Geolocation and Maps in C++: libcurl, nlohmann/json, Leaflet Libraries

Geolocation and Maps in C++: Tool Overview and Implementation Examples

In the modern world, geolocation data and interactive maps have become an integral part of many applications — from navigation services to games and monitoring systems. Development in C++ is no exception: although the language itself does not provide built-in tools for working with geodata, there is a powerful ecosystem of libraries that allows you to integrate geolocation and maps into your projects. In this article, we will look at key tools: libcurl for HTTP requests, nlohmann/json for parsing JSON API responses, and Leaflet (via HTML/JavaScript generation) for displaying maps.

1. Core Libraries for Working with Geolocation

libcurl is a powerful and time-tested library for transferring data over various protocols, including HTTP/HTTPS. It is ideal for sending requests to geolocation APIs (e.g., OpenStreetMap Nominatim or Google Maps Geocoding).

nlohmann/json is a modern, lightweight, and intuitive library for working with JSON. It allows you to easily serialize and deserialize data received from geolocation services.

Leaflet is the leading JavaScript library for creating interactive maps. In a C++ project, you can generate an HTML file that uses Leaflet to display data obtained by your C++ application.

2. Installing Required Components

To get started, you need to install the libraries. In most Linux distributions, this is done via the package manager:

# Installing libcurl and nlohmann-jsonsudo apt-get install libcurl4-openssl-dev nlohmann-json3-dev  # Debian/Ubuntusudo dnf install libcurl-devel json-devel                    # Fedora

To work with Leaflet, simply download the latest version and include the CSS/JS files in the generated HTML.

3. Example: Getting Coordinates by Address (Geocoding)

Let's implement a function that takes a city name and returns its latitude and longitude using the Nominatim API (OpenStreetMap).

#include <iostream>#include <string>#include <curl/curl.h>#include <nlohmann/json.hpp>

using json = nlohmann::json;

// Callback function for writing CURL response to a stringsize_t WriteCallback(void* contents, size_t size, size_t nmemb, std::string* output) {    size_t totalSize = size * nmemb;    output->append(static_cast<char*>(contents), totalSize);    return totalSize;}

std::pair<double, double> getCoordinates(const std::string& address) {    CURL* curl = curl_easy_init();    if (!curl) throw std::runtime_error("CURL initialization error");

    std::string response;    std::string url = "https://nominatim.openstreetmap.org/search?q="                       + curl_easy_escape(curl, address.c_str(), address.length())                       + "&format=json&limit=1";

    curl_easy_setopt(curl, CURLOPT_URL, url.c_str());    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteCallback);    curl_easy_setopt(curl, CURLOPT_WRITEDATA, &response);    curl_easy_setopt(curl, CURLOPT_USERAGENT, "CppGeoApp/1.0"); // Required for Nominatim

    CURLcode res = curl_easy_perform(curl);    curl_easy_cleanup(curl);

    if (res != CURLE_OK) throw std::runtime_error(curl_easy_strerror(res));

    json jsonData = json::parse(response);    if (jsonData.empty()) throw std::runtime_error("Address not found");

    double lat = jsonData[0]["lat"].get<double>();    double lon = jsonData[0]["lon"].get<double>();    return {lat, lon};}

int main() {    try {        auto [lat, lon] = getCoordinates("Moscow, Kremlin");        std::cout << "