std:: get (std::tuple)

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C++
Utilities library
General utilities
Relational operators (deprecated in C++20)
std::tuple
Defined in header <tuple>
template < std:: size_t I, class ... Types >

typename std:: tuple_element < I, std:: tuple < Types... >> :: type &

get ( std:: tuple < Types... > & t ) noexcept ;
(1) (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 ;
(2) (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 ;
(3) (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 ;
(4) (since C++11)
(constexpr since C++14)
template < class T, class ... Types >
constexpr T & get ( std:: tuple < Types... > & t ) noexcept ;
(5) (since C++14)
template < class T, class ... Types >
constexpr T && get ( std:: tuple < Types... > && t ) noexcept ;
(6) (since C++14)
template < class T, class ... Types >
constexpr const T & get ( const std:: tuple < Types... > & t ) noexcept ;
(7) (since C++14)
template < class T, class ... Types >
constexpr const T && get ( const std:: tuple < Types... > && t ) noexcept ;
(8) (since C++14)
1-4) Extracts the I th element from the tuple. I must be an integer value in [ ​ 0 ​ , sizeof... ( Types ) ) .
5-8) Extracts the element of the tuple t whose type is T . Fails to compile unless the tuple has exactly one element of that type.

Parameters

t - tuple whose contents to extract

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

Example

Run this code 
#include <iostream>
#include <string>
#include <tuple>
 
int main()
{
    auto t = std::make_tuple(1, "Foo", 3.14);
 
    // Note: std::get generates an incorrect link to std::get<std::variant>
    using std::get;
 
    // Index-based access
    std::cout << "( " << get<0>(t)
              << ", " << get<1>(t)
              << ", " << get<2>(t)
              << " )\n";
 
    // Type-based access (C++14 or later)
    std::cout << "( " << get<int>(t)
              << ", " << get<const char*>(t)
              << ", " << get<double>(t)
              << " )\n";
 
    // Note: std::tie and structured binding may also be used to decompose a tuple.
}

Output: 

( 1, Foo, 3.14 )
( 1, Foo, 3.14 )

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 2485 C++11 (by index)
C++14 (by type) 		there are no overloads for const tuple && added these overloads

See also

Structured binding (C++17) binds the specified names to sub-objects or tuple elements of the initializer
(C++11)
accesses an element of an array
(function template)
(C++11)
accesses an element of a pair
(function template)
(C++17)
reads the value of the variant given the index or the type (if the type is unique), throws on error
(function template)
(C++20)
obtains iterator or sentinel from a std::ranges::subrange
(function template)
(C++26)
obtains a reference to real or imaginary part from a std::complex
(function template)
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