問題描述
如果我分配一個 Derived 類的對象(具有 Base 的基類)，并將指向該對象的指針存儲在指向基類的變量中類，如何訪問 Derived 類的成員?
If I allocate an object of a class Derived (with a base class of Base), and store a pointer to that object in a variable that points to the base class, how can I access the members of the Derived class?
這是一個例子:
class Base
{
public:
int base_int;
};
class Derived : public Base
{
public:
int derived_int;
};
Base* basepointer = new Derived();
basepointer-> //Access derived_int here, is it possible? If so, then how?
推薦答案
不，您不能訪問 derived_int 因為 derived_int 是 Derived 的一部分，而 basepointer 是指向 Base 的指針.
No, you cannot access derived_int because derived_int is part of Derived, while basepointer is a pointer to Base.
你可以反過來做:
Derived* derivedpointer = new Derived;
derivedpointer->base_int; // You can access this just fine
派生類繼承基類的成員，而不是相反.
Derived classes inherit the members of the base class, not the other way around.
但是，如果您的 basepointer 指向 Derived 的實例，那么您可以通過強制轉換訪問它:
However, if your basepointer was pointing to an instance of Derived then you could access it through a cast:
Base* basepointer = new Derived;
static_cast<Derived*>(basepointer)->derived_int; // Can now access, because we have a derived pointer
請注意，您需要先將繼承更改為 public:
Note that you'll need to change your inheritance to public first:
class Derived : public Base
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