sizeof... operator

C++

Language

Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

C++ language

Templates

parameters and arguments

class templates

function templates

class member templates

variable templates(C++14)

template argument deduction

class template argument deduction(C++17)

explicit (full) specialization

partial specialization

dependent names

parameter packs(C++11)

sizeof... (C++11)

fold-expressions(C++17)

SFINAE

Constraints and concepts(C++20)

Queries the number of elements in a parameter pack.

Syntax

sizeof...( parameter_pack )		(since C++11)

Returns a constant of type std::size_t.

Explanation

Returns the number of elements in a parameter pack.

Keywords

sizeof

Example

Run this code

#include <iostream>
#include <array>
#include <type_traits>

template<typename... Ts>
constexpr auto make_array(Ts&&... ts)
    -> std::array<std::common_type_t<Ts...>,sizeof...(ts)>
{
    return { std::forward<Ts>(ts)... };
}

int main()
{
    auto b = make_array(1, 2, 3);
    std::cout << b.size() << '\n';
    for (auto i : b)
        std::cout << i << ' ';
}

Output:

3
1 2 3

See also

• sizeof