Array Of Objects In C++ | A Complete Guide To Creation (With Examples)

Arrays are fundamental data structures of fixed size that are used for storing and manipulating a collection of elements in C++. We also need to create arrays when dealing with complex data structures since they are capable of holding multiple instances of objects. In this article, we will learn about arrays of objects in C++, i.e., arrays that hold objects and their technical aspects.

We will cover various aspects of working with arrays of objects, their declaration, initialization, and different methods and techniques employed to work with an array of objects in C++ programming. We will explain these concepts with the help of detailed explanations and code examples. Anyone who wishes to write effective, efficient, and sophisticated C++ code must have a solid understanding of this powerful feature. So let's get started!

What Is An Object?

An object is an instance of a class in C++. It is a major part of the OOP paradigm, and it encapsulates data (attributes) and functions (methods) into a single entity. Objects are created using a class blueprint, which represents specific entities with their own state and behavior. They enable the principles of encapsulation, abstraction, and polymorphism and help us to interact with and manipulate data through well-defined interfaces. They are used to write reusable, readable, and modular code, which are essential to model real-world entities and implement complex systems.

What Is An Array Of Objects?

Arrays are fundamental data structures of fixed size that are used for storing and manipulating a collection of elements in C++. An array of objects in C++ is a sequential collection of objects of the same class type. Just as a regular array holds elements of a basic data type, an array of objects stores and manipulates multiple instances of a particular class. Each element of an array of objects represents an individual object which possesses its own attributes and methods.

Declaration Of Array Of Objects In C++

There are several ways to declare an array of class objects in C++. Given below are two different ways to declare an array of objects in C++, along with code examples and explanations.

Declaring An Array Of Objects In C++ In Separate Lines

The first method for declaration and initialization is to do both of these separately.

Code:

Output:

object 1
object 2
object 3
object 4
object 5

Explanation:

1. We begin by including the necessary header files such as <iostream>(for input from user and output) and use namespace std.
2. Define a simple class called MyClass with an integer private attribute and a public method named method. The index of each array element/ object in the array of objects is passed into the method(), and it prints the objects in numerical order.
3. Next, we define another public method called initialize() that will take an integer value as a parameter. This is used to initialize the objects to the required value.
4. In the main() function, we then declare an array of objects having 5 objects of type MyClass. We then initialize the objects in the size of array by using a for loop to iterate through the array and call initialize from each object to initialize the object.
5. We iterate through each object in the array and call method() from each object using a for loop by passing in the index as a parameter.

Time & Space Complexity: Both these are O(n), where n is the number of objects in the array.

Declaring An Array Of Objects In C++ In Single Line

In this method, we declare and initialize the array of objects in a single go or simultaneously. The code example below showcases how this must be done.

Code:

Output:

object 1
object 2
object 3
object 4
object 5

Explanation:

1. Include the necessary header files such as <iostream>(for input and output) and use namespace std;
2. Define a simple class called MyClass with a private integer attribute and a public method named method and a constructor that takes an int value as a parameter and initializes the data attribute to the value passed.
3. The index of each object in the array of objects is passed into the method(), and it prints the objects in numerical order.

4. In the main(), we initialize 5 objects of type MyClass by passing in the values to the constructor, which initializes the objects.
5. Iterate through each object in the array and call method() from each object using a for loop by passing in the index as a parameter.

Time complexity: O(n), where n is the number of objects in the array.
Space complexity: O(n), where n is the number of objects in the array

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Initializing Array Of Objects In C++

Other than the techniques mentioned above, there are several other techniques that are used in declaring and initializing arrays. Some of these methods are explained below with detailed examples.

Using The New Keyword

The new keyword in C++ enables dynamic memory allocation and object initialization. We dynamically allocate memory for an array of objects in C++ using this method. The size of the array is determined at runtime and can be stored in a single variable. Given below is an example to help you understand this method:

Code Example:

Output:

object 1
object 2
object 3
object 4
object 5

Explanation:

1. Include the necessary header files such as <iostream> for input and output and use namespace std.
2. Define a simple class called MyClass with a method named method. The index of each object in the array of objects is passed into the method(), and it prints the objects in numerical order.
3. Next, we declare a dynamically allocated pointer using the new keyword that points to the array of objects. This allocates the necessary memory to perform the required actions on the array of objects.
4. We then iterate through each object in the array and call the method from each object using a for loop by passing in the index as a parameter.
5. Don’t forget to free the dynamically allocated memory using delete[]. Not deleting dynamically allocated memory could cause memory leaks leading to severe problems, including program crashes.

Time complexity: O(n), where n is the number of objects in the array.
Space complexity: O(n), where n is the number of objects in the array

Using Function Calls To Declare & Initialize An Array Of Objects In C++

Function calls can be utilized to declare and initialize an array of objects in C++. We can invoke a function that returns an object and assign the returned values to the elements of the array. This method enables flexible initialization of an array of objects. It also allows customizable and flexible initialization of an array of objects in C++. Given below is an example to demonstrate how function calls can be used to initialize an array of objects.

Code example:

Output:

object 1
object 2
object 3
object 4
object 5

Explanation:

We begin the example above by including the necessary header files such as <iostream>(for input and output) and use namespace std.

1. Then the program defines a simple class called MyClass with an integer private member and a public method called initialize(). This method takes an integer data type (int) parameter and initializes the data attribute to the value passed into the function.
2. The MyClass also defines a public method named method(). The index of each object in the array of objects is passed into the method(), and it prints the objects in numerical order.
3. Create an array named array_of_objects to utilize the class and function.
4. Initialize all the objects by using a for loop to call initialize for each member of the array by passing in the index as a parameter. This initializes all objects to the required values.
5. Iterate through each object in the array using a for loop and call method() from each object.

Time complexity: O(n), where n is the number of objects in the array.
Space complexity: O(n), where n is the number of objects in the array

Using Vectors To Initialize An Array Of Objects In C++

The <vector> header in C++ provides us with a convenient and safe way for declaring and initializing an array of objects in C++. It belongs to the standard library, and it offers various utilities, such as dynamic size adjustment when working with an array of objects in C++. Here is an example to help you better understand this concept:

Code example:

Output:

object 1
object 2
object 3
object 4
object 5

Explanation:

1. Include the necessary header files such as <iostream> (for input and output) and <vector> (contains various useful classes and methods to implement vectors).
2. Define a simple class called MyClass with a method named method and a constructor that has an int value as a parameter. The index of each object in the array of objects is passed into the method(), and it prints the objects in numerical order
3. Create a vector that holds objects of type MyClass and is named array_of_objects.
4. Initialize all the objects by using push_back() to call constructors for each object while passing the index of each object. This is done by iterating through the vector using a for loop.
5. Iterate through each object in the array and call method() from each object.

Time complexity: O(n), where n is the number of objects in the array.
Space complexity: O(n), where n is the number of objects in the array

Using malloc() To Declare & Initialize Array Of Objects In C++

Malloc() is a C function that is used to dynamically allocate memory at runtime. It’s not recommended to use the function malloc to initialize an array of objects in C++, as it doesn’t involve invoking constructors or properly initializing objects. Therefore, it is highly recommended to use pointers and the new keyword, as explained in the article, to declare and initialize an array of objects in C++. However, given below is an example to show you how the code would look with malloc().

Code:

Output:

object 1
object 2
object 3
object 4
object 5

Explanation:

1. Include the necessary header files such as <iostream>(for input and output) and <cstdlib> for using malloc().
2. Define a simple class called MyClass with a method named method that prints the output.
3. Initialize a const int variable named Size, which will be the size of the array of objects.
4. Create an array of objects using malloc() by statically casting malloc() as a pointer to MyClass. This is done as malloc() doesn’t return a specific type. Also, note that malloc() doesn’t invoke constructors or destructors. Therefore, when initializing objects or raw pointers, the programmer must explicitly call constructors and destructors to avoid memory leaks and other errors.
5. Iterate through each object in the array and call the method from each object using a for loop.
6. Free the dynamically allocated memory using free(). Not deleting dynamically allocated memory could cause memory leaks leading to severe problems, including program crashes.

Time complexity: O(n), where n is the number of objects in the array.
Space complexity: O(n), where n is the number of objects in the array

Using Pointers To Declare & Initialize Array Of Objects In C++

We can declare and initialize an array of objects in C++ using pointers. Pointers are an efficient and effective way to declare and initialize an array of objects in C++. Given below is an example to help you better understand how pointers are used to declare and initialize an array of objects in C++:

Code:

Output:

object 1
object 2
object 3
object 4
object 5

Explanation:

1. Include the necessary header files, such as <iostream> for user input and output, and use namespace std.
2. Define a simple class called MyClass with a method named method. The index of each object in the array of objects is passed into the method(), and it prints the objects in numerical order.
3. Then in the main() function, we declare 5 objects of type MyClass.
4. Next, the program creates an array of objects that contains pointers to the 5 objects of MyClass that were declared previously.
5. Iterate through each object in the array and call method() from each object using a for loop.

Time complexity: O(n), where n is the number of objects in the array
Space complexity: O(n), where n is the number of objects in the array

Conclusion

In this article, we have explored in detail the concept of an array of objects in C++. We have covered various topics and technical aspects that are important in understanding and working with an array of objects in C++. From the basic definitions of objects and arrays of objects to the general techniques of declaring and initializing arrays of objects in C++ to exploring various other techniques that are used to declare and initialize an array of objects. By utilizing this awesome tool, we can effectively and efficiently manage and manipulate collections of objects in our programs.

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Frequently Asked Questions

Q. What is the concept of array of objects in C++?

Arrays are fundamental data structures of fixed size that are used for storing and manipulating a collection of elements in C++. An array of objects in C++ is a sequential collection of objects of the same class type. Just as a regular array holds elements of a built-in data type, an array of objects stores and manipulates multiple instances of a particular class.

Q. Can we declare and initialize an array of objects in C++ using pointers?

Yes, we can declare and initialize an array of objects in C++ using pointers. Pointers are an efficient and effective way to declare and initialize an array of objects in C++. The new keyword in C++ enables dynamic memory allocation and object initialization. We dynamically allocate memory for an array of objects in C++ using this method. The size of the array is determined at runtime and can be stored in a variable.

Q. How to initialize an array of objects in C++ using function calls?

Function calls can be utilized to declare and initialize an array of objects in C++. We can invoke a function that returns an object and assign the returned values to the individual elements of the array. We enable flexible initialization of an array of objects through this. This method allows customizable and flexible initialization of an array of objects in C++.

Q. How to utilize vectors for initializing an array of objects in C++?

The <vector> header in C++ provides us with a convenient and safe way for declaring and initializing an array of objects in C++. It belongs to the standard library, and it offers various utilities, such as dynamic size adjustment when working with an array of objects in C++.

Q. Can we use the malloc() function to dynamically allocate memory for an array of objects in C++?

Malloc() is a C function that is used to dynamically allocate contiguous memory locations at runtime. It’s not recommended to use the malloc function to initialize an array of objects in C++, as it doesn’t involve invoking constructors or properly initializing objects. Therefore, It is highly recommended to use pointers and the new keyword to declare and initialize an array of objects in C++.

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