Converting to data structure using from_json

Question

I have the below program where I am trying to parse one json into a structure. See that I am the structure Address which I am trying to load from the json string.

However there is some exception.

#include <string>
#include <nlohmann/json.hpp>

using nlohmann::json;

struct Address
{
    std::string houseNo;
    std::string street;
    std::string city;
    std::string postalCode;
    std::string country;
};

void from_json(const json& j, Address& address)
{
    j.at("house").get_to(address.houseNo);
    j.at("street").get_to(address.street);
    j.at("street").get_to(address.street);
    j.at("city").get_to(address.city);
    j.at("postalCode").get_to(address.postalCode);
    j.at("country").get_to(address.country);
}

int main()
{
    std::string str =
            "{\
                \"address\": {\
                        \"city\": \"XYZ\",\
                        \"country\": \"country\",\
                        \"house\": \"123\",\
                        \"postalCode\": \"123456\",\
                        \"street\": \"St. ABC\"\
                    }\
            }";

    json j = json::parse(str);
    printf("[UT_JsonTest] Input json string : \n %s \n", j.dump(4).c_str());
    auto a = j.get<Address>(); //exception here!
}

What is going on wrong here? I see the below output.

> [UT_JsonTest] Input json string :   {
>     "address": {
>         "city": "XYZ",
>         "country": "country",
>         "house": "123",
>         "postalCode": "123456",
>         "street": "St. ABC"
>     } }  unknown file: Failure C++ exception with description "[json.exception.out_of_range.403] key 'house' not found" thrown in
> the test body.

My guess is that `j.get
()` is trying to parse the *outer* object, which have only the `"address"` property. You need to get the `"address"` object first. — Some programmer dude, Mar 05 '21 at 06:33

score 0 · Answer 1 · answered Mar 05 '21 at 06:40

Thanks for the quick hint! I had to pick the "address" value before parsing it!

    std::string str =
            "{\
                \"address\": {\
                        \"city\": \"XYZ\",\
                        \"country\": \"country\",\
                        \"house\": \"123\",\
                        \"postalCode\": \"123456\",\
                        \"street\": \"St. ABC\"\
                    }\
            }";

    json j = json::parse(str);
    printf("[UT_JsonTest] Input json string : \n %s \n", j.dump(4).c_str());
    auto address = j.at("address").get<Address>();

    printf("[UT_JsonTest] address.city = %s\n", address.city.c_str());

Converting to data structure using from_json

1 Answers1