std::get(std::tuple)
Defined in header <tuple>
|
||
|
template
<
std::size_t I, class... Types
>
typename
std::tuple_element
<I, std::tuple
<Types...>>
::
type
&
|
(1) | (since C++11) (constexpr since C++14) |
|
template
<
std::size_t I, class... Types
>
typename
std::tuple_element
<I, std::tuple
<Types...>>
::
type
&&
|
(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
&
|
(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
&&
|
(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) |
[
0
,
sizeof...(Types)
)
T
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 (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. }
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 ((4) and (8)) |
See also
|
(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) |
|
(C++11)
|
creates a tuple of lvalue references or unpacks a tuple into individual objects (function template) |
| Structured binding (C++17) | binds the specified names to sub-objects or tuple elements of the initializer |