Interview : C++ Interview Questions (Page - 1)
What
is encapsulation??
Containing and
hiding information about an object, such as internal data structures and code.
Encapsulation isolates the internal complexity of an object's operation from the
rest of the application. For example, a client component asking for net revenue
from a business object need not know the data's origin.
What is inheritance?
Inheritance allows one class to reuse the state and behavior of another
class. The derived class inherits the properties and method implementations of
the base class and extends it by overriding methods and adding additional
properties and methods.
What is Polymorphism??
Polymorphism allows a client to treat different objects in the same way even if
they were created from different classes and exhibit different behaviors. You
can use implementation inheritance to achieve polymorphism in languages such as
C++ and Java. Base class object's pointer can invoke methods in derived class
objects. You can also achieve polymorphism in C++ by function overloading and
operator overloading.
What is constructor or Actor?
Constructor creates an object and initializes it. It also creates vtable for
virtual functions. It is different from other methods in a class.
What
is destructor?
Destructor usually
deletes any extra resources allocated by the object.
What
is default constructor?
Constructor with
no arguments or all the arguments has default values.
What
is copy constructor?
Constructor which
initializes the it's object member variables ( by shallow copying) with another
object of the same class. If you don't implement one in your class then compiler
implements one for you.
for example:
Boo Obj1(10); // calling Boo constructor
Boo Obj2(Obj1); // calling boo copy constructor
Boo Obj2 = Obj1;// calling boo copy constructor
When
are copy constructors called?
Copy
constructors are called in following cases:
a) when a function returns an object of that class by value
b) when the object of that class is passed by value as an argument to a function
c) when you construct an object based on another object of the same class
d) When compiler generates a temporary object
What
is assignment operator?
Default assignment
operator handles assigning one object to another of the same class. Member to
member copy (shallow copy)
What
are all the implicit member functions of the class? Or what are all the
functions which compiler implements for us if we don't define one.?
default ctor
copy ctor
assignment operator
default destructor
address operator
What
is conversion constructor?
constructor with a
single argument makes that constructor as conversion ctor and it can be
used for type conversion.
for example:
class Boo
{
public:
Boo( int i );
};
Boo BooObject = 10 ; // assigning int 10 Boo object
What
is conversion operator?
class can have a
public method for specific data type conversions.
for example:
class Boo
{
double value;
public:
Boo(int i )
operator double()
{
return value;
}
};
Boo BooObject;
double i = BooObject; // assigning object to variable i of type double. now
conversion operator gets called to assign the value.
What
is diff between malloc()/free() and new/delete?
malloc allocates
memory for object in heap but doesn't invoke object's constructor to initiallize
the object.
new allocates memory and also invokes constructor to initialize the object.
malloc() and free() do not support object semantics Does not construct and
destruct objects
string * ptr = (string *)(malloc (sizeof(string)))
Are not safe
Does not calculate the size of the objects that it construct
Returns a pointer to void
int *p = (int *) (malloc(sizeof(int)));
int *p = new int;
Are not extensible
new and delete can be overloaded in a class
"delete" first calls the object's termination routine (i.e. its
destructor) and then
releases the space the object occupied on the heap memory. If an array of
objects was
created using new, then delete must be told that it is dealing with an array by
preceding
the name with an empty []:-
Int_t *my_ints = new Int_t[10];
...
delete []my_ints;
What is the diff between "new" and "operator new" ?
"operator new" works like malloc.
What is difference between template and macro?
There is no way for the compiler to verify that the macro parameters are of
compatible
types. The macro is expanded without any special type checking. If macro
parameter has a postincremented variable ( like c++ ), the increment is
performed two times. Because macros are expanded by the preprocessor, compiler
error messages will refer to the expanded macro, rather than the macro
definition itself. Also, the macro will show up in expanded form during
debugging.
for example:
Macro:
#define min(i, j) (i < j ? i : j)
template:
template<class T>
T min (T i, T j)
{
return i < j ? i : j;
}
What are C++ storage classes?
auto
register
static
extern
auto: the default. Variables are automatically created and initialized
when they are defined and are destroyed at the end of the block containing their
definition. They are not visible outside that block
register: a type of auto variable. a suggestion to the compiler to use a
CPU register for performance
static: a variable that is known only in the function that contains its
definition but is never destroyed and retains its value between calls to that
function. It exists from the time the program begins execution
extern: a static variable whose definition and placement is determined
when all object and library modules are combined (linked) to form the executable
code file. It can be visible outside the file where it is defined.
