std::initializer_list<T>::initializer_list
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std::initializer_list
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initializer_list::initializer_list
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initializer_list() noexcept;
(since C++11) (constexpr since C++14)
Constructs an empty initializer list.
Contents
[edit] Parameters
(none)
[edit] Complexity
Constant
[edit] 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
[edit] Example
Run this code
#include <initializer_list> #include <iostream> 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