什么是c ++枚举的基础类型？ [英] What is the underlying type of a c++ enum?

问题描述

我有这个代码：

 枚举enumWizardPage 
 {
 WP_NONE = 0x00，
 WP_CMDID = 0x01，
 WP_LEAGUES = 0x02，
 WP_TEAMS = 0x04 ，
 WP_COMP = 0x08，
 WP_DIVISIONS = 0x10，
 WP_FORMULAS = 0x20，
 WP_FINISHED = 0x40，
}; 
  

哪些是遗产，我必须通过添加几个新值来修改它。
问题是每个值必须是一个唯一的位，所以它们可能被组合到一个位图。

这些值是使用＃x ##十六进制格式设置的，但我想知道这是否可以存储的最大值？
如果我将代码更改为

 枚举enumWizardPage 
 { 
 WP_NONE = 0x0000，
 WP_CMDID = 0x0001，
 WP_LEAGUES = 0x0002，
 WP_TEAMS = 0x0004，
 WP_COMP = 0x0008，
 WP_DIVISIONS = 0x0010，
 WP_FORMULAS = 0x0020，
 WP_FINISHED = 0x0040，
}; 
  

解决方案

从标准C ++ 7.2 / 5：

枚举的基础类型是一个整数类型，可以表示枚举中定义的所有枚举值
。实现定义哪个整数类型用作枚举的基础类型
，除了底层类型不应大于int，除非enu-
merator的值不能适合于int或unsigned int。如果枚举器列表为空，则底层类型为
，就像枚举具有单个枚举值为0的值一样。sizeof（）的值应用于enu-
meration类型，枚举对象类型或枚举器是应用于
底层类型的sizeof（）的值。

This may have been answered elsewhere but I could not find a suitable response.

I have this code:

enum enumWizardPage
{
    WP_NONE = 0x00,  
    WP_CMDID = 0x01,    
    WP_LEAGUES = 0x02,  
    WP_TEAMS = 0x04,    
    WP_COMP = 0x08, 
    WP_DIVISIONS = 0x10,
    WP_FORMULAS = 0x20, 
    WP_FINISHED = 0x40, 
};

Which is legacy and I have to modify it by adding a few new values. The issue is each value must be a unique bit so they may be OR combined to a bitmap.

The values are set using the #x## hex format, but I'm wondering if this is the max it can store? What will be the effect, if any, if I change my code to

enum enumWizardPage
{
    WP_NONE = 0x0000,  
    WP_CMDID = 0x0001,  
    WP_LEAGUES = 0x0002,    
    WP_TEAMS = 0x0004,  
    WP_COMP = 0x0008,   
    WP_DIVISIONS = 0x0010,
    WP_FORMULAS = 0x0020,   
    WP_FINISHED = 0x0040,   
};

解决方案

From Standard C++ 7.2/5:

The underlying type of an enumeration is an integral type that can represent all the enumerator values defined in the enumeration. It is implementation-defined which integral type is used as the underlying type for an enumeration except that the underlying type shall not be larger than int unless the value of an enu- merator cannot fit in an int or unsigned int. If the enumerator-list is empty, the underlying type is as if the enumeration had a single enumerator with value 0. The value of sizeof() applied to an enu- meration type, an object of enumeration type, or an enumerator, is the value of sizeof() applied to the underlying type.

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