Classes & Objects

Mr. Santosh N. Nagargoje

Class

• User defined data type which binds data and its functions together
• Blueprint for creating objects
• Defines properties and behaviour
• Syntax:

​

class class_Name{

access_specifier:

Member_variable declaration( properties)

access_specifier:

Member_function declaration/definition(Behaviour)

};

Access Specifiers

• public
• Data can be accessed from anywhere outside the class
• private
• Data cannot be accessed from outside the class.
• It can be accessed within the class only by using member functions.
• protected
• Data can only be accessed within the class and within the subclasses(child classes)

Class Example

class Person{

private:

string name;

int age;

double salary;

char gender[5];

public:

void getInput();

void putOutput();

};

Member Variables

Member functions

(can be defined inside the class or outside class)

Object

• Instance of a class
• After object creation(instantiation), memory will be allocated.
• Syntax:

​

• Example:

​

• Accessing Class Members:

​

​

​

Class_name Object_Name;

Person p1;

Object_name.member;

p1.getInput();

A Complete Example

class Person{

private:

string name;

int age;

public:

void getInput();

void putOutput()

};

void Person::getInput(){

cin>>name;

cin>>age;

}

​

void Person::putOutput(){

cout<<name;

cout<<age;

}

int main(){

Person p1;

p1.getInput();

p1.putOutput();

return 0;

}

Static Members

• Static Member Variable
• Used to share same copy of data amongst all the objects.
• Syntax: static data_type identifier
• Example: static int count;
• Defining member: data_type class_name:: variable_name;
• Static Member Function:
• Access to only static members declared in the same class
• defined using static keyword
• Can be called using class name. ( class_name :: function_name )

Constructor

• Special member function which initializes objects.
• Its name is the same as the class name.
• Invokes automatically at the time of object creation.
• Should be declared in the public section
• Do no have return types
• Cannot be inherited
• Makes implicit call the new and delete operators

​

Default Constructor

• Accepts no parameters
• If not defined compiler by default provides it.
• Syntax:

​

class class_Name{

member variable;

public:

class_name(){ //default constructor

//member variable initialization

}

};

Parameterized Constructor

• Take arguments
• Used to initialize every object with different set of values.
• Syntax:

​

​

​

• How to Call:
• class_name object_name(para1,para2);
• class_name object_name = class_name(para1,para2);

​

​

class class_Name{

member variable;

public:

class_name(para1,para2){ //parameterized constructor

//member variable initialization

}

};

Copy Constructor

• initializes an object using another object of the same class.
• Syntax:

​

class class_Name{

member_variable;

public:

class_name(const class_name &old_obj){ //parameterized constructor

member_variable=old_obj.member_variable;

}

};

​

class_name new_obj = old_obj; //invoking copy constructor

Destructors

• member function which destructs or deletes an object.
• called automatically when the object goes out of scope.
• have same name as the class preceded by a tilde (~).
• Does not have return type.
• Syntax:

~class_name();

Inline Function

• Function with inline keyword
• compiler places a copy of the code of that function at each point where the function is called at compile time.
• Syntax:

​

inline return_type class_name :: function_name(){��}