修改SuperVar以便所有vartype代码前有#ifdef,让vartype成为一个常规的public枚举类型(没有实例),修改print(),使它要求vartype参数能告诉它做什么.
#include<iostream>
using namespace std;

class SuperVar{
    enum{
        character,
        integer,
        floating_point
    }vartype;//define one
    union{     //anonymous union
        char c;
        int i;
        float f;
    };
public:
    SuperVar(char ch);
    SuperVar(int ii);
    SuperVar(float ff);
    void print();
};
SuperVar::SuperVar(char ch){
    vartype=character;
    c=ch;
}
SuperVar::SuperVar(int ii){
    vartype=integer;
    i=ii;
}
SuperVar::SuperVar(float ff){
    vartype=floating_point;
    f=ff;
}
void SuperVar::print(){
    switch(vartype){
    case character:
        cout<<"character="<<c<<endl;
        break;
    case integer:
        cout<<"integer="<<i<<endl;
        break;
    case floating_point:
        cout<<"float="<<f<<endl;
        break;
    }
}
int main(){
    SuperVar A('c'),B(12),C(1.44F);
    A.print();
    B.print();
    C.print();
}///:~