如何使用mongo cxx驱动程序检索特定字段的值

#include <mongocxx/client.hpp>
#include <mongocxx/instance.hpp>
#include <bsoncxx/json.hpp>

int main() {
    // 初始化mongo cxx驱动程序
    mongocxx::instance inst{};

    // 建立与MongoDB数据库的连接
    mongocxx::client conn{mongocxx::uri{"mongodb://localhost:27017"}};

    // 选择数据库和集合
    mongocxx::database db = conn["mydatabase"];
    mongocxx::collection coll = db["mycollection"];

    // 构建查询条件
    bsoncxx::builder::stream::document filter_builder{};
    filter_builder << "field_name" << "desired_value";

    // 执行查询操作
    mongocxx::cursor cursor = coll.find(filter_builder.view());

    // 处理查询结果
    for (auto&& doc : cursor) {
        bsoncxx::document::element element = doc["field_name"];
        if (element) {
            std::cout << bsoncxx::to_json(element.get_value()) << std::endl;
        }
    }

    return 0;
}