boost variant

Boost Variant resembles union. You can store values of different types in a boost::variant.

1.

#include <boost/variant.hpp>
#include <string>

int main() {
  boost::variant<double, char, std::string> v;
  v = 3.14;
  v = 'A';
  v = "Boost";
}

boost::variant is a template, at least one parameter must be specified. One or more template parameters specify the supported types.

2. accessing values in boost::variant with boost::get()

#include <boost/variant.hpp>
#include <string>
#include <iostream>

int main() {
  boost::variant<double, char, std::string> v;
  v = 3.14;
  std::cout << boost::get<double>(v) << std::endl;
  v = 'A';
  std::cout << boost::get<char>(v) << std::endl;
  v = "Boost";
  std::cout << boost::get<std::string>(v) << std::endl;
  return 0;
}

to display the stored values of v, use the free-standing function boost::get().

3. using a visitor for boost::variant