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std::empty - cppreference.com

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Defined in header <array>

Defined in header <deque>

Defined in header <flat_map>

(since C++23)

Defined in header <flat_set>

(since C++23)

Defined in header <forward_list>

Defined in header <inplace_vector>

(since C++26)

Defined in header <iterator>

Defined in header <list>

Defined in header <map>

Defined in header <optional>

(since C++26)

Defined in header <regex>

Defined in header <set>

Defined in header <span>

(since C++20)

Defined in header <stacktrace>

(since C++23)

Defined in header <string>

Defined in header <string_view>

Defined in header <unordered_map>

Defined in header <unordered_set>

Defined in header <valarray>

Defined in header <vector> 

template< class C >
constexpr auto empty( const C& c ) noexcept(noexcept(c.empty()))
    -> decltype(c.empty());
(1) (since C++17) 
template< class T, std::size_t N >
constexpr bool empty( const T (&array)[N] ) noexcept;
(2) (since C++17)

Returns whether the given range is empty.

1) Returns c.empty().

2) Returns false.

Parameters

c - a container or view with an empty member function
array - an array of arbitrary type

Return value

1) c.empty()

2) false

Exceptions

1) What and when the underlying c.empty() call throws.

Notes

Feature-test macro Value Std Feature
__cpp_lib_nonmember_container_access 201411L (C++17) std::size(), std::data(), and std::empty()
__cpp_lib_initializer_list 202511L (C++26)
(DR11)		 data and empty member functions of std::initializer_list;
removing unnecessary free functions for std::initializer_list[1]
  1. ↑ As of 2026-05-27, libstdc++ has not treated the addition and removal of functions from P3016R6 as a defect report against C++11, and only applies the changes since C++26.
    The overload for std::initializer_list was necessary before P3016R6 because it did not have a member function empty.

Possible implementation

First version 
template<class C>
[[nodiscard]] constexpr auto empty(const C& c) noexcept(noexcept(c.empty()))
    -> decltype(c.empty())
{
    return c.empty();
}
Second version 
template<class T, std::size_t N>
[[nodiscard]] constexpr bool empty(const T (&array)[N]) noexcept
{
    return false;
}

Example

#include <iostream>
#include <vector>

template<class T>
void print(const T& container)
{
    if (std::empty(container))
        std::cout << "Empty\n";
    else
    {
        std::cout << "Elements:";
        for (const auto& element : container)
            std::cout << ' ' << element;
        std::cout << '\n';
    }
}

int main()
{
    std::vector<int> c = {1, 2, 3};
    print(c);
    c.clear();
    print(c);
    
    int array[] = {4, 5, 6};
    print(array);
    
    auto il = {7, 8, 9};
    print(il);
}

Output: 

Elements: 1 2 3
Empty
Elements: 4 5 6
Elements: 7 8 9

Defect report

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
P3016R6 C++17 1) non-member std::empty overload was provided for std::initializer_list
2) std::empty was not required to propagate exception specification 		1) removed
2) required

See also