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;

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);}

Result

variant value: 12failed to get value!