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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

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