std::get(std::variant) (3) Linux Manual Page

std::get(std::variant) – std::get(std::variant)

Synopsis

Defined in header<variant>

    template <std::size_t I, class... Types>

    constexpr std::variant_alternative_t<

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

        > &
    get(std::variant<Types...> &v);

template <std::size_t I, class... Types>

constexpr std::variant_alternative_t<

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

    > &&
get(std::variant<Types...> &&v);

template <std::size_t I, class... Types>

constexpr std::variant_alternative_t<

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

    > const &
get(const std::variant<Types...> &v);
(1)(since C++ 17)

    template <std::size_t I, class... Types>

    constexpr std::variant_alternative_t<

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

        > const &&get(const std::variant<Types...> &&v);

template <class T, class... Types>

constexpr T &get(std::variant<Types...> &v);

template <class T, class... Types>

constexpr T &&get(std::variant<Types...> &&v);
(2)(since C++ 17)

    template <class T, class... Types>

    constexpr const T &get(const std::variant<Types...> &v);

template <class T, class... Types>

constexpr const T &&get(const std::variant<Types...> &&v);

1) Index-based value accessor: If v.index() == I, returns a reference to the value stored in v. Otherwise, throws std::bad_variant_access. The call is ill-formed if I is not a valid index in the variant.
2) Type-based value accessor: If v holds the alternative T, returns a reference to the value stored in v. Otherwise, throws std::bad_variant_access. 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
v – a variant

Return value

Reference to the value stored in the variant.

Exceptions

1,2) Throws std::bad_variant_access on errors.

Example

// Run this code

#include <variant>

#include <string>
int main()

{
    std::variant<int, float> v{12}, w;
    int i = std::get<int>(v);
    w = std::get<int>(v);
    w = std::get<0>(v); // same effect as the previous line
    //  std::get<double>(v); // error: no double in [int, float]

    //  std::get<3>(v);      // error: valid index values are 0 and 1
    try {
        std::get<float>(w); // w contains int, not float: will throw
    } catch (std::bad_variant_access &) {
    }
}

See also

get_if obtains a pointer to the value of a pointed-to variant given the index or the type (if unique), returns null on error
                     (function template)
(C++17)
                     tuple accesses specified element
std::get(std::tuple) (function template)
                     accesses an element of an array
std::get(std::array) (function template)
std::get(std::pair) accesses an element of a pair
                     (function template)
(C++11)