如何让test.calculate中的函数指针赋值(可能还有其他)起作用？#includeclasstest{inta;intb;intadd(){returna+b;}intmultiply(){returna*b;}public:intcalculate(charoperatr,intoperand1,intoperand2){int(*opPtr)()=NULL;a=operand1;b=operand2;if(operatr=='+')opPtr=this.*add;if(operatr=='*')opPtr=this.*multiply;returnopPtr();}};in