Pointer to an object in C++

In C++, pointers to an object allow us to reference and manipulate class objects using the memory addresses. It is an essential feature that is very helpful in dynamic memory allocation, passing objects to functions efficiently, implementing polymorphism, and working with data structures, such as linked lists and trees.

A pointer to an object in C++ is a variable that contains an object's memory address. Pointers provide indirect access to control over memory items. They are especially helpful when we need to dynamically allocate memory for objects, build linked lists or trees, or pass objects by reference to methods without making duplicates.

The behaviour of an object pointer is identical to that of a variable pointer. But in this case, the object's address is kept instead of the variables. When a class object is formed in the main function, a pointer variable is declared similarly to the variable itself. Using a data type for the pointer is not recommended when generating a pointer to an object. Instead, we must make use of the object pointer's class name. The -> symbol must be used to call a class member function using a Pointer in the main function.

Declaring a Pointer to an Object

We declare a pointer to an object using the object's class name followed by an asterisk (*) and the pointer name.

Creating Objects and Pointers

Objects are created using the new keyword, which dynamically allocates memory for the object. After that, the Pointer is assigned the memory address of the newly created object.

Accessing Object Members via Pointer

We can use the arrow operator (->) to access members (variables and functions) of the object through the pointer.

Dereferencing a Pointer

We "dereference" the pointer using the asterisk (*) operator to access the object itself (rather than its members).

Deleting Objects and Pointers

When we're done with the dynamically allocated object, which frees the memory using the delete keyword is important.

Null Pointers

Pointers can also hold a special value, nullptr, which indicates that they are not pointing to a valid memory address.

Passing Pointers to Functions

In C++, pointers are often used to pass objects by reference to functions, which allows the function to modify the original object.

Pointer Arithmetic

Pointer arithmetic applies to pointers to arrays but not necessarily to pointers to objects.

C++ Pointer to an Object Example

Let's take an example to understand the pointer to an object in C++.

Output:

Data: 42
Data: 42
Data: 99
Data: 0
Data: 10
Data: 20

Explanation:

In this example, we demonstrate how to work with pointers to objects, dynamic memory allocation, and object modification via pointers. After that, a class MyClass is defined with a constructor and a display() method. Finally, an object is dynamically created using a pointer, accessed, and modified via both dereferencing and a separate function.

An Array of Pointers to Objects

In C++, an array of pointers to objects can be created, which is especially useful to manage multiple objects efficiently. In C++, arrays use indices to access elements, which allows us to have random access to a collection of related data. These elements are typically stored in contiguous memory locations. Arrays can store basic data types, including int, float, double, and char, as well as pointers to more complex objects.

Syntax

It has the following syntax:

C++ Array of Pointers to Objects Example

Let us take an example to illustrate an array of pointers to objects in C++.

Output:

Title: Book 1
Title: Book 2

Explanation:

In this example, we dynamically create two Book objects, assign titles to them using a loop, and display their titles using a member function. Finally, it frees the allocated memory using delete to prevent memory leaks.

Dynamic Memory Allocation for Objects

In C++, dynamic memory allocation for objects is useful when the system cannot determine the number of objects at the time they are compiled. C++ uses the new operator to provide memory for an object and return a pointer to it.

C++ Dynamic Memory Allocation for Objects Example

Let us take an example to illustrate the dynamic memory allocation for objects in C++.

Output:

Name: Alice, Age: 25

Explanation

In this example, we have taken a Person object that is dynamically created using a pointer p. Memory for the object is allocated at runtime using new, and its members (name and age) are assigned values. After that, the display() function is called to print the data. Finally, delete is used to free the allocated memory, which prevents memory leaks.

Why is Dynamic Memory Allocation Helpful?

There are many scenarios in which dynamic allocation is needed.

• When the set of objects can change at compile time.
• To allow objects to be created at any time during a program's execution.
• In setting up dynamic data structures such as linked lists, trees and graphs.
• To reduce the memory used by the program and better manage when objects are created and destroyed.
• It makes it easier to scale the application and use less memory.

Accessing Object Members Through Pointers

When using dynamic allocation or pointers to point to objects, we can reach the member variables with the name of the pointer.

Alternatively, it can be written as:

However, using -> is preferred due to its simplicity and readability.

Base Class Pointers to Derived Class Objects

C++ allows polymorphism by using an object of a base class to point to an object of a derived class. Because of this, virtual functions can be called using dynamic method dispatch.

C++ Base Class Pointers to Derived Class Objects Example

Let us take an example to illustrate the base class pointers to derived class objects in C++.

Output:

Dog barks

Explanation:

In this example, we have taken an Animal-based class that has a virtual speak() function and also taken a Dog-derived class that overrides the speak() function. After that, in the main() function, an Animal* pointer (a) points to a derived Dog class (d).

Advantages of Pointer to Object in C++

Several advantages of a pointer to an object in C++ are as follows:

• It supports dynamic memory allocation, which makes the use of memory easier and more efficient.
• It supports runtime polymorphism, which helps set behaviour depending on what happens at the moment.
• It supports making dynamic data structures, including linked lists, trees, and graphs.
• It reduces the requirement to copy full objects when passing objects to functions.
• It enables objects to be created on the heap, which keeps them alive for longer than the function.

Challenges of Pointer to an Object in C++

Several challenges of pointer to an object in C++ are as follows:

• Even though pointers are powerful, using them improperly can cause mistakes.
• Common pitfalls include:
• Any dynamically allocated memory that goes unnoticed will eventually cause a memory leak.
• If we delete an object and try to use the memory it occupies, we get a dangling pointer error.
• Dereferencing, accessing, and null pointers can make a program crash at runtime.

Conclusion

In C++, a pointer to an object performs an essential role to allow dynamic behavior, memory efficiency, and the implementation of object-oriented design principles. It offers important features, including runtime polymorphism and dynamic object management. However, their utilization needs careful handling to prevent common pitfalls, such as memory leaks and dangling pointers. Developers can make C++ applications more flexible and efficient by learning how to use object pointers.

C++ Pointer to an Object MCQs

1) What will occur if you allocate new memory for an object but never delete it?

1. The program leads to an immediate crash
2. At the end, the object is automatically removed.
3. A memory leak will occur
4. An object remains at rest in this case.

2) Which of the following is a common pitfall when using pointers to objects?

1. Using the delete keyword more than once for the same pointer
2. Applying the arrow operator
3. Employing dynamic memory
4. Selecting private members

3) What is the proper description of how a pointer to a base class is related to an object of a derived class?

1. It is not possible for a base class pointer to point at something of a derived class
2. A base class pointer can point to a derived class object and call only base class methods unless virtual functions are used
3. Normally, a base class pointer invokes functions defined in the derived classes.
4. You must convert a base pointer to a derived class using explicit casting.

4) Why do we usually assign a base class pointer to a derived class object in C++?

1. To decrease the amount of memory used
2. To ensure there is no need for virtual functions
3. To enable runtime polymorphism through virtual functions
4. Allow base class methods to be called only by derived classes

5) Consider the following code snippet. What will be the output?

1. Compilation error
2. No output
3. Runtime error
4. Demo::show()