std::holds_alternative

Defined in header <variant>.

Declarations

Since C++17

template< class T, class... Types >
constexpr bool holds_alternative( const std::variant<Types...>& v ) noexcept;

Checks if the variant v holds the alternative T. The call is ill-formed if T does not appear exactly once in Types...

Parameters

v - variant to examine

Return value

true if the variant currently holds the alternative T, false otherwise.

Example

#include <variant>
#include <string>
#include <iostream>
int main()
{
    std::variant<int, std::string> v = "abc";
    std::cout << std::boolalpha
              << "variant holds int? "
              << std::holds_alternative<int>(v) << '\n'
              << "variant holds string? "
              << std::holds_alternative<std::string>(v) << '\n';
}

Result

variant holds int? false
variant holds string? true