定义一个CPU类，包含等级（rank)、频率（frequency) 、电压（voltage) 等属性 ，有两 个公有成员函数run、stop。其中， 为枚举类型 CPU_Rank，定义为 enum CPU_Rank{P1=1,P2,P3,P4,P5,P6,P7}，frequency为单位是MHz的整型数，voltage为浮点型的电压值。观察构造函数和析构函数的调用顺序。-CPU define a class that contains the rank (rank), frequency (frequency), voltage (voltage) and other property, there are two public member functions run, stop. Among them, as enumerated types CPU_Rank, defined as enum CPU_Rank {P1 = 1, P2, P3, P4, P5, P6, P7}, frequency as the unit is MHz integer number, voltage is the voltage value of a floating-point type. Observation call sequence constructors and destructors.