std::get_if (std::variant)
From cppreference.com
| 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...>>> |
||
| template< std::size_t I, class... Types > constexpr std::add_pointer_t<const std::variant_alternative_t<I, std::variant<Types...>>> |
||
| (2) | (since C++17) | |
| template< class T, class... Types > constexpr std::add_pointer_t<T> |
||
| template< class T, class... Types > constexpr std::add_pointer_t<const T> |
||
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....Template parameters
| I | - | index to look up |
| Type | - | unique type to look up |
Parameters
| 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
| (C++17) |
reads the value of the variant given the index or the type (if the type is unique), throws on error (function template) |