联盟对当前使用中的成员进行了测试 [英] Union tested for current member in use

问题描述

工会是否具有控制结构来测试当前正在使用哪个成员(或者是否有成员)?我问这个问题是因为未定义的行为永远都不是程序中的好事.

Do unions have a control structure to test which member is currently in use (or if it has any at all)? I'm asking this because undefined behavior is never a good thing to have in your program.

推荐答案

否，现成的机制不存在.您必须自己照顾自己. 通常的方法是将union包装在struct中:

No, no such mechanism exists off-the-shelf. You'll have to take care of that yourself. The usual approach is wrapping the union in a struct:

struct MyUnion
{
   int whichMember;
   union {
      //whatever
   } actualUnion;
};

所以您有MyUnion x;，并且x.whichMember告诉您正在使用x.actualUnion的哪个字段(不过您必须实现功能).

So you have MyUnion x; and x.whichMember tells you which field of x.actualUnion is in use (you have to implement the functionality though).

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