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std::holds_alternative

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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...

Contents

[edit] Parameters

v - variant to examine

[edit] Return value

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

[edit] 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';
}

Output:

variant holds int? false
variant holds string? true

[edit] See also

returns the zero-based index of the alternative held by the variant
(public member function) [edit]
reads the value of the variant given the index or the type (if the type is unique), throws on error
(function template) [edit]