std::make_optional

 

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std::optional

Member functions

optional::optional

optional::~optional

optional::operator=

Observers

optional::operator->optional::operator*

optional::operator booloptional::has_value

optional::value

optional::value_or

Iterators

optional::begin (C++26)

optional::end (C++26)

Monadic operations

optional::and_then (C++23)

optional::transform (C++23)

optional::or_else (C++23)

Modifiers

optional::emplace

optional::swap

optional::reset

Non-member functions

operator==operator!=operator<operator<=operator>operator>=operator<=> (C++20)

make_optional

swap(std::optional)

Deduction guides

Helper classes

hash<std::optional>

nullopt_t

in_place_t

bad_optional_access

Helper objects

nullopt

in_place

 

Defined in header <optional>
template< class T > constexpr std::optional<std::decay_t<T>> make_optional( T&& value );	(1)	(since C++17)
template< class T, class... Args > constexpr std::optional<T> make_optional( Args&&... args );	(2)	(since C++17)
template< class T, class U, class... Args > constexpr std::optional<T> make_optional( std::initializer_list<U> il,                                           Args&&... args );	(3)	(since C++17)

1) Creates an optional object from value. Effectively calls std::optional<std::decay_t<T>>(std::forward<T>(value)).

2) Creates an optional object constructed in-place from args.... Equivalent to return std::optional<T>(std::in_place, std::forward<Args>(args)...);.
This overload participates in overload resolution only if std::is_constructible_v<T, Args...> is true.

3) Creates an optional object constructed in-place from il and args.... Equivalent to return std::optional<T>(std::in_place, il, std::forward<Args>(args)...);.
This overload participates in overload resolution only if std::is_constructible_v<T, std::initializer_list<U>&, Args...> is true.

Parameters

value	-	the value to construct optional object with
il, args	-	arguments to be passed to the constructor of T

Return value

The constructed optional object.

Exceptions

Throws any exception thrown by the constructor of T.

Notes

T need not be movable for overloads (2,3) due to guaranteed copy elision.

Example

Run this code

#include <iomanip>
#include <iostream>
#include <optional>
#include <string>
#include <vector>
 
int main()
{
    auto op1 = std::make_optional<std::vector<char>>({'a','b','c'});
    std::cout << "op1: ";
    for (char c : op1.value())
        std::cout << c << ',';
    auto op2 = std::make_optional<std::vector<int>>(5, 2);
    std::cout << "\nop2: ";
    for (int i : *op2)
        std::cout << i << ',';
    std::string str{"hello world"};
    auto op3 = std::make_optional<std::string>(std::move(str));
    std::cout << "\nop3: " << std::quoted(op3.value_or("empty value")) << '\n';
    std::cout << "str: " << std::quoted(str) << '\n';
}

Possible output:

op1: a,b,c,
op2: 2,2,2,2,2,
op3: "hello world"
str: ""

See also

(constructor)

constructs the optional object (public member function)