std::holds_alternative (3) Linux Manual Page

std::holds_alternative – std::holds_alternative

Synopsis

Defined in header<variant>

    template <class T, class... Types>
    (since C++ 17)

        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

// Run this code

#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';
}

Output:

  variant holds int? false
  variant holds string? true

See also

                       returns the zero-based index of the alternative held by the variant
index (public member function)
std::get(std::variant) reads the value of the variant given the index or the type (if the type is unique), throws on error
                       (function template)
(C++17)