Function overloading

Function Overloading

• In C++, two or more functions can share
the same name as long as their parameter
declarations are different.
• In this situation, the functions that share
the same name are said to be overloaded,
and the process is referred to as function
overloading

School of Computer Science sdandel.scs@dauniv.ac.in

• To see why function overloading is important,
first consider three functions defined by the C
subset: abs(), labs(), and fabs(). The abs()
function returns the absolute value of an
integer, labs() returns the absolute value of a
long, and fabs() returns the absolute value of a
double.
• Although these functions perform almost
identical actions, in C three slightly different
names must be used to represent these
essentially similar
tasks.
•Example: Function Overloading

Function Overloading

• Function overloading is the process of
using the same name for two or more
functions.
• The secret to overloading is that each
redefinition of the function must use
either-

• different types of parameters
• different number of parameters.

Function Overloading and
Ambiguity

• Ambiguous statements are errors, and
programs containing ambiguity will not
compile.
• By far the main cause of ambiguity
involves C++'s automatic type
conversions.


Function Overloading and
Ambiguity
• void f(int x);
• void f(int &x); // error

• two functions cannot be overloaded when
the only difference is that one takes a
reference parameter and the other takes a
normal, call-by-value parameter.


• // This program contains an error.
• #include <iostream>
• using namespace std;
• void f(int x);
• void f(int &x); // error
• int main()
• {
• int a=10;
• f(a); // error, which f()?
• return 0;
• }
• void f(int x)
• {
• cout << "In f(int)n";
• }
• void f(int &x)
• {
• cout << "In f(int &)n";
• }


• char myfunc(unsigned char ch);
• char myfunc(char ch);
• In C++, unsigned char and char are
not inherently ambiguous.


• char myfunc(unsigned char ch);
• char myfunc(char ch);
• int main()
• {
• cout << myfunc('c'); // this calls myfunc(char)
• cout << myfunc(88) << " "; // ambiguous
• return 0;
• }
• char myfunc(unsigned char ch)
• {
• return ch-1;
• }
• char myfunc(char ch)
• {
• return ch+1;
• }


• float myfunc(float i);
• double myfunc(double i);
• int main()
• {
• cout << myfunc(10.1) << " "; // unambiguous, calls
myfunc(double)
• cout << myfunc(10); // ambiguous
• return 0;
• }
• float myfunc(float i)
• {
• return i;
• }
• double myfunc(double i)
• {
• return -i;
• }


Others
• Typedef int integer;
• Enum days{mon,tue,wed}
• Void f(int);
• Void f(mon);


Overloading Constructor Functions

• Many times you will create a class for which
there are two or more possible ways to
construct an object.
• In these cases, you will want to provide an
overloaded constructor function for each way.
• The user is free to choose the best way to
construct an object given the specific
circumstance.

Copy Constructors

• By default, when one object is used to initialize
another.
• C++ performs a bitwise copy.
• For Example: MyClass B= A;
• If a bitwise copy is performed, then B will be an
exact copy of A. This means that B will be using the
same piece of allocated memory that A is using,
instead of allocating its own.
• If MyClass includes a destructor that frees the
memory, then the same piece of memory will be
freed twice when A and B are destroyed!

Copy Constructor…….
• The same type of problem can occur in two
additional ways:
• first, when a copy of an object is made when it
is passed as an argument to a function;
• second, when a temporary object is created as a
return value from a function.
• To solve the type of problem just described, C++
allows you to create a copy constructor, which
the compiler uses when one object initializes
another.


• The most common general form of a copy
constructor is
– classname (const classname &o) {
– // body of constructor
–}
• Here, o is a reference to the object on the
right side of the initialization.
• It is permissible for a copy constructor to have
additional parameters as long as they have
default
arguments defined for them.
• However, in all cases the first parameter must
be a
reference to the object doing the initializing.

• It is important to understand that C++ defines
two distinct types of situations in which the
value of one object is given to another.
• The first is assignment.
• The second is initialization, which can occur
any of three ways:
• myclass x = y; // y explicitly initializing x
• func(y); // y passed as a parameter
• y = func(); // y receiving a temporary,
return object


Example: copy_cons1
• The copy constructor is called, memory for the new
array is allocated and stored in x.p, and the
contents of num are copied to x's array.
• In this way, x and num have arrays that contain the
same values, but each array is separate and
distinct.
• If the copy constructor had not been created, the
default bitwise initialization would have resulted in x
and num sharing the same memory for their arrays.
• array a(10);
• // ...
• array b(10);
• b = a; // does not call copy constructor

Finding the Address of an
Overloaded Function
• You can obtain the address of a function.
• Assign the address of the function to a pointer and then
call that function through that pointer
• When you assign the address of an overloaded function
to a function pointer, it is the declaration of the pointer
that determines which function's address is obtained.
• Further, the declaration of the function pointer must
exactly match one and only one of the overloaded
function's declarations.
• Example:


Default Function Arguments

• C++ allows a function to assign a parameter
a default value when no argument
corresponding to that parameter is specified
in a call to that function.
• The default value is specified in a manner
syntactically similar to a variable
initialization


Example:
void myfunc(double d = 0.0)
{
// ...
}
• Now, myfunc() can be called one of two ways, as the
following examples show:
– myfunc(198.234); // pass an explicit value
– myfunc(); // let function use default
• The first call passes the value 198.234 to d.
• The second call automatically gives d the
default value zero.


• There are two advantages to including
default arguments, when appropriate, in a
constructor function.
• First, they prevent you from having to
provide an overloaded constructor that
takes no parameters.
• Second, defaulting common initial values
is more convenient than specifying them
each time an object is declared.
• In some situations, default arguments can
be used as a shorthand form of function
overloading.

Operator Overloading.

• In C++, you can overload most operators
so that they perform special operations
relative to classes that you create.
• For example, a class that maintains a
stack might overload + to perform a push
operation and – – to perform a pop.


Overloadable operators.
Unary: + - * ! ~ & ++ -- () -> ->*

new delete

Binary: + - * / % & | ^ << >>

= += -= /= %= &= |= ^= <<= >>=

== != < > <= >= && || [] () ,


• You overload operators by creating
operator functions.
• An operator function defines the
operations that the overloaded operator
will perform relative to the class upon
which it will work.
• An operator function is created using
the keyword operator.
• Operator functions can be either
members or nonmembers of a class.
• Nonmember operator functions are
almost always friend functions of the
class,

Creating a Member Operator
Function
• A member operator function takes this
general form:
• ret-type class-name::operator#(arg-
list)
•{
• // operations
•}


• Often, operator functions return an object of
the class they operate on, but ret-type can
be any valid type.
• The # is a placeholder. When you create an
operator function, substitute the operator for
the #.
• For example, if you are overloading the /
operator, use operator/.
• When you are overloading a unary operator,
arg-list will be empty.
• When you are overloading binary operators,
arg-list will contain one parameter.

of the
Increment and Decrement
Operators
• In older versions of C++, it was not possible to
specify separate prefixand postfixversions of an
overloaded ++ or – –.
• The prefix form was used for both.
• The posfix is declared like this:
– loc operator++(int x);
• If the ++ precedes its operand, the operator++()
function is called.
• If the ++ follows its operand, the
operator++(int x) is called and x has the value
zero.

Decrement
// Prefix decrement
type operator– –( ) {
// body of prefix operator
}
// Postfix decrement
type operator– –(int x) {
// body of postfix operator
}


Overloading the Shorthand
Operators
• You can overload any of C++'s "shorthand"
operators, such as +=, –=, and the like.
• For example, this function overloads += relative
to loc:
• loc loc::operator+=(loc op2)
•{
• longitude = op2.longitude + longitude;
• latitude = op2.latitude + latitude;
• return *this;
•}


Operator Overloading Restrictions

• You cannot alter the precedence of an
operator.
• You cannot change the number of operands
that an operator takes.
• Except for the function call operator functions
cannot have default arguments.
• Finally, these operators cannot be
overloaded:
. .* :: ?: sizeof

Friend operator funcions
• There are some restrictions that apply to
friend operator functions.
• First, you may not overload the =, ( ), [ ],
or –> operators by using a friend function.
• Second, when overloading the increment
or decrement operators, you will need to
use a reference parameter when using a
friend function.


Using a Friend to Overload ++ or –
–
• If you want to use a friend function to
overload the increment or decrement
operators, you must pass the operand as
a reference parameter.
• This is because friend functions do not
have this pointers.


Friend Operator Functions Add
Flexibility
• Ob + 100 // valid
• 100 + Ob // invalid
• To allow both object+integer and integer+object,
simply overload the function twice—one version
for each situation.
• Thus, when you overload an operator by using
two friend functions, the object may appear on
either the left or right side of the operator.


Overloading new and delete

• The skeletons for the functions that overload new and delete
are shown here:
// Allocate an object.
void *operator new(size_t size)
{
/* Perform allocation. Throw bad_alloc on failure.
Constructor called automatically. */
return pointer_to_memory;
}
// Delete an object.
void operator delete(void *p)
{
/* Free memory pointed to by p.
Destructor called automatically. */
}


New Delete

• The type size_t is a defined type capable of
containing the largest single piece of memory
that can be allocated. (size_t is essentially an
unsigned integer.)
• The parameter size will contain the number
of bytes needed to hold the object being
allocated.
• The overloaded new function must return a
pointer to the memory that it allocates, or
throw a bad_alloc exception if an allocation
error occurs.

Overloading Some Special
Operators
• Overloading [ ]
• type class-name::operator[](int i)
• {
• // . . .
• }
• Technically, the parameter does not have to
be of type int, but an operator[ ]() function is
typically used to provide array subscripting,
and as such, an integer value is generally
used.
• Given an object called O, the expression
• O[3] translates into this call to the operator[
]() function:
• O.operator[](3)

Overloading ( )

• Given the overloaded operator function
declaration
• double operator()(int a, float f, char *s);
• and an object O of its class, then the
statement
• O(10, 23.34, "hi");
• translates into this call to the operator()
function.
• O.operator()(10, 23.34, "hi");
• In general, when you overload the ( )
operator, you define the parameters that you
want to pass to that function. When you use
the ( ) operator in your program, the

Overloading –>

• The –> pointer operator, also called the class
member access operator, is considered a
unary operator when overloading. Its general
usage is shown here:
• object->element;
• Here, object is the object that activates the
call. The operator–>() function must return a
pointer to an object of the class that
operator–>() operates upon.
• The element must be some member
accessible within the object.


Overloading the Comma Operator

• If you want the overloaded comma to
perform in a fashion similar to its normal
operation, then your version must
discard the values of all operands
except the rightmost.
• The rightmost value becomes the result
of the comma operation.


Inheritance


Inheritance
• It allows the creation of hierarchical
classifications.
• Using inheritance, you can create a
general class that defines traits common
to a set of related items.
• This class may then be inherited by other,
more specific classes, each adding only
those things that are unique to the
inheriting class.


Inheritance
• A class that is inherited is referred to as a
base class.
• The class that does the inheriting is called
the derived class.
• Further, a derived class can be used as a
base class for another derived class. In
this way, multiple inheritance is achieved.


Base-Class Access Control

• When a class inherits another, the members of
the base class become members of the derived
class.
• Class inheritance uses this general form:
class derived-class-name : access base-class-name {
// body of class
};
• The access status of the base-class members
inside the derived class is determined by access.


• The base-class access specifier must be
either public, private, or protected.
• If no access specifier is present, the
access specifier is private by default if the
derived class is a class.
• If the derived class is a struct, then public
is the default in the absence of an explicit
access specifier.


What to inherit?

• In principle, every member of a base class
is inherited by a derived class
– just with different access permission


Access Control Over the Members

• Two levels of access control
base class/ superclass/ over class members
parent class – class definition
– inheritance type
members goes to
derive from

class Point{
protected: int x, y;
public: void set(int a, int b);
};
derived class/ subclass/
child class class Circle : public Point{
……
};

Even more …

• A derived class can override methods defined in its
parent class. With overriding,
– the method in the subclass has the identical signature to the
method in the base class.
– a subclass implements its own version of a base class
method.
class A {
class B : public A {
protected:
public:
int x, y;
void print ()
public:
{cout<<“From B”<<endl;}
void print ()
};
{cout<<“From A”<<endl;}
};


Private, Public, and Protected
Base Classes
• A base class may be specified to be private,
public, or protected. Unless so specified, the
base class is assumed to be private:
class A {
private:
int x;
void Fx (void);
public:
int y;
void Fy (void);
protected:
int z;
void Fz (void);
};

class B : A {}; // A is a private base class of B
class C : private A {}; // A is a private base
class of C

• The behavior of these is as follows :
• All the members of a private base class
become private members of the derived
class. So x, Fx, y, Fy, z, and Fz all become
private members of B and C.


class D : public A {}; // A is a public base class of D

• The members of a public base class keep their
access characteristics in the derived class. So,
x and Fx becomes private members of D, y and
Fy become public members of D, and z and Fz
become protected members of D.


class E : protected A {}; // A is a protected
base class of E

• The private members of a protected base class
become private members of the derived class.
Whereas, the public and protected members of a
protected base class become protected
members of the derived class. So, x and Fx
become private members of E, and y, Fy, z, and
Fz become protected members of E.


Base class access inheritance rules.

Private Public Derived Protected
Base Class Derived Derived

Private Member private private private

Public Member private public protected

Protected private protected protected
Member


Private access specifier
• When the base class is inherited by using the
private access specifier, all public and
protected members of the base class become
private members of the derived class.Example:
• When a base class' access specifier is private,
public and protected members of the base
become private members of the derived class.
• This means that they are still accessible by
members of the derived class but cannot be
accessed by parts of your program that are not
members of either the base or derived class.


• It is also possible to individually exempt a base
class member from the access changes
specified by a derived class, so that it retains its
original access characteristics. To do this, the
exempted member is fully named in the derived
class under its original access characteristic. For
example:
class C : private A {
//...
public: A::Fy; // makes Fy a public member of C
protected:A::z; // makes z a protected member of C
};


Inheritance and protected Members

• When a member of a class is declared as
protected, that member is not accessible by
other, nonmember elements of the program.
• With one important exception, access to a
protected member is the same as access to a
private member—it can be accessed only by
other members of its class. The sole exception
to this is when a protected member is inherited.


Protected in Public Inheritance
• When a derived class is used as a base
class for another derived class, any
protected member of the initial base class
that is inherited (as public) by the first
derived class may also be inherited as
protected again by a second derived class.


Protected Base-Class Inheritance

• It is possible to inherit a base class as
protected.
• When this is done, all public and protected
members of the base class become
protected members of the derived class.
• For example,


Inheriting Multiple Base Classes

• It is possible for a derived class to inherit two
or more base classes.
• To inherit more than one base class, use a
comma-separated list.
• Further, be sure to use an access-specifier
for each base inherited.


Multiple Inheritance
• Multiple inheritance
– Derived class has several base classes
– Powerful, but can cause ambiguity problems
• If both base classes have functions of the same
name
• Solution: specify exact function using ::
– myObject.BaseClass1::function()

– Format
• Use comma-separated list
class Derived : public Base1, public Base2{
contents
}

Constructors and Destructors

• When an object of a derived class is created, the
base class constructor is applied to it first,
followed by the derived class constructor.
• When the object is destroyed, the destructor of
the derived class is applied first, followed by the
base class destructor.
• Constructors are applied in order of derivation
and destructors are applied in the reverse order.


• class A { /* ... */ }
• class B : public A { /* ... */ }
• class C : public B { /* ... */ }
c being constructed c being destroyed

A::A A::~A

B::B B::~B

C::C ......... C::~C


Constructors: Multi level Inheritance
• In cases of multiple inheritance (that is,
where a derived class becomes the base
class for another derived class), the
general rule applies:
• Constructors are called in order of
derivation, destructors in reverse order.
For example,


Constructors: Multiple Inheritance
• Constructors are called in order of derivation, left to
right, as specified in derived's inheritance list.
• Destructors are called in reverse order, right to left.
• class derived: public base2, public base1
then the output of this program would have looked
like this:
Constructing base2
Constructing base1
Constructing derived
Destructing derived
Destructing base1
Destructing base2


Passing Parameters to Base-Class
Constructors
derived-constructor(arg-list) : base1(arg-list),
base2(arg-list),
// ...
baseN(arg-list)
{
// body of derived constructor
}


Virtual Base Classes

• An element of ambiguity can be introduced
into a C++ program when multiple base
classes are inherited.
• Example: Ambiguity
• There are two ways to remedy the preceding
program.
• The first is to apply the scope resolution
operator to i and manually select one i.


Virtual Base Classes
• When two or more objects are derived from a
common base class, you can prevent multiple
copies of the base class from being present in
an object derived from those objects by
declaring the base class as virtual when it is
inherited.
• You accomplish this by preceding the base
class' name with the keyword virtual when it is
inherited.
• Inherited base as virtual, any multiple
inheritance involving them will cause only one
copy of base to be present.


Thus,
• The only difference between a normal
base class and a virtual one is what
occurs when an object inherits the base
more than once.
• If virtual base classes are used, then only
one base class is present in the object.
• Otherwise, multiple copies will be found.


Run Time Polymorphism
(Virtual Functions)

• Polymorphism is supported by C++ both at
compile time and at run time.
• Compile-time polymorphism is achieved
by overloading functions and operators.
• Run-time polymorphism is accomplished
by using inheritance and virtual functions.


Virtual Functions

• A virtual function is a member function that is
declared within a base class and redefined by
a derived class.
• To create a virtual function, precede the
function's declaration in the base class with
the keyword virtual.
• When a class containing a virtual function is
inherited, the derived class redefines the
virtual function to fit its own needs.


Virtual Functions

• In essence, virtual functions implement the "one
interface, multiple methods" philosophy that
underlies polymorphism.
• The virtual function within the base class defines
the form of the interface to that function.
• Each redefinition of the virtual function by a
derived class implements its operation as it
relates specifically to the derived class.


Virtual Functions

• When accessed "normally," virtual functions
behave just like any other type of class
member function.
• However, what makes virtual functions
important and capable of supporting run-
time polymorphism is how they behave
when accessed via a pointer.


Virtual Functions

• When a base pointer points to a derived object
that contains a virtual function, C++ determines
which version of that function to call based
upon the type of object pointed to by the pointer.
• And this determination is made at run time.
• Thus, when different objects are pointed to,
different versions of the virtual
function are executed.


Virtual Function vs Function
Overloading
• At first glance, the redefinition of a virtual
function by a derived class appears similar
to function overloading.
• However, this is not the case, and the
term overloading is not applied to virtual
function redefinition because several
differences exist.


Virtual Function vs Function
Overloading
• The prototype for a redefined virtual
function must match exactly the prototype
specified in the base class.
• This differs from overloading a normal
function, in which return types and the
number and type of parameters may differ.
• The term overriding is used to describe
virtual function redefinition by a derived
class.


Differences
• When a virtual function is redefined, all aspects
of its prototype must be the same.
• If you change the prototype when you attempt to
redefine a virtual function, the function will
simply be considered overloaded by the C++
compiler, and its virtual nature will be lost.
• Another important restriction is that virtual
functions must be non static members of the
classes of which they are part.
• They cannot be friends.
• Constructor functions cannot be virtual, but
destructor functions can.


Calling a Virtual Function Through a
Base Class Reference

• Polymorphic nature of a virtual function is also
available when called through a base-class
reference.
• A base-class reference can be used to refer to an
object of the base class or any object derived
from that base.
• When a virtual function is called through a base-
class reference, the version of the function
executed is determined by the object being
referred to at the time of the call.


The Virtual Attribute Is Inherited

• When a virtual function is inherited, its virtual
nature is also inherited.
• This means that when a derived class that has
inherited a virtual function is itself used as a
base class for another derived class, the virtual
function can still be overridden.
• Put differently, no matter how many times a
virtual function is inherited, it remains virtual.


Virtual Functions Are Hierarchical

• When a function is declared as virtual by a base
class, it may be overridden by a derived class.
• However, the function does not have to be
overridden.
• When a derived class fails to override a virtual
function, then when an object of that derived
class accesses that function, the function
defined by the base class is used.
• Example1:


Virtual Functions Are Hierarchical

• Because inheritance is hierarchical in C++, it
makes sense that virtual functions are also
hierarchical.
• This means that when a derived class fails to
override a virtual function, the first redefinition
found in reverse order of derivation is used.
• Example2:


Pure Virtual Functions

• In many situations there can be no meaningful
definition of a virtual function within a base class.
• For example, a base class may not be able to
define an object sufficiently to allow a base-class
virtual function to be created.
• Further, in some situations you will want to
ensure that all derived classes override a virtual
function.
• To handle these two cases, C++ supports the
pure virtual function.


Pure Virtual Functions

• A pure virtual function is a virtual function that
has no definition within the base class.
• To declare a pure virtual function, use this
general form:
virtual type func-name(parameter-list) = 0;
• When a virtual function is made pure, any
derived class must provide its own definition.
• If the derived class fails to override the pure
virtual function, a compile-time error will result.


Abstract Classes

• A class that contains at least one pure virtual
function is said to be abstract.
• Because an abstract class contains one or more
functions for which there is no definition (that is,
a pure virtual function), no objects of an abstract
class may be created.
• Instead, an abstract class constitutes an
incomplete type that is used as a foundation for
derived classes.


Abstract Classes

• Although you cannot create objects of an
abstract class, you can create pointers
and references to an abstract class.
• This allows abstract classes to support
run-time polymorphism, which relies upon
base-class pointers and references to
select the proper virtual function.


Early vs. Late Binding

• Early binding refers to events that occur at compile time.
In essence, early binding occurs when all information
needed to call a function is known at compile time.
• Early binding means that an object and a function call
are bound during compilation.)
• Examples of early binding include normal function calls
(including standard library functions), overloaded
function calls, and overloaded operators.
• The main advantage to early binding is efficiency.
• Because all information necessary to call a function is
determined at compile time, these types of function calls
are very fast.


Early vs. Late Binding

• The opposite of early binding is late binding. As it relates to C++,
late binding refers to function calls that are not resolved until run
time.
• Virtual functions are used to achieve late binding.
• As you know, when access is via a base pointer or reference, the
virtual function actually called is determined by the type of object
pointed to by the pointer.
• Because in most cases this cannot be determined at compile time,
the object and the function are not linked until run time.
• The main advantage to late binding is flexibility.
• Unlike early binding, late binding allows you to create programs that
can respond to events occurring while the program executes without
having to create a large amount of "contingency code."
• Keep in mind that because a function call is not resolved until run
time, late binding can make for somewhat slower execution times.


Generic Functions(Templates)

• Through a generic function, a single general
procedure can be applied to a wide range of
data.
• By creating a generic function, you can define
the nature of the algorithm, independent of any
data.
• Once you have done this, the compiler will
automatically generate the correct code for the
type of data that is actually used when you
execute the function.


Generic Functions

• A generic function is created using the
keyword template.
• The normal meaning of the word "template"
accurately reflects its use in C++.
• It is used to create a template (or framework)
that describes what a function will do.


Generic Functions

• The general form of a template function definition is shown here:
template <class Ttype>
ret-type func-name(parameter list)
{
// body of function
}
• Here, Ttype is a placeholder name for a data type used by the
function.
• This name may be used within the function definition.
• However, it is only a placeholder that the compiler will automatically
replace with an actual data type when it creates a specific version of
the function.
• Example: Swap


• Because swapargs() is a generic function,
the compiler automatically creates three
versions of swapargs() : one that will
exchange integer values, one that will
exchange floating-point values, and one
that will swap characters.


Generic Function Restrictions

• Generic functions are similar to overloaded
functions except that they are more
restrictive.
• When functions are overloaded, you may
have different actions performed within the
body of each function.
• But a generic function must perform the
same general action for all versions—only
the type of data can differ.


Generic Classes

• Generic classes are useful when a class
uses logic that can be generalized.
• For example, the same algorithms that
maintain a queue of integers will also work
for a queue of characters, and the same
mechanism that maintains a linked list of
mailing addresses will also maintain a
linked list of auto part information.


Generic Classes

• The general form of a generic class declaration
is shown here:
template <class Ttype> class class-name {
.
..
}
• Here, Ttype is the placeholder type name, which
will be specified when a class is instantiated.
• If necessary, you can define more than one
generic data type using a comma-separated list.


Generic Classes
• Once you have created a generic class, you
create a specific instance of that class using the
following general form:

class-name <type> ob;

• Here, type is the type name of the data that the
class will be operating upon.
• Member functions of a generic class are
themselves automatically generic.
• You need not use template to explicitly specify
them as such.


Example Stack Template
• Two are integer stacks. Two are stacks of
• doubles. Pay special attention to these declarations:
• stack<char> s1, s2; // create two character stacks
• stack<double> ds1, ds2; // create two double stacks
• Notice how the desired data type is passed inside the
angle brackets. By changing the
• type of data specified when stack objects are created,
you can change the type of data
• stored in that stack. For example, by using the following
declaration, you can create
• another stack that stores character pointers.
• stack<char *> chrptrQ;


Example Stack Template
• You can also create stacks to store data types that you
create. For example, if you want to use the following
structure to store address information,
struct addr {
char name[40];
char street[40];
char city[30];
char state[3];
char zip[12];
};
• then to use stack to generate a stack that will store
objects of type addr, use a declaration like this:
• stack<addr> obj;
• An Example with Two Generic Data Types:


The Power of Templates

• Templates help you achieve one of the most
elusive goals in programming: the creation of
reusable code.
• Through the use of template classes you can
create frameworks that can be applied over and
over again to a variety of programming situations.
• Once you have written and debugged a template
class, you have a solid software component that
you can use with confidence in a variety of
different situations.


The Power of Templates

• Template functions and classes are
already becoming commonplace in
programming, and this trend is expected to
continue.
• For example, the STL (Standard Template
Library) defined by C++ is, as its name
implies, built upon templates.


Exception Handling Fundamentals

• C++ exception handling is built upon three
keywords: try, catch, and throw.
• In the most general terms, program statements
that you want to monitor for exceptions are
contained in a try block.
• If an exception (i.e., an error) occurs within the
try block, it is thrown (using throw).
• The exception is caught, using catch, and
processed.


Exception Handling Fundamentals
• Code that you want to monitor for exceptions
must have been executed from within a try
block. (Functions called from within a try
block may also throw an exception.)
• Exceptions that can be thrown by the
monitored code are caught by a catch
statement, which immediately follows the try
statement in which the exception was
thrown.


• The general form of try and catch are shown here.
try {
// try block
}
catch (type1 arg) {
// catch block
}
catch (type2 arg) {
// catch block
}
catch (type3 arg) {
// catch block
}
..
.
catch (typeN arg) {
// catch block
}


Try
• The try can be as short as a few
statements within one function or as all
encompassing as enclosing the main()
function code within a try block (which
effectively causes the entire program to be
monitored).


Catch
• When an exception is thrown, it is caught by its
corresponding catch statement, which processes the
exception.
• There can be more than one catch statement associated
with a try.
• Which catch statement is used is determined by the type
of the exception.
• That is, if the data type specified by a catch matches
that of the exception, then that catch statement is
executed (and all others are bypassed).
• When an exception is caught, arg will receive its value.
Any type of data may be caught, including classes that
you create.
• If no exception is thrown (that is, no error occurs within
the try block), then no catch statement is executed.


Throw
• The general form of the throw statement is shown here:
throw exception;
• throw generates the exception specified by exception.
• If this exception is to be caught, then throw must be
executed either from within a try block itself, or from any
function called from within the try block (directly or
indirectly).
• If you throw an exception for which there is no applicable
catch statement, an abnormal program termination may
occur.
• Throwing an unhandled exception causes the standard
library function terminate() to be invoked.


Example:
// A simple exception handling example.
#include <iostream>
using namespace std;
int main()
{
cout << "Startn";
try { // start a try block
cout << "Inside try blockn";
throw 100; // throw an error
cout << "This will not execute";
}
catch (int i) { // catch an error
cout << "Caught an exception -- value is: ";
cout << i << "n";
}
cout << "End";
return 0;
}


Output
• This program displays the following output:
Start
Inside try block
Caught an exception -- value is: 100
End


Example 2
// This example will not work.
#include <iostream>
int main()
{
cout << "Startn";
throw 100; // throw an error
cout << "This will not execute";
}
catch (double i) { // won't work for an int exception
cout << i << "n";
}
cout << "End";
return 0;
}


Output
• This program produces the following
output because the integer exception will
not be caught by the catch(double i)
statement.
Start
Inside try block
Abnormal program termination


Throwing an exception from a function outside the
try block.
#include <iostream>
void Xtest(int test)
{
cout << "Inside Xtest, test is: " << test << "n";
if(test) throw test;
}
int main()
{
cout << "Startn";
Xtest(0);
Xtest(1);
Xtest(2);
}
catch (int i) { // catch an error
cout << i << "n";
}
cout << "End";
return 0;
}

Output
output:
Start
Inside try block
Inside Xtest, test is: 0
Inside Xtest, test is: 1
Caught an exception -- value is: 1
End


Using Multiple catch Statements
void Xhandler(int test)
{
try{
if(test) throw test;
else throw "Value is zero";
}
catch(int i) {
cout << "Caught Exception #: " << i << 'n';
}
catch(const char *str) {
cout << "Caught a string: ";
cout << str << 'n';
}
}


int main()
{
cout << "Startn";
Xhandler(1);
Xhandler(2);
Xhandler(0);
Xhandler(3);
cout << "End";
return 0;
}


Output
output:
Start
Caught Exception #: 1
Caught a string: Value is zero
End


Handling Derived-Class Exceptions
// Catching derived classes.
#include <iostream>
class B {
};
class D: public B {
};
int main()
{
D derived;
try {
throw derived;
}
catch(B b) {
cout << "Caught a base class.n";
}
catch(D d) {
cout << "This won't execute.n";
}
return 0;
}


Catching All Exceptions

• In some circumstances you will want an
exception handler to catch all exceptions
instead of just a certain type.

catch(...) {
// process all exceptions
}


Example:
try{
if(test==0) throw test; // throw int
if(test==1) throw 'a'; // throw char
if(test==2) throw 123.23; // throw double
}
catch(...) { // catch all exceptions
cout << "Caught One!n";
}


Namespaces

• Purpose is to localize the names of
identifiers to avoid name collisions.
• The C++ programming environment has
seen an explosion of variable, function,
and class names.
• Prior to the invention of namespaces, all of
these names competed for slots in the
global namespace and many conflicts
arose.


Namespaces

• For example, if your program defined a function
called abs() , it could (depending upon its
parameter list) override the standard library
function abs() because both names would be
stored in the global namespace.
• Name collisions were compounded when two or
more third-party libraries were used by the same
program.
• The situation can be particularly troublesome for
class names.


• Prior to namespace, the entire C++ library was
defined within the global namespace (which was, of
course, the only namespace).
• Since the addition of namespace, the C++ library is
now defined within its own namespace, called std,
which reduces the chance of name collisions.
• You can also create your own namespaces within
your program to localize the visibility of any names
that you think may cause conflicts.
• This is especially important if you are creating class
or function libraries.


Namespace Fundamentals
• The namespace keyword allows you to
partition the global namespace by creating
a declarative region.
• In essence, a namespace defines a
scope. The general form of namespace is
shown here:
namespace name {
// declarations
}
• Anything defined within a namespace statement is
within the scope of that namespace.


Example:
namespace CounterNameSpace {
int upperbound;
int lowerbound;
class counter {
int count;
public:
counter(int n) {
if(n <= upperbound) count = n;
else count = upperbound;
}
void reset(int n) {
if(n <= upperbound) count = n;
}
int run() {
if(count > lowerbound) return count--;
else return lowerbound;
}
};
}


int main()
{
CounterNameSpace::upperbound = 100;
CounterNameSpace::lowerbound = 0;
CounterNameSpace::counter ob1(10);
int i;
do {
i = ob1.run();
cout << i << " ";
} while(i > CounterNameSpace::lowerbound);
cout << endl;
CounterNameSpace::counter ob2(20);
do {
i = ob2.run();
cout << i << " ";
cout << endl;
ob2.reset(100);
CounterNameSpace::lowerbound = 90;
do {
i = ob2.run();
cout << i << " ";
return 0;
}


using
• Having to specify the namespace and the
scope resolution operator each time you
need to refer to one quickly becomes a
tedious chore.
• The using statement was invented to
alleviate this problem.
• The using statement has these two
general forms:
• using namespace name;
• using name::member;


Namespaces

• Namespaces allow to group entities like classes,
objects and functions under a name.
• This way the global scope can be divided in
"sub-scopes", each one with its own name.
• The format of namespaces is:
namespace identifier
{
entities
}


• For example:
• namespace myNamespace
{
int a, b;
}
• In this case, the variables a and b are normal
variables declared within a namespace called
myNamespace.
• In order to access these variables from outside
the myNamespace namespace we have to use
the scope operator ::


• // namespaces
#include <iostream>
namespace first
{ int var = 5; }
namespace second
{ double var = 3.1416; }
int main ()
{
cout << first::var << endl;
cout << second::var << endl;
return 0;
}
//No redefinition errors happen thanks to namespaces.


• // using
#include <iostream>
namespace first
{ int x = 5; int y = 10; }
namespace second
{ double x = 3.1416; double y = 2.7183; }
int main ()
{
using first::x;
using second::y;
cout << x << endl; cout << y << endl;
cout << first::y << endl; cout << second::x << endl;
return 0;
}


• The keyword using can also be used as a directive to
introduce an entire namespace:
• // using
#include <iostream>
namespace first
{ int x = 5; int y = 10; }
namespace second
{ double x = 3.1416; double y = 2.7183; }
int main ()
{
using namespace first;
cout << x << endl; cout << y << endl;
cout << second::x << endl; cout << second::y << endl;
return 0;
} School of Computer Science sdandel.scs@dauniv.ac.in

• using and using namespace have validity
only in the same block in which they are
stated
• For example, if we had the intention to first
use the objects of one namespace and then
those of another one, we could do
something like:


• // using namespace example
#include <iostream>
namespace first
{ int x = 5; }
namespace second { double x = 3.1416; }
int main () {
{
using namespace first;
cout << x << endl;
}
{
using namespace second;
cout << x << endl;
}
return 0;
}


Namespace alias
• We can declare alternate names for
existing namespaces according to the
following format:

• namespace new_name = current_name;


Namespace std
• All the files in the C++ standard library
declare all of its entities within the std
namespace.
• That is why we have generally included
the using namespace std;


• In the first form, name specifies the name
of the namespace you want to access.
• All of the members defined within the
specified namespace are brought into view
(i.e., they
become part of the current namespace)
and may be used without qualification.
• In the second form, only a specific
member of the namespace is made
visible.


Standard Template Library (STL).

• It provides general-purpose, templatized classes
and functions that implement many popular and
commonly used algorithms and data structures,
including, for example, support for vectors, lists,
queues, and stacks.
• Because the STL is constructed from template
classes, the algorithms and data structures can
be applied to nearly any type of data.
• At the core of the standard template library are
three foundational items: containers,
algorithms, and iterators.


Containers

• Containers are objects that hold other objects,
and there are several different types.
• For example, the vector class defines a
dynamic array, deque creates a double-ended
• queue, and list provides a linear list.
• These containers are called sequence
containers because in STL terminology, a
sequence is a linear list.


Algorithms

• Algorithms act on containers. They provide
the means by which you will manipulate
the contents of containers.
• Their capabilities include initialization,
sorting, searching, and transforming the
contents of containers.


Iterators

• Iterators are objects that are, more or less,
pointers.
• They give you the ability to cycle through
the contents of a container in much the
same way that you would use a pointer to
cycle through an array.


The Container Classes


• Since the names of the
generic placeholder types
in a template class
declaration are arbitrary,
the container classes
declare typedefed
versions of these types.
• This makes the type
names concrete. Some of
the most common
typedef names are
shown here:


General Theory of Operation

• First, you must decide on the type of container
that you wish to use.
• Once you have chosen a container, you will use
its member functions to add elements to the
container, access or modify those elements, and
delete elements.
• One of the most common ways to access the
elements within a container is through an iterator.
• The sequence and the associative containers
provide the member functions begin() and end() ,
which return iterators to the start and end of the
container, respectively.


Example: Vectors
• The vector class supports a dynamic array.
• This is an array that can grow as needed. As
you know, in C++ the size of an array is fixed at
compile time.
• While this is by far the most efficient way to
implement arrays, it is also the most restrictive
because the size of the array cannot be
• adjusted at run time to accommodate changing
program conditions.
• A vector solves this problem by allocating
memory as needed.


Vector
// Demonstrate a vector.
#include <iostream>
#include <vector>
#include <cctype>
int main()
{
vector<char> v(10); // create a vector of length 10
int i;
// display original size of v
cout << "Size = " << v.size() << endl;
// assign the elements of the vector some values
for(i=0; i<10; i++) v[i] = i + 'a';
// display contents of vector
cout << "Current Contents:n";
for(i=0; i<v.size(); i++) cout << v[i] << " ";
cout << "nn";
cout << "Expanding vectorn";
/* put more values onto the end of the vector,
it will grow as needed */

for(i=0; i<10; i++) v.push_back(i + 10 + 'a');
// display current size of v
cout << "Size now = " << v.size() << endl;
// display contents of vector
cout << "Current contents:n";
cout << "nn";
// change contents of vector
for(i=0; i<v.size(); i++) v[i] = toupper(v[i]);
cout << "Modified Contents:n";
cout << endl;
return 0;
}


Accessing a Vector Through an
Iterator
int main()
{
vector<char> v(10); // create a vector of length 10
vector<char>::iterator p; // create an iterator
int i;
// assign elements in vector a value
p = v.begin();
i = 0;
while(p != v.end()) {
*p = i + 'a';
p++;
i++;
}


Do Practice


Function overloading

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