UNIT III C++ Notes.pdf

UNIT III In C++, a constructor is a special member function of a class that is automatically called when an object of that class is created. The purpose of a constructor is to initialize the object’s data members with default or user provided values. Key...

UNIT III In C++, a constructor is a special member function of a class that is automatically called when an object of that class is created. The purpose of a constructor is to initialize the object’s data members with default or user provided values. Key Features of Constructors: 1. Same Name as Class: The constructor has the same name as the class. 2. No Return Type: Constructors do not have a return type, not even void. 3. Called Automatically: The constructor is called automatically when an object is created. Types of Constructors: 1. Default Constructor: A constructor that takes no parameters. 2. Parameterized Constructor: A constructor that takes parameters to initialize the object with userprovided values. 3. Copy Constructor: A constructor that creates a new object as a copy of an existing object. Types of Constructors in C++ In C++, constructors are special member functions used to initialize objects. They ensure that the object is properly set up before it is used. The language supports several types of constructors, each designed for different scenarios of object initialization. 1. Default Constructor A default constructor is a constructor that takes no arguments or has default values for all its parameters. If no constructor is explicitly defined by the programmer, C++ automatically provides a default constructor that initializes basic data members to their default values (like `0` for integers). Ensures that objects are created with valid initial states, even when no specific values are provided. Supports the creation of arrays of objects, as default constructors are called for each element. Advantages: Automatically provided by the compiler if not explicitly defined. Useful for initializing objects to a consistent default state. 2. Parameterized Constructor A parameterized constructor allows you to pass arguments when creating an object, enabling the initialization of objects with specific values. It requires the programmer to define the parameters and initialize the object’s data members based on those values. Provides flexibility to initialize objects with custom values. Facilitates better control over object creation and initialization. Advantages: Avoids the need for setters or additional methods to initialize objects after creation. Allows initializing different objects with different values at the time of creation. 3. Copy Constructor A copy constructor is used to create a new object as an exact copy of an existing object. It is called when an object is passed by value, returned from a function, or explicitly copied. If not defined, the compiler generates a default copy constructor that performs a shallow copy (bitwise copy). Used in scenarios where objects need to be duplicated, ensuring that an exact copy is made. Essential in managing dynamic memory to prevent issues like double deletion, which occurs when two objects share the same memory. Advantages: Helps in deep copying when the object has dynamically allocated resources (like memory or file handles), ensuring proper resource management. Custom copy constructors allow for deep copy, avoiding the pitfalls of shallow copying. 4. Dynamic Constructor A dynamic constructor involves allocating memory dynamically at runtime using operators like `new` within the constructor. Typically used when objects require memory allocation that cannot be determined at compile time. Efficient use of memory since the exact amount needed is allocated at runtime. Allows creating objects that can manage varying amounts of resources. Advantages: Flexibility in memory management since memory can be allocated and managed dynamically as required. Suitable for handling large data structures or when the exact size of an object is not known during compilation. 5. Default Arguments Constructor A default arguments constructor allows the programmer to provide default values for some or all of the constructor’s parameters. This means that the constructor can be called with or without arguments, depending on the situation. Reduces the need for multiple constructors with different numbers of parameters. Provides flexibility by allowing the same constructor to be used for both default and parameterized initialization. Advantages: Simplifies code by reducing the number of overloaded constructors required. Combines the benefits of default and parameterized constructors, offering flexibility in object creation. Benefits of Using Constructors in C++: 1. Automatic Initialization: Constructors ensure that objects are automatically initialized upon creation, avoiding uninitialized variables or undefined states. 2. Encapsulation: Constructors help encapsulate the initialization logic within the class, reducing the need for external initialization functions. 3. Overloading Support: Multiple constructors can be defined (constructor overloading), allowing flexibility in object initialization based on different use cases. 4. Resource Management: Constructors, combined with destructors, allow for effective resource management (e.g., dynamic memory allocation), making object-oriented programming more robust. 5. Code Reusability: Constructor overloading allows the creation of objects in various ways without needing separate functions for each case, increasing code reusability. Constructor Overloading: C++ supports constructor overloading, where multiple constructors can be defined with different parameters, allowing object initialization in various ways. Dynamic Initialization of Objects Dynamic initialization of objects refers to the process of initializing an object at runtime, rather than at compile time, by using values that are only available during the program's execution. This is typically achieved through dynamic memory allocation or by computing values at runtime. Dynamic initialization is useful in situations where the exact values required to initialize an object are not known beforehand, and they can only be determined while the program is running. Destructor: A destructor is the opposite of a constructor, used to clean up when an object is destroyed, and it has a ~ symbol before the class name. A destructor in C++ is a special member function of a class that is automatically invoked when an object is destroyed. Its primary purpose is to free any resources (such as memory, files, or database connections) that were acquired during the lifetime of the object. Destructors ensure that when an object is no longer needed, the resources it holds are properly released, avoiding memory leaks and other resource mismanagement issues. Characteristics of Destructors:  1. Same Name as Class: A destructor has the same name as the class but is prefixed with a tilde (~). For example, for a class MyClass, the destructor would be ~MyClass(). 2. No Parameters: Destructors do not take any arguments, nor do they return any values. This is because they are automatically invoked by the compiler when the object’s lifetime ends. 3. Automatically Called: Destructors are automatically called when an object goes out of scope or is explicitly deleted (in case of dynamically allocated objects). 4. One Per Class: There can only be one destructor per class, as destructor overloading is not allowed in C++. 5. No Explicit Invocation: Unlike other member functions, destructors cannot be called explicitly by the programmer; they are invoked implicitly by the compiler. 6. Order of Destruction: If an object is composed of multiple components (such as other objects), the destructor destroys these components in reverse order of their initialization. Difference Between Constructor and Destructor In C++, constructors and destructors are special member functions of a class, but they serve opposite purposes. S.No Feature Constructor Destructor 1 Purpose Initializes an object when it is Cleans up and releases resources created. when an object is destroyed. 2 Name Has the same name as the class, Has the same name as the class. but preceded by a tilde ~. 3 Return Type No return type, not even void. No return type, not even void. Can be overloaded to accept 4 Parameters Cannot be overloaded; no parameters (parameterized parameters. constructors). Automatically called when an 5 Call Automatically called when an object goes out of scope or is object is created. explicitly deleted. Multiple A class can have multiple 6 A class can have only one constructors (constructor Instances destructor. overloading). 7 Default If not defined, the compiler If not defined, the compiler provides a default constructor. provides a default destructor. Typically used to allocate Typically used to release 8 Use Case resources, initialize variables, resources, close files, or clean up or set up the object. memory.