std::initializer_list<T>::initializer_list

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Diagnostics library

Memory management library

Metaprogramming library (C++11)

General utilities library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Strings library

Text processing library

Numerics library

Date and time library

Input/output library

Filesystem library (C++17)

Concurrency support library (C++11)

Execution control library (C++26)

Technical specifications

Symbols index

External libraries

 

Utilities library

Language support Type support (basic types, RTTI) Library feature-test macros (C++20) Program utilities Variadic functions initializer_list (C++11) is_constant_evaluated (C++20) is_within_lifetime (C++26) source_location (C++20) Coroutine support (C++20) Contract support (C++26) Three-way comparison 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_ltis_lteq (C++20)(C++20)(C++20)   is_neqis_gtis_gteq (C++20)(C++20)(C++20)

General utilities Function objects Bit manipulation (C++20) C-style bit manipulation (C++26) 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)

 

std::initializer_list

Member functions

initializer_list::initializer_list

Capacity

initializer_list::size

Iterators

initializer_list::begin

initializer_list::end

Non-member functions

begin(std::initializer_list)

end(std::initializer_list)

 

initializer_list() noexcept;		(since C++11) (constexpr 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 <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

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