C++ Q96: function inheritance - 未名空间MITBBS历史存档

国际科技财经博客移民网络热点娱乐民生时事公众号

Redian新闻

>未名空间

>JobHunting - 待字闺中

C++ Q96: function inheritance

C++ Q96: function inheritance# JobHunting - 待字闺中

c*e2011-10-16 07:10

1 楼

Error information in the following code is Error: equals is not a member of
B.
My question: Why equals() is not a member of B but print() is?
While this seems obvious, what is the general rule that a function will be
inherited?
#include
using namespace std;
class A {
public:
bool equal(A a) { return true; }
void print() { cout << "print\n"; }
};
class B: public A {};
int main() {
B b;
bool x = b.equals(b);
b.print();
return 0;
}

b*c2011-10-16 07:10

2 楼

。。。。。
因为equal(A)而不是equal(B)，而且b是B啊

S*I2011-10-16 07:10

3 楼

because "equal" is inherited, but "equals" is not.

of

【在 c**********e 的大作中提到】

: Error information in the following code is Error: equals is not a member of
: B.
: My question: Why equals() is not a member of B but print() is?
: While this seems obvious, what is the general rule that a function will be
: inherited?
: #include
: using namespace std;
: class A {
: public:
: bool equal(A a) { return true; }

b*c2011-10-16 07:10

4 楼

哦哦哦，另外一个问题，B不需要显式转换A吗？？

【在 S**I 的大作中提到】

: because "equal" is inherited, but "equals" is not.
:
: of

r*y2011-10-16 07:10

5 楼

you defined equal instead of equals

of

【在 c**********e 的大作中提到】

r*y2011-10-16 07:10

6 楼

B will slice down to A

【在 b*****c 的大作中提到】

: 哦哦哦，另外一个问题，B不需要显式转换A吗？？

c*e2011-10-16 07:10

7 楼

Faint. I made such a low level mistake. Then what is the output of the
following code?
#include
using namespace std;
class A {
public:
bool equals(A a) { return data==a.data; }
void setData(int input) { data=input; }
private:
int data;
};
class B: public A {};
void main() {
A a;
a.setData(7);
B b;
b.setData(7);
cout << a.equals(b) << endl;
cout << b.equals(a) << endl;
}

t*n2011-10-16 07:10

8 楼

1
1

【在 c**********e 的大作中提到】

: Faint. I made such a low level mistake. Then what is the output of the
: following code?
: #include
: using namespace std;
: class A {
: public:
: bool equals(A a) { return data==a.data; }
: void setData(int input) { data=input; }
: private:
: int data;

b*c2011-10-16 07:10

9 楼

//true
1
1