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std::underlying_type

STD：：基础[医]类型

Defined in header ​​
template< class T > struct underlying_type;​(since C++11)

如果T是一个完整的枚举类型，提供一个成员类型type的基础类型。T...

否则，行为就没有定义。

成员类型

NameDefinition
typethe underlying type of T

帮助者类型

template< class T > using underlying_type_t = typename underlying_type::type;​(since C++14)

注记

各枚举类型有一个底层类型也可以是。

  • 显式指定%28范围和非作用域枚举%29。

  • 省略，在这种情况下是int对于作用域枚举或实现定义的整数类型，该类型能够表示非作用域枚举%29的枚举%28的所有值。

缺陷报告

以下行为更改缺陷报告追溯应用于先前发布的C++标准。

DRApplied toBehavior as publishedCorrect behavior
LWG 2396C++11incomplete enumeration types were allowedcomplete enumeration type required

例

二次

#include <iostream>
#include <type_traits>
 
enum e1 {};
enum class e2: int {};
 
int main() {
    bool e1_type = std::is_same<
        unsigned
       ,typename std::underlying_type<e1>::type
    >::value; 
 
    bool e2_type = std::is_same<
        int
       ,typename std::underlying_type<e2>::type
    >::value;
 
    std::cout
    << "underlying type for 'e1' is " << (e1_type?"unsigned":"non-unsigned") << '\n'
    << "underlying type for 'e2' is " << (e2_type?"int":"non-int") << '\n';
}

二次

产出：

二次

underlying type for 'e1' is unsigned
underlying type for 'e2' is int

二次

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在CreativeCommonsAttribution下授权-ShareAlike未移植许可v3.0。

http：//en.cppreference.com/w/cpp/type/bob[医]类型

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