table of contents
std::any::has_value(3) | C++ Standard Libary | std::any::has_value(3) |
NAME¶
std::any::has_value - std::any::has_value
Synopsis¶
bool has_value() const noexcept; (since C++17)
Checks whether the object contains a value.
Parameters¶
(none)
Return value¶
true if instance contains a value, otherwise false.
Example¶
// Run this code
#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
See also¶
reset destroys contained object
(public member function)
2022.07.31 | http://cppreference.com |