Output of C++ Program | Set 16

　　Predict the output of following C++ programs.

Question 1

 1 #include<iostream>
 2 using namespace std;
 3
 4 class Base
 5 {
 6 public:
 7     int fun()
 8     {
 9         cout << "Base::fun() called";
10     }
11     int fun(int i)
12     {
13         cout << "Base::fun(int i) called";
14     }
15 };
16
17 class Derived: public Base
18 {
19 public:
20     int fun(char x)
21     {
22         cout << "Derived::fun(char ) called";
23     }
24 };
25
26 int main()
27 {
28     Derived d;
29     d.fun();
30     return 0;
31 }

　　Output: Compiler Error.
　　In the above program, fun() of base class is not accessible in the derived class. If a derived class creates a member method with name same as one of the methods in base class, then all the base class methods with this name become hidden in derived class.

Question 2

 1 #include<iostream>
 2 using namespace std;
 3 class Base
 4 {
 5 protected:
 6     int x;
 7 public:
 8     Base (int i)
 9     {
10         x = i;
11     }
12 };
13
14 class Derived : public Base
15 {
16 public:
17     Derived (int i):x(i)
18     {
19     }
20     void print()
21     {
22         cout << x ;
23     }
24 };
25
26 int main()
27 {
28     Derived d(10);
29     d.print();
30 }

　　Output: Compiler Error
　　In the above program, x is protected, so it is accessible in derived class. Derived class constructor tries to use initializer list to directly initialize x, which is not allowed even if x is accessible. The members of base class can only be initialized through a constructor call of base class.

　　Following is the corrected program.

 1 #include<iostream>
 2 using namespace std;
 3 class Base
 4 {
 5 protected:
 6     int x;
 7 public:
 8     Base (int i)
 9     {
10         x = i;
11     }
12 };
13
14 class Derived : public Base
15 {
16 public:
17     Derived (int i):Base(i)
18     {
19     }
20     void print()
21     {
22         cout << x;
23     }
24 };
25
26 int main()
27 {
28     Derived d(10);
29     d.print();
30 }

　　Output:

　　10

　　Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

　　转载请注明：http://www.cnblogs.com/iloveyouforever/

　　2013-11-27　　16:34:25