std::tuple_element<std::tuple>

 

C++

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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)

 

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)

std::swap

get

Deduction guides(C++17)

Helper concepts

tuple-like (C++23)

Helper classes

tuple_size

tuple_element

uses_allocator

basic_common_reference (C++23)

common_type (C++23)

ignore

 

Defined in header <tuple>
template< std::size_t I, class... Types > struct tuple_element< I, std::tuple<Types...> >;		(since C++11)

Provides compile-time indexed access to the types of the elements of the tuple.

Member types

Member type	Definition
type	the type of Ith element of the tuple, where I is in [0, sizeof...(Types))

Possible implementation

template< std::size_t I, class T > struct tuple_element;   // recursive case template< std::size_t I, class Head, class... Tail > struct tuple_element<I, std::tuple<Head, Tail...>> : std::tuple_element<I-1, std::tuple<Tail...>> { };   // base case template< class Head, class... Tail > struct tuple_element<0, std::tuple<Head, Tail...>> { using type = Head; };

Example

Run this code

#include <iostream>
#include <string>
#include <tuple>
 
template <typename T> void printHelper() { std::cout << "unknown type\n"; }
template <> void printHelper<int>() { std::cout << "int\n"; }
template <> void printHelper<bool>() { std::cout << "bool\n"; }
template <> void printHelper<char>() { std::cout << "char\n"; }
template <> void printHelper<std::string>() { std::cout << "std::string\n"; }
 
template<std::size_t I, class T>
void printTypeAtIndex()
{
    std::cout << "index " << I << " has type: ";
    using SelectedType = std::tuple_element_t<I, T>;
    printHelper<SelectedType>();
}
 
int main()
{
    struct MyStruct {};
    using MyTuple = std::tuple<int, char, bool, std::string, MyStruct>;
    printTypeAtIndex<0, MyTuple>();
    printTypeAtIndex<1, MyTuple>();
    printTypeAtIndex<2, MyTuple>();
    printTypeAtIndex<3, MyTuple>();
    printTypeAtIndex<4, MyTuple>();
}

Output:

index 0 has type: int
index 1 has type: char
index 2 has type: bool
index 3 has type: std::string
index 4 has type: unknown type

See also

Structured binding (C++17)	binds the specified names to sub-objects or tuple elements of the initializer
tuple_element (C++11)	obtains the element types of a tuple-like type (class template)