NAME¶

std::get_if(std::variant) - std::get_if(std::variant)

Synopsis¶

Defined in header <variant>
template< std::size_t I, class... Types >

constexpr std::add_pointer_t<std::variant_alternative_t<I,
std::variant<Types...>>>

get_if( std::variant<Types...>* pv ) noexcept;
template< std::size_t I, class... Types >

constexpr std::add_pointer_t<const
std::variant_alternative_t<I, std::variant<Types...>>>
(1) (since
get_if( const std::variant<Types...>* pv ) noexcept; C++17)
template< class T, class... Types >

constexpr std::add_pointer_t<T>

get_if( std::variant<Types...>* pv ) noexcept; (2) (since
template< class T, class... Types > C++17)

constexpr std::add_pointer_t<const T>

get_if( const std::variant<Types...>* pv ) noexcept;

1) Index-based non-throwing accessor: If pv is not a null pointer and pv->index() ==
I, returns a pointer to the value stored in the variant pointed to by pv. Otherwise,
returns a null pointer value. The call is ill-formed if I is not a valid index in
the variant.
2) Type-based non-throwing accessor: Equivalent to (1) with I being the zero-based
index of T in Types.... The call is ill-formed if T is not a unique element of
Types....

Parameters¶

I - index to look up
Type - unique type to look up
pv - pointer to a variant

Return value¶

Pointer to the value stored in the pointed-to variant or null pointer on error.

Example¶

// Run this code

#include <iostream>
#include <variant>

int main()
{
auto check_value = [](const std::variant<int, float>& v)
{
if (const int* pval = std::get_if<int>(&v))
std::cout << "variant value: " << *pval << '\n';
else
std::cout << "failed to get value!" << '\n';
};

std::variant<int, float> v{12}, w{3.f};
check_value(v);
check_value(w);
}

Output:¶

variant value: 12
failed to get value!

See also¶

get(std::variant) reads the value of the variant given the index or the type (if the
(C++17) type is unique), throws on error
(function template)

Category:¶

* Uses of dcl rev begin with nonempty note