C++ Questions
Note : All the programs are tested under Turbo C++
3.0, 4.5 and Microsoft VC++ 6.0 compilers.
It is assumed that,
Ø Programs run under Windows environment,
Ø The underlying machine is an x86 based system,
Ø Program is compiled using Turbo C/C++ compiler.
The program output may depend on the information based on this
assumptions (for example sizeof(int) == 2 may be assumed).
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 lass.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.
17. What do
you mean by Stack unwinding?
Answer:
It is a process during exception handling when the destructor is
called for all local objects between the place where the exception was thrown
and where it is caught.
18. Define
precondition and post-condition to a member function.
Answer:
Precondition:
A precondition is a condition that must be true on entry to a member
function. A class is used correctly if preconditions are never false. An
operation is not responsible for doing anything sensible if its precondition
fails to hold.
For example, the interface invariants of stack class say nothing about pushing yet another element on a
stack that is already full. We say that isful()
is a precondition of the push
operation.
Post-condition:
A post-condition is a condition that must be true on exit from a
member function if the precondition was valid on entry to that function. A
class is implemented correctly if post-conditions are never false.
For example, after pushing an element on the stack, we know that isempty() must necessarily hold. This is
a post-condition of the push
operation.
19. What are
the conditions that have to be met for a condition to be an invariant of the
class?
Answer:
Ø The condition should hold at the end of every constructor.
Ø The condition should hold at the end of every mutator(non-const)
operation.
20. What are
proxy objects?
Answer:
Objects that stand for other objects are called proxy objects or
surrogates.
Example:
template<class T>
class Array2D
{
public:
class Array1D
{
public:
T&
operator[] (int index);
const T&
operator[] (int index) const;
...
};
Array1D
operator[] (int index);
const Array1D
operator[] (int index) const;
...
};
The following then becomes legal:
Array2D<float>data(10,20);
........
cout<<data[3][6]; // fine
Here
data[3] yields an Array1D object and the operator [] invocation on that object
yields the float in position(3,6) of the original two dimensional array.
Clients of the Array2D class need not be aware of the presence of the Array1D
class. Objects of this latter class stand for one-dimensional array objects
that, conceptually, do not exist for clients of Array2D. Such clients program
as if they were using real, live, two-dimensional arrays. Each Array1D object
stands for a one-dimensional array that is absent from a conceptual model used
by the clients of Array2D. In the above example, Array1D is a proxy class. Its
instances stand for one-dimensional arrays that, conceptually, do not exist.
21. Name some
pure object oriented languages.
Answer:
Ø Smalltalk,
Ø Java,
Ø Eiffel,
Ø Sather.
22. Name the
operators that cannot be overloaded.
Answer:
sizeof . .* .-> :: ?:
23. What is a
node class?
Answer:
A node class is a class that,
Ø relies on the base class for services and implementation,
Ø provides a wider interface to te users than its base class,
Ø relies primarily on virtual functions in its public interface
Ø depends on all its direct and indirect base class
Ø can be understood only in the context of the base class
Ø can be used as base for further derivation
Ø can be used to create objects.
A node class is
a class that has added new services or functionality beyond the services
inherited from its base class.
24. What is an orthogonal base class?
Answer:
If two base classes have no overlapping methods or data they are
said to be independent of, or orthogonal to each other. Orthogonal in the sense
means that two classes operate in different dimensions and do not interfere
with each other in any way. The same derived class may inherit such classes
with no difficulty.
25. What is a container
class? What are the types of container classes?
Answer:
A container class is a class that is used to hold objects in memory
or external storage. A container class acts as a generic holder. A container
class has a predefined behavior and a well-known interface. A container class
is a supporting class whose purpose is to hide the topology used for
maintaining the list of objects in memory. When a container class contains a
group of mixed objects, the container is called a heterogeneous container; when
the container is holding a group of objects that are all the same, the
container is called a homogeneous container.
26. What is a protocol
class?
Answer:
An abstract class is a protocol class if:
Ø it neither contains nor inherits from classes that contain member
data, non-virtual functions, or private (or protected) members of any kind.
Ø it has a non-inline virtual destructor defined with an empty
implementation,
Ø all member functions other than the destructor including inherited
functions, are declared pure virtual functions and left undefined.
27. What is a mixin class?
Answer:
A class that provides some but not all of the implementation for a
virtual base class is often called mixin. Derivation done just for the purpose
of redefining the virtual functions in the base classes is often called mixin
inheritance. Mixin classes typically don't share common bases.
28. What is a concrete
class?
Answer:
A concrete class is used to define a useful object that can be
instantiated as an automatic variable on the program stack. The implementation
of a concrete class is defined. The concrete class is not intended to be a base
class and no attempt to minimize dependency on other classes in the implementation
or behavior of the class.
29.What is the handle
class?
Answer:
A handle is a class that maintains a pointer to an object that is
programmatically accessible through the public interface of the handle class.
Explanation:
In
case of abstract classes, unless one manipulates the objects of these classes
through pointers and references, the benefits of the virtual functions are
lost. User code may become dependent on details of implementation classes
because an abstract type cannot be allocated statistically or on the stack
without its size being known. Using pointers or references implies that the
burden of memory management falls on the user. Another limitation of abstract
class object is of fixed size. Classes however are used to represent concepts that
require varying amounts of storage to implement them.
A popular
technique for dealing with these issues is to separate what is used as a single
object in two parts: a handle providing the user interface and a representation
holding all or most of the object's state. The connection between the handle
and the representation is typically a pointer in the handle. Often, handles
have a bit more data than the simple representation pointer, but not much more.
Hence the layout of the handle is typically stable, even when the
representation changes and also that handles are small enough to move around
relatively freely so that the user needn’t use the pointers and the
references.
30. What is an action class?
Answer:
The simplest and most obvious way to specify an action in C++ is to
write a function. However, if the action has to be delayed, has to be
transmitted 'elsewhere' before being performed, requires its own data, has to
be combined with other actions, etc then it often becomes attractive to provide
the action in the form of a class that can execute the desired action and
provide other services as well. Manipulators used with iostreams is an obvious
example.
Explanation:
A common form of
action class is a simple class containing just one virtual function.
class Action
{
public:
virtual
int do_it( int )=0;
virtual
~Action( );
}
Given this, we can write code say a member that can store actions
for later execution without using pointers to functions, without knowing
anything about the objects involved, and without even knowing the name of the
operation it invokes. For example:
class write_file : public Action
{
File& f;
public:
int do_it(int)
{
return
fwrite( ).suceed( );
}
};
class error_message:
public Action
{
response_box
db(message.cstr( ),"Continue","Cancel","Retry");
switch (db.getresponse( ))
{
case
0: return 0;
case
1: abort();
case
2: current_operation.redo( );return 1;
}
};
A user
of the Action class will be completely isolated from any knowledge of derived
classes such as write_file and error_message.
31. When can you tell that
a memory leak will occur?
Answer:
A memory leak occurs when a program loses the ability to free a
block of dynamically allocated memory.
32.What is a parameterized
type?
Answer:
A template is a parameterized construct or type containing generic
code that can use or manipulate any type. It is called parameterized because an
actual type is a parameter of the code body. Polymorphism may be achieved
through parameterized types. This type of polymorphism is called parameteric
polymorphism. Parameteric polymorphism is the mechanism by which the same code
is used on different types passed as parameters.
33. Differentiate between a
deep copy and a shallow copy?
Answer:
Deep copy involves using the contents of one object to create
another instance of the same class. In a deep copy, the two objects may contain
ht same information but the target object will have its own buffers and resources.
the destruction of either object will not affect the remaining object. The
overloaded assignment operator would create a deep copy of objects.
Shallow copy involves copying the contents of one object into
another instance of the same class thus creating a mirror image. Owing to
straight copying of references and pointers, the two objects will share the
same externally contained contents of the other object to be unpredictable.
Explanation:
Using a copy constructor we simply copy the data values member by
member. This method of copying is called shallow copy. If the object is a
simple class, comprised of built in types and no pointers this would be
acceptable. This function would use the values and the objects and its behavior
would not be altered with a shallow copy, only the addresses of pointers that
are members are copied and not the value the address is pointing to. The data
values of the object would then be inadvertently altered by the function. When
the function goes out of scope, the copy of the object with all its data is
popped off the stack.
If the object has any pointers a deep copy needs to be executed.
With the deep copy of an object, memory is allocated for the object in free
store and the elements pointed to are copied. A deep copy is used for objects
that are returned from a function.
34. What is an opaque
pointer?
Answer:
A pointer is said to be opaque if the definition of the type to
which it points to is not included in the current translation unit. A
translation unit is the result of merging an implementation file with all its
headers and header files.
35. What is a smart
pointer?
Answer:
A smart pointer is an object that acts, looks and feels like a
normal pointer but offers more functionality. In C++, smart pointers are
implemented as template classes that
encapsulate a pointer and override standard pointer operators. They have a
number of advantages over regular pointers. They are guaranteed to be
initialized as either null pointers or pointers to a heap object. Indirection
through a null pointer is checked. No delete is ever necessary. Objects are
automatically freed when the last pointer to them has gone away. One
significant problem with these smart pointers is that unlike regular pointers,
they don't respect inheritance. Smart pointers are unattractive for polymorphic
code. Given below is an example for the implementation of smart pointers.
Example:
template <class X>
class smart_pointer
{
public:
smart_pointer();
// makes a null pointer
smart_pointer(const X& x)
// makes pointer to copy of x
X&
operator *( );
const
X& operator*( ) const;
X*
operator->() const;
smart_pointer(const smart_pointer
<X> &);
const
smart_pointer <X> & operator =(const smart_pointer<X>&);
~smart_pointer();
private:
//...
};
This class implement a smart pointer to an object of type X. The
object itself is located on the heap. Here is how to use it:
smart_pointer
<employee> p= employee("Harris",1333);
Like other overloaded operators, p will behave like a regular
pointer,
cout<<*p;
p->raise_salary(0.5);
36. What is reflexive
association?
Answer:
The 'is-a' is called a reflexive association because the reflexive
association permits classes to bear the is-a association not only with their
super-classes but also with themselves. It differs from a 'specializes-from'
as 'specializes-from' is usually used to
describe the association between a super-class and a sub-class. For example:
Printer is-a printer.
37. What is slicing?
Answer:
Slicing means that the data added by a subclass are discarded when an
object of the subclass is passed or returned by value or from a function
expecting a base class object.
Explanation:
Consider the following class declaration:
class base
{
...
base&
operator =(const base&);
base
(const base&);
}
void fun( )
{
base e=m;
e=m;
}
As base copy functions don't know anything about the derived only
the base part of the derived is copied. This is commonly referred to as
slicing. One reason to pass objects of classes in a hierarchy is to avoid
slicing. Other reasons are to preserve polymorphic behavior and to gain
efficiency.
38. What is name mangling?
Answer:
Name mangling is the process through which your c++ compilers give
each function in your program a unique name. In C++, all programs have at-least
a few functions with the same name. Name mangling is a concession to the fact
that linker always insists on all function names being unique.
Example:
In general, member
names are made unique by concatenating the name of the member with that of the
class e.g. given the declaration:
class Bar
{
public:
int ival;
...
};
ival becomes something like:
// a possible member
name mangling
ival__3Bar
Consider this derivation:
class Foo : public Bar
{
public:
int ival;
...
}
The internal representation of a Foo object is the concatenation of
its base and derived class members.
// Pseudo C++ code
// Internal representation
of Foo
class Foo
{
public:
int ival__3Bar;
int ival__3Foo;
...
};
Unambiguous access of either ival members is achieved through name
mangling. Member functions, because they can be overloaded, require an
extensive mangling to provide each with a unique name. Here the compiler
generates the same name for the two overloaded instances(Their argument lists
make their instances unique).
39. What are proxy objects?
Answer:
Objects that points to other objects are called proxy objects or
surrogates. Its an object that provides the same interface as its server object
but does not have any functionality. During a method invocation, it routes data
to the true server object and sends back the return value to the object.
40. Differentiate between
declaration and definition in C++.
Answer:
A declaration introduces a name into the program; a definition
provides a unique description of an entity (e.g. type, instance, and function).
Declarations can be repeated in a given scope, it introduces a name in a given
scope. There must be exactly one definition of every object, function or class
used in a C++ program.
A declaration is a definition unless:
Ø it declares a function without specifying its body,
Ø it contains an extern specifier and no initializer or function body,
Ø it is the declaration of a static class data member without a class
definition,
Ø it is a class name definition,
Ø it is a typedef declaration.
A definition is a
declaration unless:
Ø it defines a static class data member,
Ø it defines a non-inline member function.
41. What is cloning?
Answer:
An object can carry
out copying in two ways i.e. it can set itself to be a copy of another object,
or it can return a copy of itself. The latter process is called cloning.
42. Describe the main
characteristics of static functions.
Answer:
The main
characteristics of static functions include,
Ø It is without the a this pointer,
Ø It can't directly access the non-static members of its class
Ø It can't be declared const, volatile or virtual.
Ø It doesn't need to be invoked through an object of its class,
although for convenience, it may.
43. Will the inline
function be compiled as the inline function always? Justify.
Answer:
An inline function
is a request and not a command. Hence it won't be compiled as an inline
function always.
Explanation:
Inline-expansion
could fail if the inline function contains loops, the address of an inline
function is used, or an inline function is called in a complex expression. The
rules for inlining are compiler dependent.
44. Define a way other than
using the keyword inline to make a function inline.
Answer:
The function must
be defined inside the class.
45. How can a '::' operator
be used as unary operator?
Answer:
The scope operator can be
used to refer to members of the global namespace. Because the global namespace
doesn’t have a name, the notation :: member-name refers to a member of the
global namespace. This can be useful for referring to members of global
namespace whose names have been hidden by names declared in nested local scope.
Unless we specify to the compiler in which namespace to search for a declaration,
the compiler simple searches the current scope, and any scopes in which the
current scope is nested, to find the declaration for the name.
46. What is placement new?
Answer:
When you want to
call a constructor directly, you use the placement new. Sometimes you have some
raw memory that's already been allocated, and you need to construct an object
in the memory you have. Operator new's special version placement new allows you
to do it.
class Widget
{
public :
Widget(int widgetsize);
...
Widget*
Construct_widget_int_buffer(void *buffer,int widgetsize)
{
return new(buffer) Widget(widgetsize);
}
};
This function
returns a pointer to a Widget object that's constructed within the buffer
passed to the function. Such a function might be useful for applications using
shared memory or memory-mapped I/O, because objects in such applications must
be placed at specific addresses or in memory allocated by special routines.
OOAD
1.
What do you mean by analysis and design?
Analysis:
Basically, it is the
process of determining what needs to be done before how it should be done. In
order to accomplish this, the developer refers the existing systems and
documents. So, simply it is an art of discovery.
Design:
It is the process of
adopting/choosing the one among the many, which best accomplishes the users
needs. So, simply, it is compromising mechanism.
2.
What are the steps involved in designing?
Before getting into the
design the designer should go through the SRS prepared by the System Analyst.
The
main tasks of design are Architectural Design and Detailed Design.
In
Architectural Design we find what are the main modules in the problem domain.
In Detailed Design we find
what should be done within each module.
3.
What are the main underlying concepts of object orientation?
Objects, messages, class,
inheritance and polymorphism are the main concepts of object orientation.
4.
What do u meant by "SBI" of an object?
SBI stands for State,
Behavior and Identity. Since every object has the above three.
Ø State:
It
is just a value to the attribute of an object at a particular time.
Ø Behaviour:
It
describes the actions and their reactions of that object.
Ø Identity:
An object has an identity
that characterizes its own existence. The identity makes it possible to
distinguish any object in an unambiguous way, and independently from its state.
5.
Differentiate persistent & non-persistent objects?
Persistent refers to an
object's ability to transcend time or space. A persistent object stores/saves
its state in a permanent storage system with out losing the information
represented by the object.
A non-persistent object is
said to be transient or ephemeral. By default objects are considered as
non-persistent.
6.
What do you meant by active and passive objects?
Active objects are one
which instigate an interaction which owns a thread and they are responsible for
handling control to other objects. In simple words it can be referred as client.
Passive objects are one,
which passively waits for the message to be processed. It waits for another
object that requires its services. In simple words it can be referred as server.
Diagram:
client server
(Active) (Passive)
7.
What is meant by software development method?
Software development
method describes how to model and build software systems in a reliable and
reproducible way. To put it simple, methods that are used to represent ones'
thinking using graphical notations.
8.
What are models and meta models?
Model:
It is a complete description of something (i.e.
system).
Meta model:
It describes the model
elements, syntax and semantics of the notation that allows their manipulation.
9.
What do you meant by static and dynamic modeling?
Static modeling is used to
specify structure of the objects that exist in the problem domain. These are
expressed using class, object and USECASE diagrams.
But Dynamic modeling
refers representing the object interactions during runtime. It is represented
by sequence, activity, collaboration and
statechart diagrams.
10.
How to represent the interaction between the modeling elements?
Model
element is just a notation to represent (Graphically) the entities that
exist in the problem domain. e.g. for modeling element is class notation,
object notation etc.
Relationships are used to represent the
interaction between the modeling elements.
The following are the Relationships.
Ø Association: Its'
just a semantic connection two classes.
e.g.:
Ø Aggregation: Its'
the relationship between two classes which are related in the fashion that master and slave. The master takes full
rights than the slave. Since the slave works under the master. It is
represented as line with diamond in the master area.
ex:
car contains wheels, etc.
car
Ø Containment: This
relationship is applied when the part contained with in the whole part, dies
when the whole part dies.
It is represented as darked diamond at the
whole part.
example:
class
A{
//some code
};
class B
{
A
aa; // an object of class A;
//
some code for class B;
};
In the above example we see that an object of
class A is instantiated with in the class
B. so the object class A dies when the object class B dies.we can
represnt it in diagram like this.
Ø Generalization: This
relationship used when we want represents a class, which captures the common
states of objects of different classes. It is represented as arrow line pointed
at the class, which has captured the common states.
Ø Dependency: It
is the relationship between dependent and independent classes. Any change in
the independent class will affect the states of the dependent class.
DIAGRAM:
class
A class B
11.
Why generalization is very strong?
Even though Generalization satisfies Structural,
Interface, Behaviour properties. It is mathematically very strong, as it is
Antisymmetric and Transitive.
Antisymmetric:
employee is a person, but not all persons are employees. Mathematically all
As’ are B, but all Bs’ not A.
Transitive: A=>B, B=>c
then A=>c.
A. Salesman.
B. Employee.
C. Person.
Note: All
the other relationships satisfy all the properties like Structural properties,
Interface properties, Behaviour properties.
12.
Differentiate Aggregation and
containment?
Aggregation
is the relationship between the whole and a part. We can add/subtract some properties in the part (slave) side. It won't
affect the whole part.
Best
example is Car, which contains the wheels and some extra parts. Even though the
parts are not there we can call it as car.
But,
in the case of containment the whole part is affected when the part within that
got affected. The human body is an apt example for this relationship. When the
whole body dies the parts (heart etc) are died.
13.
Can link and Association applied
interchangeably?
No,
You cannot apply the link and Association interchangeably. Since link is used
represent the relationship between the two objects.
But
Association is used represent the relationship between the two classes.
link
:: student:Abhilash course:MCA
Association:: student course
14.
what is meant by
"method-wars"?
Before 1994 there were
different methodologies like Rumbaugh, Booch, Jacobson, Meyer etc who followed
their own notations to model the systems. The developers were in a dilemma to
choose the method which best accomplishes their needs. This particular span was called as
"method-wars"
15.
Whether unified method and unified
modeling language are same or different?
Unified method is convergence of the
Rumbaugh and Booch.
Unified modeling lang. is the fusion of
Rumbaugh, Booch and Jacobson as well as Betrand Meyer (whose contribution is
"sequence diagram"). Its' the superset of all the methodologies.
16.
Who were the three famous amigos and
what was their contribution to the
object community?
The Three amigos namely,
Ø James Rumbaugh (OMT): A veteran in analysis who came up with an idea about the objects and their Relationships (in particular
Associations).
Ø Grady Booch: A
veteran in design who came up with an idea about partitioning of systems into
subsystems.
Ø Ivar Jacobson (Objectory): The father of USECASES, who described about the user and system
interaction.
17.
Differentiate the class representation
of Booch, Rumbaugh and UML?
If you look at the class
representaiton of Rumbaugh and UML, It is some what similar and both are very
easy to draw.
Representation:
OMT UML.
Diagram:
Booch:
In this method classes are represented as "Clouds" which are not very
easy to draw as for as the developer's view is concern.
Diagram:
18.
What is an USECASE? Why it is needed?
A
Use Case is a description of a set of sequence of actions that a system
performs that yields an observable result of value to a particular action.
In SSAD process <=> In OOAD
USECASE. It is represented elliptically.
Representation:
19.
Who is an Actor?
An
Actor is someone or something that must interact with the system.In addition to
that an Actor initiates the process(that
is USECASE).
It
is represented as a stickman like this.
Diagram:
 |
20.
What is guard condition?
Guard
condition is one, which acts as a firewall. The access from a particular object
can be made only when the particular condition is met.
For
Example,
customer check customer number ATM.
Here the object on the customer
accesses the ATM facility only when the guard condition is met.
21.
Differentiate the following notations?
I: :obj1 :obj2
II: :obj1 :obj2
In
the above representation I, obj1 sends message to obj2. But in the case of II
the data is transferred from obj1 to obj2.
22.
USECASE is an implementation
independent notation. How will the designer give the implementation details of
a particular USECASE to the programmer?
This can be accomplished
by specifying the relationship called "refinement” which talks about the two different
abstraction of the same thing.
Or
example,
calculate
pay calculate
class1 class2 class3
23.
Suppose a class acts an Actor in the
problem domain, how to represent it in the static model?
In
this scenario you can use “stereotype”. Since stereotype is just a string that
gives extra semantic to the particular entity/model element. It is given with
in the << >>.
class
A
<<
Actor>>
attributes
methods.
24.
Why does the function arguments are
called as "signatures"?
The
arguments distinguish functions with the same name (functional polymorphism).
The name alone does not necessarily identify a unique function. However, the name and its arguments
(signatures) will uniquely identify a function.
In
real life we see suppose, in class there are two guys with same name, but they
can be easily identified by their signatures.
The same concept is applied here.
ex:
class
person
{
public:
char
getsex();
void
setsex(char);
void
setsex(int);
};
In
the above example we see that there is a function setsex() with same name but
with different signature.
No comments:
Post a Comment