c++枚举的底层类型是什么?

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

这个问题可能在其他地方得到了回答，但我找不到合适的回答。

I have this code:

我有这段代码:

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.

这是遗留问题，我必须通过添加一些新值来修改它。问题是每个值都必须是唯一的位，所以它们可以是或合并到位图。

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

这些值是使用#x## hex格式设置的，但是我想知道这是否是它可以存储的最大值?如果我将代码更改为，会有什么影响

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,   
};

4 个解决方案

#1

From Standard C++ 7.2/5:

从标准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.

枚举的底层类型是一个完整类型，它可以表示枚举中定义的所有枚举数值。是实现定义整型作为底层为枚举类型,除了底层不得大于int类型除非enu表示的价值——merator不能适应int或unsigned int。如果enumerator-list是空的,底层的类型是枚举仿佛一个枚举器,值0。应用于enu- meration类型、枚举类型对象或枚举器的sizeof()的值是应用于底层类型的sizeof()的值。

#2

The type of a C++ enum is the enum itself. Its range is rather arbitrary, but in practical terms, its underlying type is an int.

c++枚举类型是enum本身。它的范围相当随意，但实际上，它的底层类型是int类型。

It is implicitly cast to int wherever it's used, though.

不过，无论在哪里使用它，它都被隐式地转换为int。

C++11 changes

This has changed since C++11, which introduced typed enums. An untyped enum now is defined as being at least the width of int (and wider if larger values are needed). However, given a typed enum defined as follows:

自从c++ 11引入了类型枚举之后，这种情况已经发生了变化。未类型化的枚举现在被定义为至少是int的宽度(如果需要更大的值，则更宽)。但是，给定一个类型的enum，定义如下:

enum name : type {};

An enumeration of type name has an underlying type of type. For example, enum : char defines an enum the same width as char instead of int.

类型名称的枚举类型有一个底层类型。例如，enum: char定义了与char而不是int相同的宽度。

Further, an enum can be explicitly scoped as follows:

此外，枚举可以显式地限定如下:

enum class name : type {
    value = 0,
    // ...
};

(Where name is required, but type is optional.) An enum declared this way will no longer implicitly cast to its underlying type (requiring a static_cast<>) and values must be referenced with a fully-qualified name. In this example, to assign value to a enum variable, you must refer to it as name::value.

(需要名称，但类型是可选的)以这种方式声明的enum将不再隐式地转换到它的底层类型(需要static_cast<>)，并且必须使用完全限定的名称引用值。在本例中，要为enum变量赋值，必须将其引用为name::value。

#3

IIRC its represented as int in memory. But gcc has switch -fshort-enum to make it a shortest integer type that fits all the values, if you need to save space. Other compilers will have something similar.

IIRC在内存中表示为int。但是gcc有开关-fshort-enum，如果您需要节省空间，可以将它设置为适合所有值的最短整数类型。其他编译器也会有类似的情况。

#4

The underlying type is the smallest signed integer fitting the biggest/smallest value of your enum.

底层类型是最小的带符号整数，适合枚举的最大/最小值。