std::get_if (3) Linux Manual Page

std::get_if – std::get_if

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<(1)(since C++ 17)

                                 const std::variant_alternative_t<I, variant<Types...>>

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

template <class T, class... Types>

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

    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

// Run this code

#include <variant>

#include <iostream>
int main()

{
    std::variant<int, float> v{12};
    if (auto pval = std::get_if<int>(&v))
        std::cout << "variant value: " << *pval << '\n';
    else
        std::cout << "failed to get value!" << '\n';
}

Output:

  variant value: 12

See also

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