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std::tuple

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

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
(public member function)
assigns the contents of one tuple to another
(public member function)
swaps the contents of two tuples
(public member function)

Non-member functions

creates a tuple object of the type defined by the argument types
(function template)
creates a tuple of lvalue references or unpacks a tuple into individual objects
(function template)
creates a tuple of rvalue references
(function template)
creates a tuple by concatenating any number of tuples
(function template)
tuple accesses specified element
(function template)
lexicographically compares the values in the tuple
(function template)
(C++11)
 specializes the std::swap algorithm
(function template)

Helper classes

obtains the size of tuple at compile time
(class template specialization)
obtains the type of the specified element
(class template specialization)
(C++11)
 specializes the std::uses_allocator type trait
(class template specialization)
placeholder to skip an element when unpacking a tuple using tie
(constant)

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

#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';
}

Output:

ID: 0, GPA: 3.8, grade: A, name: Lisa Simpson
ID: 1, GPA: 2.9, grade: C, name: Milhouse Van Houten

References

  • C++11 standard (ISO/IEC 14882:2011):
    • 20.4 Tuples [tuple]

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