std::tuple

 

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Language support Type support (basic types, RTTI) Library feature-test macros (C++20) Dynamic memory management Program utilities Coroutine support (C++20) Variadic functions is_constant_evaluated (C++20) is_within_lifetime (C++26) initializer_list (C++11) source_location (C++20) Three-way comparison three_way_comparablethree_way_comparable_with (C++20)(C++20) strong_ordering (C++20) weak_ordering (C++20) partial_ordering (C++20) common_comparison_category (C++20) compare_three_way_result (C++20) compare_three_way (C++20) strong_order (C++20) weak_order (C++20) partial_order (C++20) compare_strong_order_fallback (C++20) compare_weak_order_fallback (C++20) compare_partial_order_fallback (C++20)   is_eqis_ltis_lteq (C++20)(C++20)(C++20)   is_neqis_gtis_gteq (C++20)(C++20)(C++20)

General utilities Date and time Function objects Formatting library (C++20)   bitset hash (C++11) Relational operators (deprecated in C++20) rel_ops::operator!=rel_ops::operator>    rel_ops::operator<=rel_ops::operator>= Integer comparison functions cmp_equalcmp_lesscmp_less_than (C++20)(C++20)(C++20)   cmp_not_equalcmp_greatercmp_greater_than (C++20)(C++20)(C++20) in_range (C++20) Swap and type operations swap ranges::swap (C++20) exchange (C++14) declval (C++11) to_underlying (C++23) forward (C++11) forward_like (C++23) move (C++11) move_if_noexcept (C++11) as_const (C++17) Common vocabulary types pair tuple (C++11) optional (C++17) any (C++17) variant (C++17) tuple_size (C++11) tuple_element (C++11) apply (C++17) make_from_tuple (C++17) expected (C++23) Elementary string conversions to_chars (C++17) from_chars (C++17) chars_format (C++17) to_chars_result (C++17) from_chars_result (C++17)

 

std::tuple

Member functions

tuple::tuple

tuple::operator=

tuple::swap

Non-member functions

make_tuple

tie

forward_as_tuple

tuple_cat

operator==operator!=operator<operator<=operator>operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)

swap(std::tuple)

get(std::tuple)

Helper concepts

tuple-like (C++23)

Helper classes

tuple_size<std::tuple>

tuple_element<std::tuple>

uses_allocator<std::tuple>

basic_common_reference<std::tuple> (C++23)

common_type<std::tuple> (C++23)

formatter<std::tuple> (C++23)

ignore

Deduction guides(C++17)

 

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<Ti>::value is true for every Ti in Types, the destructor of std::tuple is trivial.

If a program declares an explicit or partial specialization of std::tuple, the program is ill-formed, no diagnostic required.

Template parameters

Types...

-

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

Member functions

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

Non-member functions

make_tuple (C++11)	creates a tuple object of the type defined by the argument types (function template)
tie (C++11)	creates a tuple of lvalue references or unpacks a tuple into individual objects (function template)
forward_as_tuple (C++11)	creates a tuple of forwarding references (function template)
tuple_cat (C++11)	creates a tuple by concatenating any number of tuples (function template)
get(std::tuple) (C++11)	tuple accesses specified element (function template)
operator==operator!=operator<operator<=operator>operator>=operator<=> (removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(C++20)	lexicographically compares the values in the tuple (function template)
std::swap(std::tuple) (C++11)	specializes the std::swap algorithm (function template)

Helper concepts

tuple-likepair-like (C++23)

specifies that a type implemented the tuple protocol (std::get, std::tuple_element, std::tuple_size) (exposition-only concept*)

Helper classes

std::tuple_size<std::tuple> (C++11)	obtains the size of a tuple (class template specialization)
std::tuple_element<std::tuple> (C++11)	obtains the type of the specified element (class template specialization)
std::uses_allocator<std::tuple> (C++11)	specializes the std::uses_allocator type trait (class template specialization)
std::basic_common_reference<tuple-like> (C++23)	determines the common reference type of a tuple and a tuple-like type (class template specialization)
std::common_type<tuple-like> (C++23)	determines the common type of a tuple and a tuple-like type (class template specialization)
std::formatter<std::tuple> (C++23)	formatting support for tuple (class template specialization)
ignore (C++11)	placeholder to skip an element when unpacking a tuple using tie (constant)

Helper specializations

template< class... Ts > constexpr bool enable_nonlocking_formatter_optimization<std::tuple<Ts...>>  = (enable_nonlocking_formatter_optimization<Ts> && ...);		(since C++23)

This specialization of std::enable_nonlocking_formatter_optimization enables efficient implementation of std::print and std::println for printing a tuple object when each element type enables it.

Notes

Since the "shape" of a tuple – its size, the types of its elements, and the ordering of those types – are part of its type signature, they must all be available at compile time and can only depend on other compile-time information. This means that many conditional operations on tuples – in particular, conditional prepend/append and filter – are only possible if the conditions can be evaluated at compile time. For example, given a std::tuple<int, double, int>, it is possible to filter on types – e.g. returning a std::tuple<int, int> – but not to filter on whether or not each element is positive (which would have a different type signature depending on runtime values of the tuple), unless all the elements were themselves constexpr.

As a workaround, one can work with tuples of std::optional, but there is still no way to adjust the size based on runtime information.

Until N4387 (applied as a defect report for C++11), a function could not return a tuple using copy-list-initialization:

std::tuple<int, int> foo_tuple()
{
    return {1, -1};  // Error until N4387
    return std::tuple<int, int>{1, -1}; // Always works
    return std::make_tuple(1, -1); // Always works
}

Example

Run this code

#include <iostream>
#include <stdexcept>
#include <string>
#include <tuple>
 
std::tuple<double, char, std::string> get_student(int id)
{
    switch (id)
    {
        case 0: return {3.8, 'A', "Lisa Simpson"};
        case 1: return {2.9, 'C', "Milhouse Van Houten"};
        case 2: return {1.7, 'D', "Ralph Wiggum"};
        case 3: return {0.6, 'F', "Bart Simpson"};
    }
 
    throw std::invalid_argument("id");
}
 
int main()
{
    const 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';
 
    const auto student1 = get_student(1);
    std::cout << "ID: 1, "
              << "GPA: " << std::get<double>(student1) << ", "
              << "grade: " << std::get<char>(student1) << ", "
              << "name: " << std::get<std::string>(student1) << '\n';
 
    double gpa2;
    char grade2;
    std::string name2;
    std::tie(gpa2, grade2, name2) = get_student(2);
    std::cout << "ID: 2, "
              << "GPA: " << gpa2 << ", "
              << "grade: " << grade2 << ", "
              << "name: " << name2 << '\n';
 
    // C++17 structured binding:
    const auto [gpa3, grade3, name3] = get_student(3);
    std::cout << "ID: 3, "
              << "GPA: " << gpa3 << ", "
              << "grade: " << grade3 << ", "
              << "name: " << name3 << '\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
ID: 3, GPA: 0.6, grade: F, name: Bart Simpson

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 2796	C++11	triviality of the destructor of std::tuple was unspecified	specified
LWG 3990	C++11	a program could declare an explicit or partial specialization of std::tuple	the program is ill-formed in this case (no diagnostic required)

References

• C++23 standard (ISO/IEC 14882:2024):

• 22.4 Tuples [tuple]

• C++20 standard (ISO/IEC 14882:2020):

• 20.5 Tuples [tuple]

• C++17 standard (ISO/IEC 14882:2017):

• 23.5 Tuples [tuple]

• C++14 standard (ISO/IEC 14882:2014):

• 20.4 Tuples [tuple]

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

• 20.4 Tuples [tuple]

See also

pair	implements binary tuple, i.e. a pair of values (class template)