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.
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问题:
回答1:
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;
};
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).