Interview : C++ Interview Questions (Page - 2)
What are storage qualifiers in C++ ?
They are..
const
volatile
mutable
Const keyword indicates that memory once initialized, should not be altered by a
program. volatile keyword indicates that the value in the memory location can be
altered even though nothing in the program code modifies the contents. for
example if you have a pointer to hardware location that contains the time, where
hardware changes the value of this pointer variable and not the program. The
intent of this keyword to improve the optimization ability of the compiler.
mutable keyword indicates that particular member of a structure or class can be
altered even if a particular structure variable, class, or class member function
is constant.
struct data
{
char name[80];
mutable double salary;
}
const data MyStruct = { "Satish Shetty", 1000 }; //initlized by
complier strcpy ( MyStruct.name, "Shilpa Shetty"); // compiler error
MyStruct.salaray = 2000 ; // complier is happy allowed
What
is reference ?
reference is a
name that acts as an alias, or alternative name, for a previously defined
variable or an object. prepending variable with "&" symbol makes
it as reference. for
example:
int a;
int &b = a;
What is passing by reference?
Method of passing arguments to a function which takes parameter of type
reference. for
example:
void swap( int & x, int & y )
{
int temp = x;
x = y;
y = x;
}
int a=2, b=3;
swap( a, b );
Basically, inside the function there won't be any copy of the arguments
"x" and "y" instead they refer to original variables a and
b. so no extra memory needed to pass arguments and it is more efficient.
When do use "const" reference arguments in function?
a) Using const protects you against programming errors that inadvertently
alter data.
b) Using const allows function to process both const and non-const actual
arguments, while a function without const in the prototype can only accept non
constant arguments.
c) Using a const reference allows the function to generate and use a temporary
variable appropriately.
When are temporary variables created by C++ compiler?
Provided that function parameter is a "const reference", compiler
generates temporary variable in following 2 ways.
a) The actual argument is the correct type, but it isn't Lvalue
double Cuberoot ( const double & num )
{
num = num * num * num;
return num;
}
double temp = 2.0;
double value = cuberoot ( 3.0 + temp ); // argument is a expression and not a
Lvalue;
b) The actual argument is of the wrong type, but of a type that can be converted
to the
correct type
long temp = 3L;
double value = cuberoot ( temp); // long to double conversion
What
is virtual function?
When derived class
overrides the base class method by redefining the same function, then if client
wants to access redefined the method from derived class through a pointer from
base class object, then you must define this function in base class as virtual
function.
class parent
{
void Show()
{
cout << "i'm parent" << endl;
}
};
class child: public parent
{
void Show()
{
cout << "i'm child" << endl;
}
};
parent * parent_object_ptr = new child;
parent_object_ptr->show() // calls parent->show() i
now we goto virtual world...
class parent
{
virtual void Show()
{
cout << "i'm parent" << endl;
}
};
class child: public parent
{
void Show()
{
cout << "i'm child" << endl;
}
};
parent * parent_object_ptr = new child;
parent_object_ptr->show() // calls child->show()
What is pure virtual function? or what is abstract class?
When you define only function prototype in a base class without and do the
complete implementation in derived class. This base class is called abstract
class and client won't able to instantiate an object using this base class. You
can make a pure virtual function or abstract class this way..
class Boo
{
void foo() = 0;
}
Boo MyBoo; // compilation error
What is Memory alignment??
The term alignment primarily means the tendency of an address pointer value
to be a multiple of some power of two. So a pointer with two byte alignment has
a zero in the least significant bit. And a pointer with four byte alignment has
a zero in both the two least significant bits. And so on. More alignment means a
longer sequence of zero bits in the lowest bits of a pointer.
What problem does the namespace feature solve?
Multiple providers of libraries might use common global identifiers causing
a name collision when an application tries to link with two or more such
libraries. The namespace feature surrounds a library's external declarations
with a unique namespace that eliminates the potential for those collisions.
namespace [identifier] { namespace-body }
A namespace declaration identifies and assigns a name to a declarative region.
The identifier in a namespace declaration must be unique in the declarative
region in which it is used. The identifier is the name of the namespace and is
used to reference its members.
