C++ enum 枚举

枚举不但定义了整数常量集，而且还把它们聚集成组。
 enum open_modes {input, output, append};
 默认地，第一个枚举成员赋值为0，后面的每个枚举成员赋的值比前面的大1。
void main()
{
 enum open_modes {input, output, append};
 enum Forms {shape = 1, sphere, cylinder, polygon};

 cout<<sizeof(open_modes)<<endl;
 cout<<sizeof(Forms)<<endl;
 cout<<sizeof(int)<<endl;

 //open_modes om = 1;// error
 open_modes om = (open_modes)1;
 int t = open_modes::input;
 int k = om;
 cout<<om<<" "<<t<<" "<<k<<endl;
 
 open_modes om2 = (open_modes)4;
 cout<<om2<<endl;
}