Converting json to structure with char* types

[kevinmoloney7]

I have the following code which works fine with a basic stucture containing an int and std::string types. I have made a custom helper to convert the raw json to my structure type.

#include <iomanip>
#include <iostream>
#include <nlohmann/json.hpp>

struct test {
    int num;
    std::string value_one;
    std::string value_two;
    std::string value_three;
};
void from_json(const nlohmann::json& j, test& p) {
    j.at("amount").get_to(p.num);
    j.at("value1").get_to(p.value_one);
    j.at("value2").get_to(p.value_two);
    j.at("value3").get_to(p.value_three);
}

auto check(test& response_body, const std::string& resp) -> bool {
    nlohmann::json payment_body{};
    {
        nlohmann::json j1 = nlohmann::json::parse(resp);
        payment_body = j1;
    }
    std::cout << std::setw(4) << payment_body << "\n";
    response_body = payment_body.get<test>();

    return true;
}

int main(int argc, char** argv) {
    std::string json_value = R"({
        "amount" : 1500,
        "value1" : "yes",
        "value2" : "no",
        "value3" : "maybe"
}
)";
    test resp{};
    check(resp, json_value);
    std::cout << resp.num << "\t" << resp.value_one << "\t "<<
        resp.value_two << "\t"<< resp.value_three << "\n"; 
    return 0;
}

The issue I am having is that my code needs the std::string types to be char * as this code is in a dll and the structure is passed from an application built with a different compiler. This structure is much larger in reality but I have seen potentially using something like this in from_json

std::string name = j.at("value1").get<std::string>();
p.value_one= new char[name.length() + 1];
std::strcpy(p.value_one, name.c_str());

Is their an alternative cleaner approach that could be taken here

[nlohmann]

The library stores std::string internally. You are right to use .c_str() to get a const char* and do with it what you like. To optimize, you could use references to avoid copying the std::string:

const std::string& name = j.at("value1").get<const std::string&>();