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Question:
What is C++? |
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Answer:
C++ is a programming language. It
means "C with Classes", reflecting its
nature as an evolution of the C
language. |
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Question:
Is it possible to have Virtual
Constructor? If yes, how? If not, Why
not possible ? |
Answer:
Virtual Constructor doesn't exist.
Constructor can’t be virtual as
the constructor is a code which is
responsible for creating a instance of
a class and it can’t be delegated to
any other object by virtual keyword
means. |
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Question: Is it
necessary to already know another
programming language before learning
C++? |
Answer:
Not necessarily. C++ is a simple and
clear language in its expressions. It
is true that a piece of code written
with C++ may be seen by a stranger of
programming a bit more cryptic than
some other languages due to the
intensive use of special characters
({}[]*&!|...), but once one knows the
meaning of such characters it can be
even more schematic and clear than
other languages that rely more on
English words.
Also, the simplification of the
input/output interface of C++ in
comparison to C and the incorporation
of the standard template library in
the language, makes the communication
and manipulation of data in a program
written in C++ as simple as in other
languages, without losing the power it
offers. |
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Question: How can I
learn C++? |
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Answer:
There are many ways. Depending on the
time you have and your preferences.
The language is taught in many types
of academic forms throughout the
world, and can also be learnt by
oneself with the help of tutorials and
books. The documentation section of
this Website contains an online
tutorial to help you achieve the
objective of learning this language. |
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Question: What is
Visual C++? And what does "visual
programming" mean? |
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Answer:
Visual C++
is the name of a C++ compiler with an
integrated environment from Microsoft.
It includes special tools that
simplify the development of large
applications as well as specific
libraries that improve productivity.
The use of these tools is generally
known as visual programming. Other
manufacturers also develop these types
of tools and libraries, like Borland
C++, Visual Age, etc... |
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Question:
What about Virtual Destructor? |
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Answer:
Yes there is a Virtual Destructor. A
destructor can be virtual as it is
possible as at runtime depending on
the type of object pointer is pointing
to , proper destructor will be called. |
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Question:
What is Pure Virtual Function? Why and
when it is used ? |
Answer:
The
abstract class whose pure virtual
method has to be implemented by all
the classes which derive on these.
Otherwise it would result in a
compilation error.
This construct should be used when one
wants to ensure that all the derived
classes implement the method defined
as pure virtual in base class. |
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Question:
What is problem with Runtime type
identification? |
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Answer:
The run
time type identification comes at a
cost of performance penalty. Compiler
maintains the class. |
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Question:
How Virtual functions call up is
maintained? |
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Answer:
Through
Look up tables added by the compile to
every class image. This also leads to
performance penalty. |
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Question:
Can inline functions have a recursion? |
Answer:
No.
Syntax wise It is allowed. But then
the function is no longer Inline. As
the compiler will never know how deep
the recursion is at compilation time. |
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Question:
How do you link a C++ program to C
functions? |
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Answer:
By using
the extern "C" linkage specification
around the C function declarations.
Programmers should know about mangled
function names and type-safe linkages.
Then they should explain how the
extern "C" linkage specification
statement turns that feature off
during compilation so that the linker
properly links function calls to C
functions. Another acceptable answer
is "I don't know. We never had to do
that." Merely describing what a linker
does indicates that the programmer
does not understand the issue that
underlies the question. |
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Question:
Explain the scope resolution operator? |
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Answer:
It permits
a program to reference an identifier
in the global scope that has been
hidden by another identifier with the
same name in the local scope. |
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Question:
How many ways are there to initialize
an int with a constant? |
Answer:
Two:-
1. int foo = 123;
2. int bar(123); |
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Question:
What is your reaction to this line of
code?
delete this; |
Answer:
It is not
a good programming Practice.
A good programmer will insist that you
should absolutely never use the
statement if the class is to be used
by other programmers and instantiated
as static, extern, or automatic
objects. That much should be obvious.
The code has two built-in pitfalls.
First, if it executes in a member
function for an extern, static, or
automatic object, the program will
probably crash as soon as the delete
statement executes. There is no
portable way for an object to tell
that it was instantiated on the heap,
so the class cannot assert that its
object is properly instantiated.
Second, when an object commits suicide
this way, the using program might not
know about its demise. As far as the
instantiating program is concerned,
the object remains in scope and
continues to exist even though the
object did itself in. Subsequent
dereferencing of the pointer can and
usually does lead to disaster. I think
that the language rules should
disallow the idiom, but that's another
matter. |
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Question:
What is the difference between a copy
constructor and an overloaded
assignment operator? |
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Answer:
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. |
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Question:
When should you use multiple
inheritance? |
Answer:
There are
three acceptable answers:- "Never,"
"Rarely," and "When the problem domain
cannot be accurately modeled any other
way."
Consider an Asset class, Building
class, Vehicle class, and CompanyCar
class. All company cars are vehicles.
Some company cars are assets because
the organizations own them. Others
might be leased. Not all assets are
vehicles. Money accounts are assets.
Real estate holdings are assets. Some
real estate holdings are buildings.
Not all buildings are assets. Ad
infinitum. When you diagram these
relationships, it becomes apparent
that multiple inheritance is a likely
and intuitive way to model this common
problem domain. The applicant should
understand, however, that multiple
inheritance, like a chainsaw, is a
useful tool that has its perils, needs
respect, and is best avoided except
when nothing else will do. |
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Question:
What is a virtual destructor? |
Answer:
The simple
answer is that a virtual destructor is
one that is declared with the virtual
attribute.
The behavior of a virtual destructor
is what is important. If you destroy
an object through a pointer or
reference to a base class, and the
base-class destructor is not virtual,
the derived-class destructors are not
executed, and the destruction might
not be comple |
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Question:
Can a constructor throw a exception?
How to handle the error when the
constructor fails? |
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Answer:
The
constructor never throws a error. |
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Question:
How the compilers arranges the various
sections in the executable image? |
Answer:
The
executable had following sections:-
Data Section (uninitialized data
variable section, initialized data
variable section )
Code Section
Remember that all static variables are
allocated in the initialized variable
section. |
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Question:
When is a template a better solution
than a base class? |
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Answer:
When you
are designing a generic class to
contain or otherwise manage objects of
other types, when the format and
behavior of those other types are
unimportant to their containment or
management, and particularly when
those other types are unknown (thus,
the generality) to the designer of the
container or manager class. |
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Question:
What are the differences between a C++
struct and C++ class? |
Answer:
The
default member and base-class access
specifies are different.
This is one of the commonly
misunderstood aspects of C++. Believe
it or not, many programmers think that
a C++ struct is just like a C struct,
while a C++ class has inheritance,
access specifies, member functions,
overloaded operators, and so on.
Actually, the C++ struct has all the
features of the class. The only
differences are that a struct defaults
to public member access and public
base-class inheritance, and a class
defaults to the private access
specified and private base-class
inheritance. |
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Question:
How do you know that your class needs
a virtual destructor? |
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Answer:
If your
class has at least one virtual
function, you should make a destructor
for this class virtual. This will
allow you to delete a dynamic object
through a pointer to a base class
object. If the destructor is
non-virtual, then wrong destructor
will be invoked during deletion of the
dynamic object. |
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Question:
What is the difference between
new/delete and malloc/free? |
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Answer:
Malloc/free
do not know about constructors and
destructors. New and delete create and
destroy objects, while malloc and free
allocate and deallocate memory. |
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Question:
What happens when a function throws an
exception that was not specified by an
exception specification for this
function? |
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Answer:
Unexpected() is called, which, by
default, will eventually trigger
abort(). |
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Question:
Can you think of a situation where
your program would crash without
reaching the breakpoint, which you set
at the beginning of main()? |
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Answer:
C++ allows
for dynamic initialization of global
variables before main() is invoked. It
is possible that initialization of
global will invoke some function. If
this function crashes the crash will
occur before main() is entered. |
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Question:
What issue do auto_ptr objects
address? |
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Answer:
If you use auto_ptr objects you would
not have to be concerned with heap
objects not being deleted even if the
exception is thrown. |
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Question:
Is there any problem with the
following:
char *a=NULL; char& p = *a;? |
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Answer:
The result
is undefined. You should never do
this. A reference must always refer to
some object. |
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Question:
Why do C++ compilers need name
mangling? |
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Answer:
Name
mangling is the rule according to
which C++ changes function's name into
function signature before passing that
function to a linker. This is how the
linker differentiates between
different functions with the same
name. |
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Question:
Is there anything you can do in C++
that you cannot do in C? |
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Answer:
No. There
is nothing you can do in C++ that you
cannot do in C. After all you can
write a C++ compiler in C. |
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Question:
What is an object? |
Answer:
A
region of storage with associated
semantics.
For example, int i; "i is an object of
type int". In Object Oriented C++,
"object" usually means "an instance of
a class." Thus a class defines the
behavior of possibly many objects. |
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Question:
What is Dangling Pointer? |
Answer:
A
pointer which is pointing to an object
which no longer exists is a dangling
pointer.
MyClass* p(new MyClass);
MyClass* q = p;
delete p;
p->DoSomething(); // Watch out! p is
now dangling!
p = NULL; // p is no longer dangling
q->DoSomething(); // Ouch! q is still
dangling! |
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Question:
Why are member functions not virtual
by default? |
Answer:
Because many classes are not designed
to be used as base classes.
Also, objects of a class with a
virtual function require space needed
by
the virtual function call mechanism -
typically one word per object. This
overhead can be significant, and can
get in the way of layout
compatibility with data from other
languages. |
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Question:
Should I use NULL or 0? |
Answer:
In C++, the definition of NULL is 0,
so there is only an aesthetic
difference. I prefer to avoid macros,
so I use 0. Another problem with NULL
is that people sometimes mistakenly
believe that it is different from 0
and/or not an integer. In pre-standard
code, NULL was/is sometimes defined to
something unsuitable and therefore
had/has to be avoided.
That's less common these days. |
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Question:
What is faster ++i or i++, where i is
an interger variable? |
Answer:
The answer to this lies in the fact,
how they used. With ++i(PreIncrement)
the variable is incremented and new
value is returned. So it requires one
instruction to increment the variable.
In case of i++(post Increment), the
old value has to be returned or used
in the expression and then the
variable is incrememented after the
expression is evaluated. Since you
need one instruction to save the old
value to be used in the expression and
other instruction to increment the
variable, its comparatively slower. |
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Question:
Why is "this" not a reference? |
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Answer:
Because "this" was introduced into C++
before references were added. |
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Question:
How are C++ objects laid out in
memory? |
Answer:
Like C, C++ doesn't define layouts,
just semantic constraints that must be
met. Therefore different
implementations do things differently.
Unfortunately, the best explanation I
know of is in a book that is otherwise
outdated and doesn't describe any
current C++ implementation: The
Annotated C++ Reference Manual
(usually called the ARM). It has
diagrams of key layout examples. There
is a very brief explanation in Chapter
2 of TC++PL.
Basically, C++ constructs objects
simply by concatenating sub objects.
Thus
struct A { int a,b; };
is represented by two ints next to
each other, and
struct B : A { int c; };
is represented by an A followed by an
int; that is, by three ints next to
each other. Virtual functions are
typically implemented by adding a
pointer (the vptr) to each object of a
class with virtual functions. This
pointer points to the appropriate
table of functions (the vtbl). Each
class has its own vtbl shared by all
objects of that class. |
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Question:
Why doesn't C++ have an equivalent to
realloc()? |
Answer:
If you want to, you can of course use
realloc(). However, realloc() is only
guaranteed to work on arrays allocated
by malloc() (and similar functions)
containing objects without
user-defined copy constructors. Also,
please remember that contrary to naive
expectations, realloc() occationally
does copy its argument array.
In C++, a better way of dealing with
reallocation is to use a standard
library container, such as vector, and
let it grow naturally. |
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Question:
Can I mix C-style and C++ style
allocation and deallocation? |
Answer:
Yes, in the sense that you can use
malloc() and new in the same program.
No, in the sense that you cannot
allocate an object with malloc() and
free it using delete. Nor can you
allocate with new and delete with free
() or use realloc() on an array
allocated by new.
The C++ operators new and delete
guarantee proper construction and
destruction; where constructors or
destructors need to be invoked, they
are. The C-style functions malloc(),
calloc(), free(), and realloc()
doesn't ensure that. Furthermore,
there is no guarantee that the
mechanism use by new and delete to
acquire and release raw memory is
compatible with malloc() and free().
If mixing styles works on your system,
you were simply "lucky" - for now.
If you feel the need for realloc() -
and many do - then consider using a
standard library vector. For example
// read words from input into a vector
of strings:
vector words;
string s;
while (cin>>s && s!=".")
words.push_back(s);
The vector expands as needed. |
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Question:
What's the value of i++ + i++? |
Answer:
It's undefined. Basically, in C and
C++, if you read a variable twice in
an expression where you also write it,
the result is undefined. Don't do
that. Another example is:
v[i] = i++;
Related example:
f(v[i],i++);
Here, the result is undefined because
the order of evaluation of function
arguments are undefined. Having the
order of evaluation undefined is
claimed to yield better performing
code. Compilers could warn about such
examples, which are
typically subtle bugs (or potential
subtle bugs). I'm disappointed that
after decades, most compilers still
don't warn, leaving that job to
specialized, separate, and underused
tools. |
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Question:
Write a function to display an integer
in a binary format. |
Answer:
void displayBits( unsigned value )
{
const int SHIFT = 8 * sizeof( unsigned
) - 1;
const unsigned MASK = 1<< SHIFT;
cout << setw(10 ) << value << " = ";
for ( unsigned i = 1; i <= SHIFT + 1;
i++ )
{
cout << ( value & MASK ? '1' : '0' );
value <<= 1;
if ( i % 8 == 0 ) // output a space
after bits
cout << ' ';
}
cout << endl;
}
You can do the same using divide by 2,
until the number is greator than 0.
But you will have to use stack to
print it in reverse order. |
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Question:
What is
Memory Leak? |
Answer:
Memory which has no pointer pointing
to it and there is no way to delete or
reuse this memory(object), it causes
Memory leak.
{
Base *b = new base();
}
Out of this scope b no longer exists,
but the memory it was pointing to was
not deleted. Pointer b itself was
destroyed when it went out of scope. |
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Question:
Write the hello world program . . .
Without using any semi-colon's ";" ? |
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Answer:
#include
void main()
{
if(printf("Hello World")) { }
} |
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