std::get_if (std::variant)
Defined in header <variant>
.
Declarations
C++17
// 1)
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...>>>
get_if( const std::variant<Types...>* pv ) noexcept;
// 2)
template< class T, class... Types >
constexpr std::add_pointer_t<T> get_if( std::variant<Types...>* pv ) noexcept;
template< class T, class... Types >
constexpr std::add_pointer_t<const T> get_if( const std::variant<Types...>* pv ) noexcept;
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
#include <variant>
#include <iostream>
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);
}
variant value: 12
failed to get value!