Q:
Is it possible to have Virtual Constructor? If yes, how? If not, Why not
possible?
A:
There is nothing like Virtual Constructor. The Constructor can’t be virtual
as the constructor
is a
code which is responsible for creating an instance of a class and it can’t be
delegated to
any
other object by virtual keyword means.
Q:
What is constructor ?
A:
Constructor creates an object and initializes it. It also creates vtable
for virtual functions. It is
different
from other methods in a class.
Q:
What about Virtual Destructor?
A:
Yes there is a Virtual Destructor. A destructor can be virtual as it is
possible as at runtime
depending
on the type of object caller is calling to, proper destructor will be called.
Q:
What is the difference between a copy constructor and an overloaded
assignment operator?
A:
A copy constructor constructs a new object by using the content of the
argument object. An
overloaded
assignment operator assigns the contents of an existing object to another
existing
object
of the same class.
Q:
Can a constructor throws an exception? How to handle the error when the
constructor fails?
A:The
constructor never throws an error.
Q:
What is default constructor?
A:
Constructor with no arguments or all the arguments has default values.
Q:
What is copy constructor?
A:
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:
(a)
Boo Obj1(10); // calling Boo constructor
(b)
Boo Obj2(Obj1); // calling boo copy constructor
(c)
Boo Obj2 = Obj1;// calling boo copy constructor
Q:
When are copy constructors called?
A:
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
Q:
Can a copy constructor accept an object of the same class as parameter,
instead of reference
of
the object?
A:
No. It is specified in the definition of the copy constructor itself. It
should generate an error if
a
programmer specifies a copy constructor with a first argument that is an object
and not a
reference.
Q:
What is conversion constructor?
A:
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
Q:What
is conversion operator??
A: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.
Q:
How can I handle a constructor that fails?
A:
throw an exception. Constructors don't have a return type, so it's not
possible to use return
codes.
The best way to signal constructor failure is therefore to throw an exception.
Q:
How can I handle a destructor that fails?
A: Write a message to a log-fille. But do not throw an exception. The C++ rule is that you must never throw an exception from a destructor that is being called during the "stack unwinding" process of another exception. For example, if someone says throw Foo(), the stack will be unwound so all the stack frames between the throw Foo() and the } catch (Foo e) { will get popped. This is called stack unwinding. During stack unwinding, all the local objects in all those stack frames are destructed. If one of those destructors throws an exception (say it throws a Bar object), the C++ runtime system is in a no-win situation: should it ignore the Bar and end up in the } catch (Foo e) { where it was originally headed? Should it ignore the Foo and look for a } catch (Bare) { handler? There is no good answer:either choice loses information. So the C++ language guarantees that it will call terminate() at this point, and terminate() kills the process. Bang you're dead.
Q:
What is Virtual Destructor?
A:
Using virtual destructors, you can destroy objects without knowing their
type - the correct
destructor for the object is invoked using the virtual function mechanism. Note that destructors can also be declared as pure virtual functions for abstract classes. if someone will derive from your class, and if someone will say "new Derived", where "Derived" is derived from your class, and if someone will say delete p, where the actual object's type is "Derived" but the pointer p's type is your class.
Q: Can a copy constructor accept an object of the same class as parameter, instead of reference of the object?
A: No. It is specified in the definition of the copy constructor itself. It should generate an error if a programmer specifies a copy constructor with a first argument that is an object and not a reference.
Q:
What's the order that local objects are destructed?
A:
In reverse order of construction: First constructed, last destructed.
In
the following example, b's destructor will be executed first, then a's
destructor:
void
userCode()
{
Fred
a;
Fred
b;
...
}
Q:
What's the order that objects in an array are destructed?
A:
In reverse order of construction: First constructed, last destructed.
In
the following example, the order for destructors will be a[9], a[8], ..., a[1],
a[0]:
void
userCode()
{
Fred
a[10];
...
}
Q:
Can I overload the destructor for my class?
A:
No.
You can
have only one destructor for a class Fred. It's always called Fred::~Fred(). It
never takes
any
parameters, and it never returns anything.
You can't pass parameters to the destructor anyway, since you never explicitly call a destructor (well, almost never).
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