std::holds_alternative

 

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std::variant

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variant::visit (C++26)

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visit(std::variant)

holds_alternative

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swap(std::variant)

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monostate

bad_variant_access

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variant_alternative

hash<std::variant>

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variant_npos

 

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 <cassert>
#include <string>
#include <variant>

int main()
{
    std::variant<int, std::string> v = "abc";
    assert(not std::holds_alternative<int>(v));
    assert(std::holds_alternative<std::string>(v));
}

See also

index	returns the zero-based index of the alternative held by the variant (public member function)
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)