std::make_optional
cppreference.com
<tbody>
</tbody>
template< class T > constexpr std::optional<std::decay_t<T>> make_optional( T&& value ); |
(1) | ( C++17) |
template< class T, class... Args > constexpr std::optional<T> make_optional( Args&&... args ); |
(2) | ( C++17) |
template< class T, class U, class... Args > constexpr std::optional<T> make_optional( std::initializer_list<U> il, Args&&... args ); |
(3) | ( C++17) |
1) optional
value. std::optional<std::decay_t<T>>(std::forward<T>(value)).2) optional,
args.... return std::optional<T>(std::in_place, std::forward<Args>(args)...);.3) optional,
il args.... return std::optional<T>(std::in_place, il, std::forward<Args>(args)...);.| value | optional | |
| il, args | T.
|
optional.
, T.
T (2-3) - .
#include <optional>
#include <iostream>
#include <iomanip>
#include <vector>
#include <string>
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{" "};
auto op3 = std::make_optional<std::string>(std::move(str));
std::cout << "\nop3: " << std::quoted(op3.value_or(" ")) << '\n';
std::cout << "str: " << std::quoted(str) << '\n';
}
:
op1: a,b,c,
op2: 2,2,2,2,2,
op3: " "
str: ""
| (public -) |