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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