使用函式指標時，指標可以像函式名一樣，直接加括號和引數列表呼叫；也可先解引用再呼叫

//include directories...
  using namespace std;
  void testFun()
  {
      cout<<"this is a test"<<endl;
  }
  int main(int argc,char**argv)
  {
      auto *pFun=testFun;
     pFun();//or (*pFun)() is also fine   
 }

但是使用類指標時不可以

//header files...
  using namespace std;
  class A
  {
  private:
      int a;
  public:
      A(int a_):a(a_){}
      void operator(){cout<<a<<endl;}
 };
 int main(int argc,char** argv)
 {
     A a1(5);
     A *pA=new A(7);
     a1();//correct using operator() function
     (*pA)();//pA() is not correct
 }