C++ Classes and Objects
C++ Classes/Objects
C++ is an object-oriented programming language.
Everything in C++ is associated with classes and objects, along with its attributes and methods. For example, in real life, a car is an object. The car has attributes, such as weight and color, and methods, such as drive and brake.
Attributes and methods are basically variables and functions that belong to the class. These are often referred to as "class members".
A class is a user-defined data type that we can use in our program, and it works as an object constructor, or a "blueprint" for creating objects.
Create a Class
To create a class, use the class keyword:
Example
Create a class called "MyClass":
class MyClass { // The class
public: // Access specifier
int myNum; // Attribute (int variable)
string myString; // Attribute (string variable)
};
Example explained
- The
classkeyword is used to create a class calledMyClass. - The
publickeyword is an access specifier, which specifies that members (attributes and methods) of the class are accessible from outside the class. You will learn more about access specifiers later. - Inside the class, there is an integer variable
myNumand a string variablemyString. When variables are declared within a class, they are called attributes. - At last, end the class definition with a semicolon
;.
What's the difference between a Class and a Structure?
The example above looks much like a structure (struct).
- Structures are much simpler than objects. Unlike objects, structures cannot do encapsulation, inheritance or polymorphism, which you will learn more about in the next chapters. If all you need is a collection of variables, a structure is easier to use than an object.
Create an Object
In C++, an object is created from a class. We have already created the class named MyClass, so now we can use this to create objects.
To create an object of MyClass, specify the class name, followed by the object name.
To access the class attributes (myNum and myString), use the dot syntax (.) on the object:
Example
Create an object called "myObj" and access the attributes:
class MyClass { // The class
public: // Access specifier
int myNum; // Attribute (int variable)
string myString; // Attribute (string variable)
};
int main() {
MyClass myObj; // Create an object of MyClass
// Access attributes and set values
myObj.myNum = 15;
myObj.myString = "Some text";
// Print attribute values
cout << myObj.myNum << "\n";
cout << myObj.myString;
return 0;
}
Try it Yourself »
Multiple Objects
You can create multiple objects of one class:
Example
// Create a Car class with some attributes
class Car {
public:
string brand;
string model;
int year;
};
int main() {
// Create an object of Car
Car carObj1;
carObj1.brand = "BMW";
carObj1.model = "X5";
carObj1.year = 1999;
// Create another object of Car
Car carObj2;
carObj2.brand = "Ford";
carObj2.model = "Mustang";
carObj2.year = 1969;
// Print attribute values
cout << carObj1.brand << " " << carObj1.model << " " << carObj1.year << "\n";
cout << carObj2.brand << " " << carObj2.model << " " << carObj2.year << "\n";
return 0;
}
Try it Yourself »
