std::get

STD：：获取%28 std：：变体%29

Defined in header
	(1)	(since C++17)
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
template <std::size_t I, class... Types> constexpr std::variant_alternative_t< I, std::variant<Types...> > const&& get(const std::variant<Types...>&& v
	(2)	(since C++17)
template <class T, class... Types> constexpr T& get(std::variant<Types...>& v
template <class T, class... Types> constexpr T&& get(std::variant<Types...>&& v
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%29基于索引的值访问器：如果v.index() == I中存储的值的引用。v.否则，抛出std::bad_variant_access...打电话是不正确的，如果I在变体中不是有效的索引。

基于2%29类型的值访问器：如果v持有另一种选择T中存储的值的引用。v.否则，抛出std::bad_variant_access...打电话是不正确的，如果T的唯一元素Types......

参数

I	-	index to look up
Type	-	unique type to look up
v	-	a variant

返回值

引用存储在变体中的值。

例外

1，2%29投std::bad_variant_access关于错误。

例

二次

#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&) {}
}

二次

另见

get_if (C++17)	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)
std::get(std::tuple)	tuple accesses specified element (function template)
std::get(std::array)	accesses an element of an array (function template)
std::get(std::pair) (C++11)	accesses an element of a pair (function template)

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