bool has_value() const noexcept; | (since C++17) |
Checks whether the object contains a value.
(none).
true if instance contains a value, otherwise false.
#include <any>
#include <iostream>
#include <string>
int main()
{
std::boolalpha(std::cout);
std::any a0;
std::cout << "a0.has_value(): " << a0.has_value() << '\n';
std::any a1 = 42;
std::cout << "a1.has_value(): " << a1.has_value() << '\n';
std::cout << "a1 = " << std::any_cast<int>(a1) << '\n';
a1.reset();
std::cout << "a1.has_value(): " << a1.has_value() << '\n';
auto a2 = std::make_any<std::string>("Milky Way");
std::cout << "a2.has_value(): " << a2.has_value() << '\n';
std::cout << "a2 = \"" << std::any_cast<std::string&>(a2) << "\"\n";
a2.reset();
std::cout << "a2.has_value(): " << a2.has_value() << '\n';
}Output:
a0.has_value(): false a1.has_value(): true a1 = 42 a1.has_value(): false a2.has_value(): true a2 = "Milky Way" a2.has_value(): false
| destroys contained object (public member function) |
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