Run Time Type Information - C++ Questions and Answers

This set of C++ Programming Multiple Choice Questions & Answers (MCQs) focuses on “Run Time Type Information”.

1. What is the Run-Time Type Information?
a) Information about an object’s data type at runtime
b) Information about the variables
c) Information about the given block
d) Information about the functions
View Answer

Answer: a
Explanation: With the help of RTTI, We can get the information about the data type at the runtime.

2. Which operators are part of RTTI?
a) dynamic_cast()
b) typeid
c) both dynamic_cast<> & typeid
d) dynamic_cast[]
View Answer

Answer: c
Explanation: The dynamic_cast<> operation and typeid operator in C++ are part of RTTI.

3. To which type of class, We can apply RTTI?
a) Encapsulation
b) Polymorphic
c) Derived
d) Static
View Answer

Answer: b
Explanation: RTTI is available only for classes which are polymorphic, which means they have at least one virtual method.

4. What will be the output of the following C++ code?

```
    #include <iostream>
```
```
    #include <exception>
```
```
    using namespace std;
```

    class base { virtual void dummy() {} };

    class derived: public base { int a; };

```
    int main () 
```
```
    {
```
```
        try 
```
```
        {
```
```
            base * pba = new derived;
```
```
            base * pbb = new base;
```
```
            derived * pd;
```

            pd = dynamic_cast<derived*>(pba);

```
            if (pd == 0) 
```

                cout << "Null pointer on first type-cast" << endl;

            pd = dynamic_cast<derived*>(pbb);

```
            if (pd == 0) 
```

                cout << "Null pointer on second type-cast" << endl;

```
        } 
```
```
        catch (exception& e) 
```
```
        {
```

            cout << "Exception: " << e.what();

```
        }
```
```
        return 0;
```
```
    }
```

a) Null pointer on first type-cast
b) Null pointer on second type-cast
c) Exception
d) Null pointer on third type-cast
View Answer

Answer: b
Explanation: In this program, We apply the dynamic cast to pd. Based on the value in the pd, it produces the output.
Output:

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$ g++ rtti.cpp
$ a.out
Null pointer on second type-cast

5. What will be the output of the following C++ code?

```
    #include <iostream>
```
```
    #include <typeinfo>
```
```
    using namespace std;
```
```
    int main () 
```
```
    {
```
```
        int * a;
```
```
        int b;
```
```
        a = 0; b = 0;
```
```
        if (typeid(a) != typeid(b))
```
```
        {
```
```
            cout << typeid(a).name();
```
```
            cout << typeid(b).name();
```
```
        }
```
```
        return 0;
```
```
    }
```

a) Pi
b) i
c) Both pi & i
d) f
View Answer

Answer: c
Explanation: In this program, We are finding the typeid of the given variables.
Output:

$ g++ rtti1.cpp
$ a.out
Pii

6. What will be the output of the following C++ code?

```
    #include <iostream>
```
```
    #include <typeinfo>
```
```
    #include <exception>
```
```
    using namespace std;
```
```
    class base 
```
```
    { 
```
```
        virtual void f(){} 
```
```
    };
```
```
    class derived : public base {};
```
```
    int main () 
```
```
    {
```
```
        try 
```
```
        {
```
```
            base* a = new base;
```
```
            base* b = new derived;
```

            cout << typeid(*a).name() << '\t';

```
            cout << typeid(*b).name();
```
```
        } 
```
```
        catch (exception& e) 
```
```
        { 
```

            cout << "Exception: " << e.what() << endl;

```
        }
```
```
        return 0;
```
```
    }
```

a) base*
b) derived*
c) 4base and 7derived
d) Exception:derived
View Answer

Answer: c
Explanation: In this program, We apply the typeid to the polymorphic class.
Output:

$ g++ rtti2.cpp
$ a.out
4base    7derived

7. What will be the output of the following C++ code?

```
    #include <typeinfo>
```
```
    #include <iostream>
```
```
    using namespace std;
```
```
    class A
```
```
    {
```
```
        public:
```
```
        virtual ~A();
```
```
    };
```
```
    int main() 
```
```
    {
```
```
        A* a = NULL;
```
```
        try 
```
```
        {
```

            cout << typeid(*a).name() << endl;

```
        }
```
```
        catch (bad_typeid)
```
```
        {
```

            cout << "Object is NULL" << endl;

```
        }
```
```
    }
```

a) int
b) float
c) double
d) object is NULL
View Answer

Answer: d
Explanation: In this program, We are using the bad typeid() for a. So it is arising an exception.
Output:

$ g++ rtti3.cpp
$ a.out
object is NULL

8. What will be the output of the following C++ code?

```
    #include <iostream>
```
```
    using namespace std;
```
```
    struct A 
```
```
    {
```
```
        virtual void f()  
```
```
        { 
```
```
            cout << "Class A" << endl; 
```
```
        }
```
```
    };
```
```
    struct B : A 
```
```
    {
```
```
        virtual void f() 
```
```
        { 
```
```
            cout << "Class B" << endl;
```
```
        }
```
```
    };
```
```
    struct C : A 
```
```
    {
```
```
        virtual void f() 
```
```
        {
```
```
            cout << "Class C" << endl; 
```
```
        }
```
```
    };
```
```
    void f(A* arg) 
```
```
    {
```
```
        B* bp = dynamic_cast<B*>(arg);
```
```
        C* cp = dynamic_cast<C*>(arg);
```
```
        if (bp)
```
```
            bp -> f();
```
```
        else if (cp)
```
```
            cp -> f();
```
```
        else
```
```
            arg -> f();  
```
```
    };
```
```
    int main() 
```
```
    {
```
```
        A aobj;
```
```
        C cobj;
```
```
        A* ap = &cobj;
```
```
        A* ap2 = &aobj;
```
```
        f(ap);
```
```
        f(ap2);
```
```
    }
```

a) Class C
b) Class A
c) Both Class C & A
d) Class D
View Answer

Answer: c
Explanation: In this program, We applied the dynamic casting to structure and produced the output.
Output:

$ g++ rtti4.cpp
$ a.out
Class C
Class A

9. What is meant by type_info?
a) Used to hold the type information returned by the typeid operator
b) Used to hold the type information returned by the dynamic_cast
c) Used to hold the type information returned by the static_cast
d) Used to hold the type information returned by the static_id
View Answer

Answer: a
Explanation: type_info is used to hold the type information returned by the typeid operator.

10. At which time does the static_cast can be applied?
a) Compile-time construct
b) Runtime construct
c) Both Compile-time & Runtime construct
d) Runtime deconstruct
View Answer

Answer: a
Explanation: Static_cast can be applied to only compile-time construct and not during run time construct.

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