C++多态、不完全向下转型
我有一个数组，其中包含对平淡基类型的引用，我们将其称为Object。
我从 Object 派生了 Class1，从 Class1 派生了 Class2。
#include <vector>
class Object {};
class Class1 : public Object {
public:
virtual std::string ToString() {return "it is 1";}
};
class Class2 : public Class1 {
public:
virtual std::string ToString() {return "it is 2";}
};
int _tmain(int argc, _TCHAR* argv[])
{
std::vector<Object *> myvec;
myvec.push_back(new Class2());
printf("%s", (static_cast<Class1*>(myvec[0]))->ToString().c_str());
return 0;
}
我通过从 Object * 转换为 Class1 * 来调用 ToString()
printf("%s", (static_cast<Class1*>(myvec[0]))->ToString().c_str());
我的问题是，当对象为事实上是 Class2 但不是专门向下转换？ virtual 关键字是否达到预期效果？
I have an array which holds references to a bland base type, let's call it Object.
I have derived Class1 from Object and Class2 from Class1.
#include <vector>
class Object {};
class Class1 : public Object {
public:
virtual std::string ToString() {return "it is 1";}
};
class Class2 : public Class1 {
public:
virtual std::string ToString() {return "it is 2";}
};
int _tmain(int argc, _TCHAR* argv[])
{
std::vector<Object *> myvec;
myvec.push_back(new Class2());
printf("%s", (static_cast<Class1*>(myvec[0]))->ToString().c_str());
return 0;
}
I call ToString() by casting from Object * to Class1 * like so
printf("%s", (static_cast<Class1*>(myvec[0]))->ToString().c_str());
My question is, will this output 1 or 2 when the object is in fact of Class2 but not down cast to that specifically? Is the virtual keyword having the intended effect?
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它应该调用 Class2 的虚函数，因为该对象属于该类型。
请记住：虚函数的目的是调用实际类的函数，而不是指针/引用当前显示的类的函数。
It should call
Class2's virtual function, since the object is of that type.Remember: the purpose of a virtual function is to call the actual class's function, not the function for the class the pointer/reference currently appears to be.
当我第一次回答你的问题时，我有点误解了你的问题，关于恶魔和你的鼻孔。
virtual关键字将达到预期的效果。也就是说，您将看到 2。尽管您已转换为Class1，但 vtable 将发挥其魔力。I slightly misread your question when I first answered, regarding demons and your nostrils.
The
virtualkeyword will have it's intended effect. That is, You will see 2. Although you have casted toClass1, the vtable will work it's magic.首先，这不是一个安全的转换。但假设 myvec[i] 是您要转换到的对象的指针，那么它将调用该类的适当方法。
First, this is not a safe cast. But assuming that
myvec[i]is a pointer the an object you are casting to, then it will call the appropriate method for that class.