std::tuple (3) - Linux Manuals

std::tuple: std::tuple

NAME

std::tuple - std::tuple

Synopsis

Defined in header <tuple>
template< class... Types > (since C++11)
class tuple;

Class template std::tuple is a fixed-size collection of heterogeneous values. It is a generalization of std::pair.

If (std::is_trivially_destructible_v<Types> && ...) is true, the destructor of tuple is trivial. (since C++17)

Template parameters

Types... - the types of the elements that the tuple stores. Empty list is supported.

Member functions

              constructs a new tuple
constructor (public member function)
              assigns the contents of one tuple to another
operator= (public member function)
              swaps the contents of two tuples
swap (public member function)

Non-member functions

                      creates a tuple object of the type defined by the argument types
make_tuple (function template)
                      creates a tuple of lvalue references or unpacks a tuple into individual objects
tie (function template)
                      creates a tuple of rvalue references
forward_as_tuple (function template)
                      creates a tuple by concatenating any number of tuples
tuple_cat (function template)
                      tuple accesses specified element
std::get(std::tuple) (function template)

operator==
operator!= lexicographically compares the values in the tuple
operator< (function template)
operator<=
operator>
operator>=

std::swap(std::tuple) specializes the std::swap algorithm
                      (function template)
(C++11)

Helper classes

                                obtains the size of tuple at compile time
tuple_size (class template specialization)
                                obtains the type of the specified element
tuple_element (class template specialization)

std::uses_allocator<std::tuple> specializes the std::uses_allocator type trait
                                (class template specialization)
(C++11)
                                placeholder to skip an element when unpacking a tuple using tie
ignore (constant)

Deduction_guides(since C++17)

Notes

Until C++17, a function could not return a tuple using list-initialization:

  std::tuple<int, int> foo_tuple()
  {
    return {1, -1}; // Error until C++17
    return std::make_tuple(1, -1); // Always works
  }

Example

// Run this code

  #include <tuple>
  #include <iostream>
  #include <string>
  #include <stdexcept>

  std::tuple<double, char, std::string> get_student(int id)
  {
      if (id == 0) return std::make_tuple(3.8, 'A', "Lisa Simpson");
      if (id == 1) return std::make_tuple(2.9, 'C', "Milhouse Van Houten");
      if (id == 2) return std::make_tuple(1.7, 'D', "Ralph Wiggum");
      throw std::invalid_argument("id");
  }

  int main()
  {
      auto student0 = get_student(0);
      std::cout << "ID: 0, "
                << "GPA: " << std::get<0>(student0) << ", "
                << "grade: " << std::get<1>(student0) << ", "
                << "name: " << std::get<2>(student0) << '\n';

      double gpa1;
      char grade1;
      std::string name1;
      std::tie(gpa1, grade1, name1) = get_student(1);
      std::cout << "ID: 1, "
                << "GPA: " << gpa1 << ", "
                << "grade: " << grade1 << ", "
                << "name: " << name1 << '\n';

      // C++17 structured binding:
      auto [ gpa2, grade2, name2 ] = get_student(2);
      std::cout << "ID: 2, "
                << "GPA: " << gpa2 << ", "
                << "grade: " << grade2 << ", "
                << "name: " << name2 << '\n';
  }

Output:

  ID: 0, GPA: 3.8, grade: A, name: Lisa Simpson
  ID: 1, GPA: 2.9, grade: C, name: Milhouse Van Houten
  ID: 2, GPA: 1.7, grade: D, name: Ralph Wiggum

References

* C++11 standard (ISO/IEC 14882:2011):

      * 20.4 Tuples [tuple]