boost tuple

Posted 2022-01-26 sssblog

boost::tuple is a generalized version of std::pair. While std::pair can only store exactly two values, boost::tuple lets you choose how many values to store.

1. boost::tuple replacing std::pair

#include <boost/tuple/tuple.hpp>
#include <boost/tuple/tuple_io.hpp>
#include <iostream>
#include <string>

int main() 
  typedef boost::tuple<std::string, int> animal;
  typedef boost::tuple<std::string, int, bool> animal2;
  animal a("cat", 4);
  animal2 b("cat", 4, true);
  std::cout << a << std::endl;
  std::cout << std::boolalpha << b << std::endl;
  return 0;

输出为：

(cat 4)

(cat, 4, true)

2. creating tuples with boost::make_tuple()

#include <boost/tuple/tuple.hpp>
#include <boost/tuple/tuple_io.hpp>
#include <iostream>

int main() 
  std::cout.setf(std::ios::boolalpha);
  std::cout << boost::make_tuple("cat", 4, true) << std::endl;
  return 0;

boost::make_tuple() works like the helper function std::make_pair() for std::pair

3. reading and writing elements of a tuple

#include <boost/tuple/tuple.hpp>
#include <boost/tuple/tuple_io.hpp>
#include <string>
#include <iostream>

int main() 
  typedef boost::tuple<std::string, int, bool> animal;
  animal a = boost::make_tuple("cat", 4, true);
  std::cout << a.get<0>() << std::endl;
  std::cout << boost::get<0>(a) << std::endl;
  a.get<0>() = "dog";
  std::cout << std::boolalpha << a << std::endl;
  return 0;

输出为：

cat

cat

(dog 4 true)

There are two ways to access values in a tuple. You can call the member function get(), or you can pass the tuple to the free-standing function boost::get(). In both cases, the index of the corrsponding element in the tuple must be provided as a template parameter. The member function get() and the free-standing function boost::get() both return a reference that allows you to change a value inside a tuple.

4. creating a tier with boost::tie()

Boost.Tuple supports a specific form of tuples called tier. Tiers are tuples whose elements are all reference types. They can be constructed with the function boost::tie()

#include <boost/tuple/tuple.hpp>
#include <boost/tuple/tuple_io.hpp>
#include <string>
#include <iostream>

int main() 
  typedef boost::tuple<std::string&, int&, bool&> animal;
  std::string name = "cat";
  int legs = 4;
  bool tail = true;
  animal a = boost::tie(name, legs, tail);
  name = "dog";
  std::cout << std::boolalpha << a << std::endl;

  animal b = boost::make_tuple(boost::ref(name), boost::ref(legs), boost::ref(tail));
  name = "animal";
  std::cout << std::boolalpha << b << std::endl;
  return 0;

输出为：

(dog 4 true)

(animal 4 true)