std::get_if (std::variant)
Defined in header <variant> |
||
---|---|---|
(1) | (since C++17) | |
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) | (since C++17) | |
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; |
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
#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); }
Output:
variant value: 12 failed to get value!
See also
(C++17)
|
reads the value of the variant given the index or the type (if the type is unique), throws on error (function template) |
© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/w/cpp/utility/variant/get_if