375,
                        19.973348786110606
                    ],
                    [
                        -155.390625,
                        19.973348786110606
                    ],
                    [
                        -155.390625,
                        19.311143355064644
                    ],
                    [
                        -156.09375,
                        19.311143355064644
                    ]
                ]
            ]
        },
        "type": "fdgdsg",
        "properties":
        {},
        "layer":
        {
            "id": "bounding_box",
            "type": "fill",
            "source": "bounding_box_source",
            "paint":
            {
                "fill-color":
                {
                    "r": 0,
                    "g": 0.5333333333333333,
                    "b": 0.5333333333333333,
                    "a": 1
                },
                "fill-opacity": 0.45
            },
            "layout":
            {}
        },
        "source": "bounding_box_source",
        "state":
        {}
    },
    {
        "geometry":
        {
            "type": "yyy",
            "coordinates":
            [
                [
                    [
                        -155.56640625,
                        19.973348786110606
                    ],
                    [
                        -155.390625,
                        19.973348786110606
                    ],
                    [
                        -155.390625,
                        19.311143355064644
                    ],
                    [
                        -155.56640625,
                        19.311143355064644
                    ],
                    [
                        -155.56640625,
                        19.973348786110606
                    ]
                ]
            ]
        },
        "type": "Feature",
        "properties":
        {},
        "layer":
        {
            "id": "bounding_box",
            "type": "fill",
            "source": "bounding_box_source",
            "paint":
            {
                "fill-color":
                {
                    "r": 0,
                    "g": 0.5333333333333333,
                    "b": 0.5333333333333333,
                    "a": 1
                },
                "fill-opacity": 0.45
            },
            "layout":
            {}
        },
        "source": "bounding_box_source",
        "state":
        {}
    }
]

I am using

for (auto& el : j.items())
{
std::cout << el.value() << '\n'
}

This gets the geometry value of all of the objects but how do I access the other fields besides geometry such as layer or properties for each object?

Answer 1

I figured it out I was not setting el.value to it's own object.

Full parsing code:

    json j;
    ifstream ifs(*File);
    if (!ifs.is_open())
    {
        //return false;;
    }
    ifs >> j;
    ifs.close();

    for (auto& elm : j.items())
    {
        nlohmann::json object = elm.value();

        std::cout << object.at("geometry") << std::endl;
        std::cout << object.at("geometry")["type"] << std::endl;
        std::cout << object.at("source") << std::endl;
    }

So object now represents each top-level unnamed object.