Reputation:

What is a Class and Object in C++?

Can we say that a Class is an Object?

Upvotes: 15

Answers (21)

Tabzo

Reputation: 1

In object-oriented programming , a class is a template definition of the method s and variable s in a particular kind of object . ... Subclasses can also define their own methods and variables that are not part of their superclass. The structure of a class and its subclasses is called the class hierarchy.

Upvotes: 0

Nitesh

Reputation: 315

No,class is not a object.

A class is a data type and object is the variable(instance) of class data type.

Upvotes: 1

user88637

Reputation: 12140

I will try to give more technical explanation rather than an abstract one. I think that definitions like "a class is a blueprint and an object is something made from this blueprint" are impossible to understand for newbies simply because these kind of definitions are abstract and context-less.

Classes and objects have a pure abstract meaning in the object oriented world but for simplicity I will reduce the definition to a more practical one.

Consider the following statement:

int a;

"int" is a type and is "a" is a variable which has the type "int".

C++ provides various ways to let the programmer define new types; for example:

typedef int* int_ptr;
int_ptr a;

In this example , a new type is defined int_ptr. "int_ptr" is a type , "a" is a variable which has the type "int_ptr". Another example:

struct Point
{   
    int x;
    int y;
};
Point a;

Here, a new type is defined, "Point", and "a" is a variable which has the type "Point".

So what is a class in C++? A class is another way to define a new type, just like the other ways mentioned above.

What is an object? An object is a variable which has a type that was defined using the class keyword.

For example:

class SmartPoint
{
public:
   Point(x,y);
   Move(x,y);
protected:
   int x,y ;
};

SmartPoint a;

In this example, a new type is defined, "SmartPoint", and "a" is a variable which has the type "SmartPoint".

You may ask then what is different between a type defined by using the "class" keyword or "struct" keyword or "typedef" — but that is a matter for another discussion.

Upvotes: 6

CodeFusionMobile

Reputation: 15110

A Class is like a blueprint, an object is like a house built from that blueprint.

You can have many houses with the same layout/floorplan (read class), but each is it's own instance (read object). Each has it's own owner, furniture, etc.

Note that there are also objects whose blueprint is not a class (e.g. integers).

Upvotes: 52

Sriram

Reputation: 1

Object is an data or a function which has an adress in run time memory and are also called as instances of class . Thus object is an class type variable or entity of c++ programming language.

Upvotes: 0

Surya

Reputation: 171

Here is an anology.
we have a classification called vehicles. Each vehicle will have some properties like :

seating capacity
fuel capacity
fuel consumption
type of transmission

Car, bike, truck, are some instances of vehicles. Each may have different set of properties.
Here vehicles is a class and all the properties are it's members and car, bike, truck are objects of the class vehicles.

Upvotes: 1

Jayraj Srikriti Naidu

Reputation: 99

A class is a logical construct while object is its physical copy.

A class can be thought of as a mould from which multiple objects are created which appear identical to the class

Objects can be thought of as carbon copies of the class. A perfect example of inheritance principle.

A class can be thought of as a parent of its children - objects

Upvotes: 0

Rohit Hajare

Reputation: 135

Class is collection of data and functions,its user defined data type.Class is specification for object.So you can say that object is variable for class or object is instance of class.

Upvotes: 0

Muhammed Thanveer Danish Melay

Reputation: 1

When you define a class, you define a blueprint for a data type. This doesn't actually define any data, but it does define what the class name means, that is, what an object of the class will consist of and what operations can be performed on such an object.

A class definition starts with the keyword class followed by the class name; and the class body, enclosed by a pair of curly braces. A class definition must be followed either by a semicolon or a list of declarations. For example, we defined the Box data type using the keyword class as follows:

class Box
{
   public:
      double length;   // Length of a box
      double breadth;  // Breadth of a box
      double height;   // Height of a box
};

The keyword public determines the access attributes of the members of the class that follow it. A public member can be accessed from outside the class anywhere within the scope of the class object. You can also specify the members of a class as private or protected which we will discuss in a sub-section.

Upvotes: -1

Aftab

Reputation: 1

Class is a collection of data member and member function.

Class is a user define data type.

Object is a class type variable.

Objects are also called instance of the class.

Each object contains all members(variables and functions) declared in the class. We can access any data member or member function from object of that class using . operator.

Upvotes: 1

ttchong

Reputation: 317

A class is not an object.

In simpler C language, a class is like a struct type, but more complex. Using a C struct example as analogy:

struct class_ {
    int attribute00;
    float attribute02;
    ...
}

struct class_ object_ = {0, 0.0, ...};

struct class_ is act like a class and object_ is act like an object. struct class_ has no physical storage in memory, object_ has physical storage in memory.

In human language, a word 'house' (as class) can defined in dictionary as place to stay, with doors, with windows, and rooms that you can only speak with your mouth to tell other people what is a house. A physical house (as object) is a solid build house on a land that you can move in and stay with your family.

A word 'house' take no physical occupation of land or space. A physical house occupy land and space.

Upvotes: 0

user75690

Reputation:

No, an object is an instance of a class...

Unless...

If you are implementing a software design tool that allows you to represent classes, interfaces, properties, inheritance, associations, aggregations, etc., then at runtime, yes, each class you place in the designer will be an object instance of the Class class. Ok, couldn't help myself finding an example so twisted and meta.

Now seriously, a class is not an object.

Upvotes: 2

Aidan

Reputation: 41

Class: A class defines a particular type's behaviours and properties.

Object: An object is an instance of a class.

For example, if you have a Dog named Bingo.

Dog would be the class defining its behaviours and properties
Bingo would be an object that is an instance of the Dog class

Strictly speaking, a Class is not an Object in C++. But in languages such as C# and Java that supports reflection, classes can be used like objects but that is a more advance topic and probaly not what the original question is asking.

Upvotes: 0

HerrHongo

Reputation:

Short Answer: In Languages C++, Java: No. In Languages like Python: Yes

Upvotes: -1

Georg Schölly

Reputation: 126105

Both classes and instances are objects, but object oriented programming doesn't force the language to have classes & instances.

Upvotes: -2

Nick Dandoulakis

Reputation: 43110

In C++, Objects are essentially the variables and Classes are the types of their values.

Upvotes: -1

Pete Kirkham

Reputation: 49311

C++ supports many paradigms, but not the 'everything is an object' style of object-oriented programming. Classes exist in the source code, but do not exist at run time. Even runtime type information doesn't preserve Classes as object, but only provides a capability to get opaque ids which correspond to the type.

Upvotes: 0