std::holds_alternative

 

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std::variant

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Defined in header <variant>
template< class T, class... Types > constexpr bool holds_alternative( const std::variant<Types...>& v ) noexcept;		(since C++17)

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

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