std:: empty

Returns whether the given range is empty.

Parameters

Return value

Exceptions

Notes

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

Possible implementation

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

template<class T, std::size_t N>
[[nodiscard]] constexpr bool empty(const T (&array)[N]) noexcept
{
    return false;
}

template<class E>
[[nodiscard]] constexpr bool empty(std::initializer_list<E> il) noexcept
{
    return il.size() == 0;
}

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);
}

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

See also