1) class Sample
{
public:
int *ptr;
Sample(int i)
{
ptr = new int(i);
}
~Sample()
{
delete ptr;
}
void PrintVal()
{
cout << "The value is "
<< *ptr;
}
};
void
SomeFunc(Sample x)
{
cout <<
"Say i am in someFunc " << endl;
}
int main()
{
Sample s1= 10;
SomeFunc(s1);
s1.PrintVal();
}
Answer:
Say i am in
someFunc
Null pointer
assignment(Run-time error)
Explanation:
As the object is
passed by value to SomeFunc the
destructor of the object is called when the control returns from the function.
So when PrintVal is called it meets up with ptr
that has been freed.The solution is to pass the Sample object by
reference to SomeFunc:
void
SomeFunc(Sample &x)
{
cout <<
"Say i am in someFunc " << endl;
}
because when we pass objects
by refernece that object is not destroyed. while returning from the function.
2)
Which is the parameter that is added to every
non-static member function when it is called?
Answer:
‘this’
pointer
3) class base
{
public:
int bval;
base(){ bval=0;}
};
class deri:public base
{
public:
int dval;
deri(){ dval=1;}
};
void SomeFunc(base *arr,int size)
{
for(int i=0; i<size;
i++,arr++)
cout<<arr->bval;
cout<<endl;
}
int main()
{
base BaseArr[5];
SomeFunc(BaseArr,5);
deri DeriArr[5];
SomeFunc(DeriArr,5);
}
Answer:
00000
01010
Explanation:
The function
SomeFunc expects two arguments.The first one is a pointer to an array of base
class objects and the second one is the sizeof the array.The first call of
someFunc calls it with an array of bae objects, so it works correctly and
prints the bval of all the objects. When Somefunc is called the second time the
argument passed is the pointeer to an array of derived class objects and not
the array of base class objects. But that is what the function expects to be
sent. So the derived class pointer is promoted to base class pointer and the
address is sent to the function. SomeFunc() knows nothing about this and just
treats the pointer as an array of base class objects. So when arr++ is met, the
size of base class object is taken into consideration and is incremented by
sizeof(int) bytes for bval (the deri class objects have bval and dval as
members and so is of size >= sizeof(int)+sizeof(int) ).
4) class base
{
public:
void baseFun(){ cout<<"from
base"<<endl;}
};
class deri:public base
{
public:
void
baseFun(){ cout<< "from derived"<<endl;}
};
void SomeFunc(base *baseObj)
{
baseObj->baseFun();
}
int main()
{
base baseObject;
SomeFunc(&baseObject);
deri deriObject;
SomeFunc(&deriObject);
}
Answer:
from
base
from
base
Explanation:
As
we have seen in the previous case, SomeFunc expects a pointer to a base class.
Since a pointer to a derived class object is passed, it treats the argument
only as a base class pointer and the corresponding base function is called.
5) class base
{
public:
virtual
void baseFun(){ cout<<"from base"<<endl;}
};
class deri:public base
{
public:
void
baseFun(){ cout<< "from derived"<<endl;}
};
void SomeFunc(base *baseObj)
{
baseObj->baseFun();
}
int main()
{
base baseObject;
SomeFunc(&baseObject);
deri deriObject;
SomeFunc(&deriObject);
}
Answer:
from
base
from
derived
Explanation:
Remember
that baseFunc is a virtual function. That means that it supports run-time
polymorphism. So the function corresponding to the derived class object is
called.
void main()
{
int
a, *pa, &ra;
pa
= &a;
ra
= a;
cout
<<"a="<<a <<"*pa="<<*pa
<<"ra"<<ra ;
}
/*
Answer :
Compiler
Error: 'ra',reference must be initialized
Explanation :
Pointers are different from
references. One of the main differences is that the pointers can be both
initialized and assigned, whereas references can only be initialized. So this
code issues an error.
*/
const int size = 5;
void print(int *ptr)
{
cout<<ptr[0];
}
void print(int ptr[size])
{
cout<<ptr[0];
}
void main()
{
int
a[size] = {1,2,3,4,5};
int
*b = new int(size);
print(a);
print(b);
}
/*
Answer:
Compiler
Error : function 'void print(int *)' already has a body
Explanation:
Arrays
cannot be passed to functions, only pointers (for arrays, base addresses)
can be passed. So the arguments int *ptr
and int prt[size] have no difference
as function arguments. In other words,
both the functoins have the same signature and
so cannot be overloaded.
*/
class some{
public:
~some()
{
cout<<"some's
destructor"<<endl;
}
};
void main()
{
some
s;
s.~some();
}
/*
Answer:
some's
destructor
some's
destructor
Explanation:
Destructors
can be called explicitly. Here 's.~some()' explicitly calls the
destructor of 's'. When main() returns,
destructor of s is called again,
hence the result.
*/
#include <iostream.h>
class fig2d
{
int
dim1;
int
dim2;
public:
fig2d()
{ dim1=5; dim2=6;}
virtual
void operator <<(ostream & rhs);
};
void fig2d::operator <<(ostream
&rhs)
{
rhs
<<this->dim1<<" "<<this->dim2<<"
";
}
/*class fig3d : public fig2d
{
int
dim3;
public:
fig3d()
{ dim3=7;}
virtual
void operator <<(ostream &rhs);
};
void fig3d::operator <<(ostream
&rhs)
{
fig2d::operator
<<(rhs);
rhs<<this->dim3;
}
*/
void main()
{
fig2d
obj1;
// fig3d
obj2;
obj1
<< cout;
// obj2
<< cout;
}
/*
Answer :
5
6
Explanation:
In
this program, the << operator is overloaded with ostream as argument.
This enables the 'cout' to be present at
the right-hand-side. Normally, 'cout'
is implemented as global function, but
it doesn't mean that 'cout' is not possible
to be overloaded as member function.
Overloading << as virtual member function becomes handy when the
class in which
it is overloaded is inherited, and this
becomes available to be overrided. This is as opposed
to global friend functions, where
friend's are not inherited.
*/
class opOverload
{
public:
bool
operator==(opOverload temp);
};
bool opOverload::operator==(opOverload
temp){
if(*this == temp ){
cout<<"The
both are same objects\n";
return
true;
}
else{
cout<<"The
both are different\n";
return
false;
}
}
void main(){
opOverload
a1, a2;
a1=
=a2;
}
Answer :
Runtime
Error: Stack Overflow
Explanation :
Just
like normal functions, operator functions can be called recursively. This
program just illustrates that point, by calling the operator == function
recursively, leading to an infinite loop.
class complex{
double
re;
double
im;
public:
complex()
: re(1),im(0.5) {}
bool
operator==(complex &rhs);
operator
int(){}
};
bool complex::operator == (complex
&rhs){
if((this->re
== rhs.re) && (this->im == rhs.im))
return
true;
else
return
false;
}
int main(){
complex c1;
cout<< c1;
}
Answer : Garbage value
Explanation:
The programmer wishes to print the
complex object using output re-direction operator, which he has not defined for
his class. But the compiler instead of giving an error sees the conversion
function and converts the user-defined object to standard object and prints
some garbage value.
class complex
{
double
re;
double
im;
public:
complex()
: re(0),im(0) {}
complex(double
n) { re=n,im=n;};
complex(int
m,int n) { re=m,im=n;}
void
print() { cout<<re; cout<<im;}
};
void main()
{
complex
c3;
double
i=5;
c3
= i;
c3.print();
}
Answer:
5,5
Explanation:
Though no operator= function taking
complex, double is defined, the double on the rhs is converted into a temporary
object using the single argument constructor taking double and assigned to the
lvalue.
void main()
{
int
a, *pa, &ra;
pa
= &a;
ra
= a;
cout
<<"a="<<a <<"*pa="<<*pa
<<"ra"<<ra ;
}
Answer :
Compiler
Error: 'ra',reference must be initialized
Explanation :
Pointers
are different from references. One of the main
differences is that the pointers can be
both initialized and assigned,
whereas references can only be
initialized. So this code issues an error.
Try it Yourself
1) Determine the output of the
'C++' Codelet.
class
base
{
public
:
out()
{
cout<<"base
";
}
};
class
deri{
public
: out()
{
cout<<"deri
";
}
};
void
main()
{
deri dp[3];
base
*bp = (base*)dp;
for
(int i=0; i<3;i++)
(bp++)->out();
}
2)
Justify the use of virtual constructors and destructors
in C++.
3)
Each C++ object possesses the 4 member fns, (which can
be declared by the programmer explicitly or by the implementation if they are
not available). What are those 4 functions?
4)
What is wrong
with this class declaration?
class
something
{
char
*str;
public:
something(){
st = new char[10]; }
~something()
{
delete
str;
}
};
5) Inheritance is also known as
-------- relationship. Containership as
________ relationship.
6) When is it necessary to use
member-wise initialization list (also
known as header initialization list) in C++?
7) Which is the only operator in
C++, which can be overloaded but NOT inherited.
8) Is there anything wrong with
this C++ class declaration?
class
temp
{
int value1;
mutable int value2;
public :
void
fun(int val)
const{
((temp*)
this)->value1 = 10;
value2
= 10;
}
};
1. What is a modifier?
Answer:
A modifier, also called a modifying
function is a member function that changes the value of at least one data
member. In other words, an operation that modifies the state of an object.
Modifiers are also known as ‘mutators’.
2. What is an accessor?
Answer:
An accessor is a class operation that
does not modify the state of an object. The accessor functions need to be
declared as const operations
3. Differentiate between a
template class and class template.
Answer:
Template class:
A generic
definition or a parameterized class not instantiated until the client provides
the needed information. It’s jargon for plain templates.
Class template:
A class template
specifies how individual classes can be constructed much like the way a class
specifies how individual objects can be constructed. It’s jargon for plain
classes.
4. When does a name clash
occur?
Answer:
A
name clash occurs when a name is
defined in more than one place. For example., two different class libraries
could give two different classes the same name. If you try to use many class
libraries at the same time, there is a fair chance that you will be unable to
compile or link the program because of name clashes.
5. Define namespace.
Answer:
It
is a feature in c++ to minimize name collisions in the global name space. This
namespace keyword assigns a distinct name to a library that allows other
libraries to use the same identifier names without creating any name
collisions. Furthermore, the compiler uses the namespace signature for
differentiating the definitions.
6. What is the use of ‘using’
declaration.
Answer:
A
using declaration makes it possible to use a name from a namespace without the
scope operator.
7. What is an Iterator class?
Answer:
A
class that is used to traverse through the objects maintained by a container
class. There are five categories of iterators:
Ø
input
iterators,
Ø
output iterators,
Ø
forward iterators,
Ø
bidirectional iterators,
Ø
random
access.
An iterator is
an entity that gives access to the contents of a container object without
violating encapsulation constraints. Access to the contents is granted on a
one-at-a-time basis in order. The order can be storage order (as in lists and
queues) or some arbitrary order (as in array indices) or according to some
ordering relation (as in an ordered binary tree). The iterator is a construct,
which provides an interface that, when called, yields either the next element
in the container, or some value denoting the fact that there are no more elements
to examine. Iterators hide the details of access to and update of the elements
of a container class.
The simplest and
safest iterators are those that permit read-only access to the contents of a
container class. The following code fragment shows how an iterator might appear
in code:
cont_iter:=new cont_iterator();
x:=cont_iter.next();
while x/=none do
...
s(x);
...
x:=cont_iter.next();
end;
In this example, cont_iter is the name
of the iterator. It is created on the first line by instantiation of
cont_iterator class, an iterator class defined to iterate over some container
class, cont. Succesive elements from the container are carried to x. The loop
terminates when x is bound to some empty value. (Here, none)In the middle of
the loop, there is s(x) an operation on x, the current element from the
container. The next element of the container is obtained at the bottom of the
loop.
9. List out some of the OODBMS
available.
Answer:
Ø
GEMSTONE/OPAL of Gemstone systems.
Ø
ONTOS
of Ontos.
Ø
Objectivity of Objectivity inc.
Ø
Versant of Versant object technology.
Ø
Object store of Object Design.
Ø
ARDENT of ARDENT software.
Ø
POET of POET software.
10. List out some of the
object-oriented methodologies.
Answer:
Ø
Object Oriented Development (OOD) (Booch 1991,1994).
Ø
Object Oriented Analysis and Design (OOA/D) (Coad and Yourdon 1991).
Ø
Object Modelling Techniques (OMT)
(Rumbaugh 1991).
Ø
Object Oriented Software Engineering (Objectory) (Jacobson 1992).
Ø
Object Oriented Analysis (OOA) (Shlaer and Mellor 1992).
Ø
The
Fusion Method (Coleman 1991).
11. What is an incomplete type?
Answer:
Incomplete
types refers to pointers in which there is non availability of the
implementation of the referenced location or it points to some location whose
value is not available for modification.
Example:
int *i=0x400 // i points to address 400
*i=0; //set the value of memory location
pointed by i.
Incomplete types are otherwise
called uninitialized pointers.
12. What is a dangling pointer?
Answer:
A dangling
pointer arises when you use the address of an object after its lifetime is
over.
This may occur in situations like
returning addresses of the automatic variables from a function or using the
address of the memory block after it is freed.
13. Differentiate between the
message and method.
Answer:
Message
Method
Objects communicate by sending
messages Provides response to a
message.
to each other.
A message is sent to invoke a
method. It is an
implementation of an operation.
14. What is an adaptor class or
Wrapper class?
Answer:
A class that has
no functionality of its own. Its member functions hide the use of a third party
software component or an object with the non-compatible interface or a non-
object- oriented implementation.
15. What is a Null object?
Answer:
It is an object
of some class whose purpose is to indicate that a real object of that class
does not exist. One common use for a null object is a return value from a
member function that is supposed to return an object with some specified
properties but cannot find such an object.
16. What is class invariant?
Answer:
A class
invariant is a condition that defines all valid states for an object. It is a
logical condition to ensure the correct working of a class. Class invariants
must hold when an object is created, and they must be preserved under all
operations of the class. In particular all class invariants are both
preconditions and post-conditions for all operations or member functions of the
class.
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