# std::initializer_list<T>::initializer_list

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< cpp‎ | utility‎ | initializer list

initializer_list() noexcept; |  | (since C++11) (until C++14)
constexpr initializer_list() noexcept; |  | (since C++14)

Constructs an empty initializer list.

### Parameters

(none)

### Complexity

Constant

### Notes

Despite a lack of constructors, it is possible to create non-empty initializer lists. Instances of `std::initializer_list` are implicitly constructed when:

- a braced-init-list is used in list-initialization, including function-call list initialization and assignment expressions (not to be confused with constructor initializer lists)
- a braced-init-list is bound to auto, including in a ranged for loop

### Example

Run this code

    #include <iostream>
    #include <initializer_list>

    int main()
    {
        std::initializer_list<int> empty_list;
        std::cout << "empty_list.size(): " << empty_list.size() << '\n';

        // create initializer lists using list-initialization
        std::initializer_list<int> digits {1, 2, 3, 4, 5};
        std::cout << "digits.size(): " << digits.size() << '\n';

        // special rule for auto means 'fractions' has the
        // type std::initializer_list<double>
        auto fractions = {3.14159, 2.71828};
        std::cout << "fractions.size(): " << fractions.size() << '\n';

        // create constexpr initializer list (since C++14)
        static constexpr auto ab = {'a', 'b'};
        static_assert(ab.size() == 2 and *ab.begin() == 'a');
    }

Output:

    empty_list.size(): 0
    digits.size(): 5
    fractions.size(): 2

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