h*****g
发帖数: 312 | 1 class Base{
public:
Base();
virtual ~Base();
};
class Derived: protected Base{
public:
virtual ~Derived();
};
int _tmain(int argc, _TCHAR* argv[])
{
Base *pd = new Derived;
getchar();
return 0;
}
Referring to the sample code above, which one of the following statements is
true?
A.
A constructor needs to be added to Derived class.
B.
The pointer returned by new cannot be type cast from Derived* to Base*.
C.
A pointer to a Base class cannot point to an instance of a Derived class.
D.
Derived class cannot have a virtual destructor.
E.
The code compiles with no errors.
答案是B。但查了半天没看懂为啥？看懂的能不能给详细的解释一下？难道是要call
baseclass的ctr to cast from Derived* to Base*?
class A
{
public:
void f{};
protected:
A(){};
A(const A&){}
}
Referring to the sample code above, why are the default and copy
constructors declared as protected?
A.
To ensure that instances of A can only be created by subclasses of A
B.
To ensure that instances of A cannot be created via new by a more derived
class
C.
To ensure that instances of A cannot be copied
D.
To ensure that A cannot be instantiated on the stack
E.
To ensure that A cannot be used as a base class
答案给的是A。 那如何由子类去创造 A 的object 呢？A * p= new subclass 可行吗？
能call A的ctr吗？ | N***m
发帖数: 4460 | 2 is it because of protected inheritance?
【在 h*****g 的大作中提到】
: class Base{
: public:
: Base();
: virtual ~Base();
: };
: class Derived: protected Base{
: public:
: virtual ~Derived();
: };
: int _tmain(int argc, _TCHAR* argv[])
|
|
