Constructor in C++: Types, Features, Syntax, & More

Almost all object-oriented programming languages, including Java, C#, C++, and Python, employ constructors. Constructors are essential for object-oriented programming because they allow programmers to initialize objects before using them. They also help create new instances of objects with certain features and can be used to initialize variables with default values and other initialization-related tasks. 

For example, the Employee class constructor can have three arguments: the employee’s name, salary, and age. Default values for an object’s data members can also be defined using constructors. Finally, constructors can be used to generate extra objects or connect to outside services. In this blog, we will learn what are constructors in C++, their types, features, and more.

Understanding Constructors in C++

A constructor is a particular member function of a class that is called automatically when an object of that class is created in C++. Its function is to initialize the data members of the object or to conduct any other setup operations. The constructor is in charge of allocating memory and setting the object’s state

For example,

class MyClass {
public:
    // Constructor
    MyClass() {
        // Initialize data members or perform setup tasks
    }
};

Here, ‘MyClass’ has a default constructor that accepts no parameters. When a ‘MyClass’ object is created, the constructor is immediately invoked. A class can have several constructors, each with its own set of arguments. This enables you to build things with varied beginning states or give different object construction methods. Constructors are critical in object-oriented programming because they guarantee that objects are correctly initialized before usage. You can learn more about this by taking an online programming with C and C++ course.

Categories of Constructors

Constructors offer a complete framework for generating and initializing objects in C++ by merging object initialization and memory allocation operations.

Constructors in C++ are divided into two categories:

1. Object Initialization

Constructors are in charge of initializing an object’s data members. They define the object’s initial state by assigning values to its member variables and guarantee that an object is legitimate and usable when it is created.

2. Memory Allocation

Constructors are engaged in the process of allocating memory to objects. They are responsible for allocating memory to hold an object’s data when it is formed. They also conduct memory allocation duties, including dynamic memory allocation to guarantee that the object has enough memory space.

8 Different Types of Constructors in C++

Constructors come in many different forms and sizes in C++. Here are the different types of constructors in C++:

1. Copy Constructors

By duplicating the values of an existing object of the same class, copy constructors create new objects. They are often used when you wish to make a copy of an existing object and generate a new one.

2. Conversion Constructors

They are a type of dynamic constructor that lets you create objects via dynamic memory allocation. They can be used to dynamically initialize the member variables of the object and allocate memory for it.

3. Variadic Constructors

You can create objects with a varying number of inputs using variadic constructors. This means that each time you create an instance of the class, you might pass a different amount of arguments. When you need flexibility in the number of parameters required to create an object, these constructors can be helpful.

4. Default Constructor

 A constructor that accepts no parameters is said to be the default. If no additional constructors are defined, the compiler will automatically generate it. The default constructor sets the members to their default initializers or initializes the object with default values.

5. Parameterized Constructor

A constructor that accepts one or more parameters is known as a parameterized constructor. When creating an object, you can use it to initialize the member variables with certain values. You can customize the object’s initial state by using this kind of constructor.

6. Move Constructor

An rvalue (temporary) object’s resources can be quickly transferred to a new object using the move constructor, a special constructor that was first introduced in C++. It is utilized in move semantics, which enables more effective data transfer, such as when functions return objects or when containers need to be resized.

7. Explicit Constructor

A constructor that bears the explicit keyword is said to be explicit. Implicit conversions during object initialization are avoided. It is frequently employed to ensure explicit object formation and prevent unintentional type conversions.

8. Parameterized Constructors

Constructors have a fixed number of arguments. When designing a constructor, you must define the parameters that are needed to initialize the member variables of the object. It is possible to build objects with defined beginning values using parameterized constructors.

Features of Constructor

Here are the features of constructors in C++:

• Object Initialization: A constructor’s main function is to initialize an object’s state at creation. It establishes the object’s initial values and allots memory to it.
• Same Name as Class: The constructors have the same name as the class to which they belong. They can be distinguished by the fact that they do not have a return type, not even void.
• Automatic Invocation: When the new keyword is used to create an object of the class, constructors are immediately called. Before an object is utilized, they make sure it is in a usable state.
• Overloading: Constructors can be overloaded, allowing you to declare numerous constructors with distinct argument lists within a single class. This enables the creation of objects with various beginning states based on the supplied inputs.
• Default Constructor: A default constructor is automatically given by the compiler if a class doesn’t explicitly declare one. It either sets the members to their default initializers or initializes the object with default values.
• Parameterized Constructors: Constructors with parameters take arguments to initialize the member variables of the object. When creating an object, these arguments are used to give precise values to the object’s properties.
• Chaining Constructors: This keyword can be used to call another constructor from the same class in a chain of constructors. This makes it possible to reuse code and reduces the need for extra initialization of code.
• Initialization Order: Constructors run in a particular order. Prior to the derived class constructor, the base class constructor is called. The constructor of a class initializes instance variables in the order in which they are declared.
• Inheritance: A derived class first calls the constructor of its base class to initialize the inherited members when it is formed.
• Constructor Overriding: Constructors cannot be overridden in the majority of object-oriented programming languages, unlike normal methods. However, the super keyword can be used in some languages to support constructor chaining.

C++ Constructor Syntax

In C++, writing a constructor has a fairly straightforward syntax. When an object is created, a constructor, a specific function, is invoked. The constructor’s syntax is as follows:

class ClassName {
public:
    // Constructor declaration
    ClassName(); // Default constructor
    ClassName(parameters); // Parameterized constructor
    
    // Other member functions and variables
};

For example,

class Rectangle {
private:
    int width;
    int height;

public:
    // Default constructor
    Rectangle() {
        width = 0;
        height = 0;
    }

    // Parameterized constructor
    Rectangle(int w, int h) {
        width = w;
        height = h;
    }

    // Other member functions and variables
};

In the above example, the Rectangle class has a default constructor that initializes the width and height to 0. It also has a parameterized constructor that takes two arguments (w and h) and initializes the width and height with the provided values.

Conclusion

Constructors in C++ provide a valuable capability to generate objects with unique characteristics and carry out initialization operations. They come in various forms, including default, copy, and dynamic constructors. C also supports constructor overloading, enabling the declaration of multiple constructors within a single class.

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