Complete the definition of the member function in the following class. #include #include using namespace std; class str {private: char *st; public: str(char *a) {set(a); } str & operator=(____) {delete st; set(a.st); return *this; } void show(){cout< ~str(){delete st;} void set(char *s)// 初始化st {_____ strcpy(st,s); } }; void main() {str s1("he"),s2("she"); s1.show(),s2.show(); s2=s1; s1.show(),s2.show();}