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std::empty

From cppreference.com
< cpp‎ | iterator
 
C++
 
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empty
(C++17)
(C++17)
 
Defined in header <array>
Defined in header <deque>
Defined in header <flat_map>
Defined in header <flat_set>
Defined in header <forward_list>
Defined in header <inplace_vector>
Defined in header <iterator>
Defined in header <list>
Defined in header <map>
Defined in header <regex>
Defined in header <set>
Defined in header <span>
Defined in header <string>
Defined in header <string_view>
Defined in header <unordered_map>
Defined in header <unordered_set>
Defined in header <vector>
template< class C >
constexpr auto empty( const C& c ) -> 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)
template< class E >
constexpr bool empty( std::initializer_list<E> il ) noexcept;
 (3) (since C++17)

Returns whether the given range is empty.

1) Returns c.empty().
2) Returns false.
3) Returns il.size() == 0.

Contents

[edit] Parameters

c - a container or view with an empty member function
array - an array of arbitrary type
il - an std::initializer_list

[edit] Return value

1) c.empty()
2) false
3) il.size() == 0

[edit] Exceptions

1) May throw implementation-defined exceptions.

[edit] Notes

The overload for std::initializer_list is necessary because it does not have a member function empty.

Feature-test macro Value Std Feature
__cpp_lib_nonmember_container_access 201411L (C++17) std::size(), std::data(), and std::empty()

[edit] Possible implementation

First version 
template<class C>
[[nodiscard]] constexpr auto empty(const C& c) -> decltype(c.empty())
{
    return c.empty();
}