std::initializer_list<T>::initializer_list

 

C++

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Utilities library

Language support Type support (basic types, RTTI) Library feature-test macros (C++20) Dynamic memory management Program utilities Coroutine support (C++20) Variadic functions is_constant_evaluated (C++20) is_within_lifetime (C++26) initializer_list (C++11) source_location (C++20) Three-way comparison (C++20) three_way_comparablethree_way_comparable_with (C++20)(C++20) strong_ordering (C++20) weak_ordering (C++20) partial_ordering (C++20) common_comparison_category (C++20) compare_three_way_result (C++20) compare_three_way (C++20) strong_order (C++20) weak_order (C++20) partial_order (C++20) compare_strong_order_fallback (C++20) compare_weak_order_fallback (C++20) compare_partial_order_fallback (C++20)    is_eqis_neqis_ltis_lteqis_gtis_gteq (C++20)(C++20)(C++20)(C++20)(C++20)(C++20)

General utilities Date and time Function objects Formatting library (C++20) bitset hash (C++11) Relational operators (deprecated in C++20) rel_ops::operator!=rel_ops::operator> rel_ops::operator<=rel_ops::operator>= Integer comparison functions cmp_equalcmp_lesscmp_less_than (C++20)(C++20)(C++20)    cmp_not_equalcmp_greatercmp_greater_than (C++20)(C++20)(C++20) in_range (C++20) Swap and type operations swap ranges::swap (C++20) exchange (C++14) declval (C++11) to_underlying (C++23) forward (C++11) forward_like (C++23) move (C++11) move_if_noexcept (C++11) as_const (C++17) Common vocabulary types pair tuple (C++11) optional (C++17) any (C++17) variant (C++17) tuple_size (C++11) tuple_element (C++11) apply (C++17) make_from_tuple (C++17) expected (C++23) Elementary string conversions to_chars (C++17) from_chars (C++17) chars_format (C++17)

 

std::initializer_list

Member functions

initializer_list::initializer_list

Capacity

initializer_list::size

Iterators

initializer_list::begin

initializer_list::end

Non-member functions

std::begin

std::end

 

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