NAME

std::holds_alternative - std::holds_alternative

Synopsis

Defined in header <variant>
template< class T, class... Types >
constexpr bool holds_alternative( const std::variant<Types...>& v ) (since C++17)
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
index variant
(public member function)
std::get(std::variant) reads the value of the variant given the index or the type
(C++17) (if the type is unique), throws on error
(function template)