JSON_Spirit: how to get value

I am working with cpp to build a project.

My project needs a file to do some configuration and I decided to use a file with JSON format. Here is an example:

{
    "agentname":"agent1",
    "server":[
        {"ip":"192.168.0.1"},
        {"port":"9999"}
    ]    
}

Now I need to read this file so I use the JSON_Spirit. Here is my code:

ifstream conf("config", ios::in);
json_spirit::mValue mvalue;
json_spirit::read(conf, mvalue);
json_spirit::mObject obj = mvalue.get_obj();
string agentname = obj.find("agentname")->second.get_str();

After the code, I can get agentname.
But I don't know how to get ip and port.
I have tried like this:

string ip = obj.find("server")->second.find("ip")->second.get_str();

I think it should be something like this but the code above doesn't work.

I find that with json_spirit it helps to have a few utility accessor functions. Also, take care to examine the actual contents of the document:

This will work:

#include <json_spirit.h>
#include <iostream>
#include <sstream>

using namespace std;

const string test_str =
R"json({
    "agentname":"agent1",
    "server":[
          {"ip":"192.168.0.1"},
          {"port":"9999"}
    ]
}
)json";

json_spirit::mValue read_document(std::istream& is) {
    json_spirit::mValue result;
    auto ok = json_spirit::read(is, result);
    if (!ok) {
        throw std::runtime_error { "invalid json" };
    }
    return result;
}

const json_spirit::mValue& get_object_item(const json_spirit::mValue& element, const std::string& name)
{
    return element.get_obj().at(name);
}

const json_spirit::mValue& get_array_item(const json_spirit::mValue& element, size_t index)
{
    return element.get_array().at(index);
}

int main()
{
    istringstream conf(test_str);

    auto doc = read_document(conf);

    const auto& agentname = get_object_item(doc, "agentname");
    const auto& server = get_object_item(doc, "server");
    const auto& ip_holder = get_array_item(server, 0);
    const auto& ip = get_object_item(ip_holder, "ip");
    const auto& port = get_object_item(get_array_item(server, 1), "port");

    cout << agentname.get_str() << endl
    << ip.get_str() << endl
    << port.get_str() << endl;

    return 0;
}

expected output:

agent1
192.168.0.1
9999