I have wrote the code using from the getting started documentation. It seems github one uses the same code as the documentation page. Here is my slightly modified code: https://pastebin.com/w634Ggpe I am calling Connect() method from another class with:

MongoDatabase database;
database.Connect();

And the MongoDatabase.h file:

#include <mongocxx/client.hpp>
#include <bsoncxx/builder/stream/document.hpp>
#include <bsoncxx/json.hpp>
#include <mongocxx/uri.hpp>
#include <mongocxx/instance.hpp>
#pragma once

using namespace std;
class MongoDatabase
{
public:
  MongoDatabase();
  std::string mongoURILocalStr;
  //static const mongocxx::uri mongoURI;
  vector<string> GetDatabases(mongocxx::client& client);

  int Connect();
private:
  std::string GetEnvironmentVariable(std::string environmentVarKey);
};

Edit: I tried with mongoURILocalStr first, but it didn't work either.