sizeof(enum_type)

最新推荐文章于 2025-07-06 01:05:42 发布

转载最新推荐文章于 2025-07-06 01:05:42 发布 · 93 阅读

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#c/c++ #面试

博客围绕C/C++面试要点展开，提及防止头文件重复定义的方法，即使用#ifndef、#def、#enddef，还强调野指针free后要置为NULL。同时详细探讨了枚举类型的sizeof计算，对比了C和C++中枚举器类型的差异，并给出不同枚举示例下的范围及sizeof情况。

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面试时候碰到。还有就是如何防止头文件重复定义，用
#ifndef
#def
#enddef
野指针，free后再置为NULL。

sizeof(enum_type)

C++标准p692:
In C++,the type of an enumerator is its enumeration. In C,tye type of an enumerator is int.
   enum e{A};
   sizeof(A)==sizeof(int)   //in C
   sizeof(A)==sizeof(e)    //In C++
   /*and sizeof(int) is not nessary equal to sizeof(e) */

那么怎么计算enumerator的sizeof?

the c++ programming language 3rd edition 4.8

The range of an enumeration holds all the enumeration’s enumerator values rounded up to the nearest larger binary power minus 1. The range goes down to 0 if the smallest enumerator is nonnegative and to the nearest lesser negative binary power if the smallest enumerator is negative. This defines the smallest bitfield capable of holding the enumerator values. For example:
   enum e1 { dark, light}; / / range 0:1
   enum e2 { a = 3, b = 9}; / / range 0:15
   enum e3 {min= 10, max = 1000000 }; / / range 1048576:1048575

The sizeof an enumeration is the sizeof some integral type that can hold its range and not larger than sizeof(int), unless an enumerator cannot be represented as an int or as an unsigned int. For example, sizeof(e1) could be 1 or maybe 4 but not 8 on a machine where sizeof(int)==4.

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