5
我嘗試實現多態函子對象（純粹的抽象基類和子類）僅用於理解目的。我的目標是創建許多基類的對象，它們使用純虛函數的不同實現。C++瞭解函子多態性
當我創建基類的指針並將其設置爲等於新的子類時，我無法將該對象作爲函數調用。錯誤是：
main.cpp:29:7: error: ‘a’ cannot be used as a function
下面是代碼：
#include <iostream>
class foo{
public:
virtual void operator()() = 0;
virtual ~foo(){}
};
class bar: public foo{
public:
void operator()(){ std::cout << "bar" << std::endl;}
};
class car: public foo{
public:
void operator()(){ std::cout << "car" << std::endl;}
};
int main(int argc, char *argv[])
{
foo *a = new bar;
foo *b = new car;
//prints out the address of the two object:
//hence I know that they are being created
std::cout << a << std::endl;
std::cout << b << std::endl;
//does not call bar() instead returns the error mentioned above
//I also tried some obscure variation of the theme:
//*a(); *a()(); a()->(); a->(); a()();
//just calling "a;" does not do anything except throwing a warning
a();
//the following code works fine: when called it print bar, car respectivly as expected
// bar b;
// car c;
// b();
// c();
delete b;
delete a;
return 0;
}
我目前的理解是，「富*一個」存儲如由在一個功能對象「BAR」的地址（ cout聲明）。因此，取消引用它「* a」應該提供對「a」指向的函數的訪問權限，「* a（）」應該調用它。
但它沒有。誰能告訴我爲什麼？