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tuple_size class

  • Artikkeli

Reports the number of elements that a tuple contains.

Syntax

// TEMPLATE STRUCT tuple_size
template <class Tuple>
   struct tuple_size;

// number of elements in array
template <class Elem, size_t Size>
   struct tuple_size<array<Elem, Size>>
      : integral_constant<size_t, Size>;

// size of pair
template <class T1, class T2>
   struct tuple_size<pair<T1, T2>>
      : integral_constant<size_t, 2>

// size of tuple
template <class... Types>
   struct tuple_size<tuple<Types...>>
      : integral_constant<size_t, sizeof...(Types)>;

// size of const tuple
template <class Tuple>
   struct tuple_size<const Tuple>;

// size of volatile tuple
template <class Tuple>
   struct tuple_size<volatile Tuple>;

// size of const volatile tuple
template <class Tuple>
   struct tuple_size<const volatile Tuple>;

template <class T> inline constexpr size_t tuple_size_v = tuple_size<T>::value;

Parameters

Tuple
The type of the tuple.

Elem
The type of the array elements.

Size
The size of the array.

T1
The type of the first member of the pair.

T2
The type of the second member of the pair.

Types
The types of the tuple elements.

Remarks

The class template has a member value that is an integral constant expression whose value is the extent of the tuple type Tuple.

The template specialization for arrays has a member value that is an integral constant expression whose value is Size, which is the size of the array.

The template specialization for pair has a member value that is an integral constant expression whose value is 2.

Example

#include <tuple>
#include <iostream>

using namespace std;

typedef tuple<int, double, int, double> MyTuple;
int main()
{
    MyTuple c0(0, 1.5, 2, 3.7);

    // display contents "0 1 2 3"
    cout << get<0>(c0);
    cout << " " << get<1>(c0);
    cout << " " << get<2>(c0);
    cout << " " << get<3>(c0) << endl;

    // display size "4"
    cout << " " << tuple_size<MyTuple>::value << endl;
}

0 1.5 2 3.7
4

Requirements

Header: <tuple>

Header: <array> (for array specialization)

Header: <utility> (for pair specialization)

Namespace: std