std::get(std::tuple)

Since C++14

Header: <tuple>

1-4) Extracts the Ith element from the tuple. I must be an integer value in [0,sizeof…(Types)).

# Declarations

template< std::size_t I, class... Types >
typename std::tuple_element<I, std::tuple<Types...>>::type&
get( std::tuple<Types...>& t ) noexcept;

(since C++11) (constexpr since C++14)

template< std::size_t I, class... Types >
typename std::tuple_element<I, std::tuple<Types...>>::type&&
get( std::tuple<Types...>&& t ) noexcept;

(since C++11) (constexpr since C++14)

template< std::size_t I, class... Types >
const typename std::tuple_element<I, std::tuple<Types...>>::type&
get( const std::tuple<Types...>& t ) noexcept;

(since C++11) (constexpr since C++14)

template< std::size_t I, class... Types >
const typename std::tuple_element<I, std::tuple<Types...>>::type&&
get( const std::tuple<Types...>&& t ) noexcept;

(since C++11) (constexpr since C++14)

template< class T, class... Types >
constexpr T& get( std::tuple<Types...>& t ) noexcept;

(since C++14)

template< class T, class... Types >
constexpr T&& get( std::tuple<Types...>&& t ) noexcept;

(since C++14)

template< class T, class... Types >
constexpr const T& get( const std::tuple<Types...>& t ) noexcept;

(since C++14)

template< class T, class... Types >
constexpr const T&& get( const std::tuple<Types...>&& t ) noexcept;

(since C++14)

# Parameters

# Return value

A reference to the selected element of t.

# Notes

Feature-test macro Value Std Feature __cpp_lib_tuples_by_type 201304L (C++14) Addressing tuples by type (5-8)

# Example

#include <cassert>
#include <iostream>
#include <string>
#include <tuple>
 
int main()
{
    auto x = std::make_tuple(1, "Foo", 3.14);
 
    // Index-based access
    std::cout << "( " << std::get<0>(x)
              << ", " << std::get<1>(x)
              << ", " << std::get<2>(x)
              << " )\n";
 
    // Type-based access (since C++14)
    std::cout << "( " << std::get<int>(x)
              << ", " << std::get<const char*>(x)
              << ", " << std::get<double>(x)
              << " )\n";
 
    const std::tuple<int, const int, double, double> y(1, 2, 6.9, 9.6);
    const int& i1 = std::get<int>(y); // OK: not ambiguous
    assert(i1 == 1);
    const int& i2 = std::get<const int>(y); // OK: not ambiguous
    assert(i2 == 2);
    // const double& d = std::get<double>(y); // Error: ill-formed (ambiguous)
 
    // Note: std::tie and structured binding can be
    // used to unpack a tuple into individual objects.
}

# Defect reports

DRApplied toBehavior as publishedCorrect behavior
LWG 2485C++11 (by index)C++14 (by type)there are no overloads for const tuple&&added these overloads ((4) and (8))

# See also