枚举的范围 [英] the range of enum

问题描述

根据<< C ++编程语言>>：

enum flag {x = 1，y = 2，z = 4，e = 8}; //范围0:15
...
标志f4 =标志（99）; //未定义：99不在标志范围内

但以下代码的结果为99.


// --------------------------------------------------

#include" iostream"

int main（int argc，char * argv []）

{

enum flag {x = 1，y = 2，z = 4，e = 8};


flag f1 = flag（99）;


std :: cout<< f1<< std :: endl;


返回0;

}


// --------------------------------------- -------------

编译器是否将枚举类型视为整数类型？那么enum范围的含义是什么？

解决方案

Vane写道：
< blockquote class =post_quotes>根据<< C ++编程语言>>：

enum flag {x = 1，y = 2，z = 4，e = 8 }; //范围0:15
...
标志f4 =标志（99）; // undefined：99不在flag的范围内

但以下代码的结果为99。

"未定义"意思是结果可以是任何东西。这包括

值99.

这是一个合适的答案，因为有些编译器已经实现。

但是，编译器应该产生错误：


flag f4 = flag（99）;


此时，说undefined意味着你做的任何事情都没关系，不是好的。
似乎是合理的。


问候，

博士Z. < br $> b $ b首席科学家
zo****@ZHMicro.com
http://www.zhmicro.com
http://distributed-software.blogspot.com

Zorro写道：

这是一个合适的答案，因为有些编译器已经实现。
然而，编译器应该产生错误：

flag f4 = flag（99）;

不，它不应该。这是一个强制转换，并将一个整数转换为枚举是允许的

。如果是这样会有所不同：


flag f4 = 99;

According to <<C++ Programming Language>>:

enum flag { x = 1, y = 2, z = 4, e = 8 }; //range 0:15
...
flag f4 = flag(99); // undefined : 99 is not within the range of flag

But the following codes has result 99.

//--------------------------------------------------
#include "iostream"

int main(int argc, char* argv[])
{
enum flag{ x = 1, y = 2, z = 4, e = 8 };

flag f1 = flag( 99 );

std::cout<<f1<<std::endl;

return 0;
}

//----------------------------------------------------
Whether the compiler treats enum type as integral type? Then what''s the
meaning of the range of enum?

解决方案

Vane wrote:

According to <<C++ Programming Language>>:

enum flag { x = 1, y = 2, z = 4, e = 8 }; //range 0:15
...
flag f4 = flag(99); // undefined : 99 is not within the range of flag

But the following codes has result 99.

"Undefined" means "the result can be anything". And this includes a
value of 99.

This is an appropriate answer, as some compilers are implemented.
However, the compiler should have produced error at:

flag f4 = flag(99);

At this point, saying undefined means anything you do is OK, does not
seem justifiable.

Regards,
Dr. Z.
Chief Scientist
zo****@ZHMicro.com
http://www.zhmicro.com
http://distributed-software.blogspot.com

Zorro wrote:

This is an appropriate answer, as some compilers are implemented.
However, the compiler should have produced error at:

flag f4 = flag(99);

No, it shouldn''t. This is a cast, and casting an integer into an enum is
allowed. It would be different if it were:

flag f4 = 99;

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