Understanding The Difference Between Structure And Class In C++

Introduction

While coding in C++ we have come across both of these terms and we might have also used them interchangeably. Structure and Class in C++ are quite similar to refer to and most of the time we fail to understand the difference between them and mistakenly use either of them without any particular thought.

Structure as we all know is a user-defined data type used in C/C++ to group a large variety of data types together. Well, a class does the same thing in C++ but with more features like allowing defining of methods/functions inside them.

Yes, as you would already know, class is a concept described and included in C++ but not in C as C is a procedural language and has less to no focus on data or objects.

C++ being an object-oriented programming language has more focus on data and its manipulations. Although that’s not it, there are certainly more differences that we will put out for you to make this difference between structure and class in C++ more clear.

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Definitions and Declarations

Let’s start with defining these two data structures:

Structure: A struc data structure is a user-defined type that is used to store multiple types of data. It groups together multiple data types and forms a single data type from those. It is generally considered a variable.

Class: A class is the building block of an Object-Oriented programming language. It is a user-defined data type that holds its own data members and member functions that can be accessed and used by creating an instance of that class. A C++ class is considered a blueprint for an object.

Also read about Difference Between C & C++ Programming Languages

Applications and Examples

Structure 

Let’s get started with a general syntax and examples of each. Structures, as we know, have been around from C language and as C is a procedural programming language that has less focus on data, thus structures can only store member variables and not functions.

These member variables are by default public. This also placed a problem for security issues as the members can be easily modified.

Syntax:

 struct CodingNinjas{
    string Course; 
    Int numberofhours;
    string placement;
};

By default, these members are public and can be accessed by creating a normal variable of structure CodingNinjas along with a dot(.) operator.

Example:

int main()
{
struct CodingNinjas c;  // The variable c is declared like a normal variable
	c.Course = “C++ foundation”;
	c.numberofhours = 10;
	c.placement = “guranteed”;

	cout<<c.Course<<”\n”;
} 

Output: C++ foundation

Class

In a similar way, we can define a class and store not only multiple types of data variables but also functions. The class was designed to support the object-oriented design paradigm and to provide much more functionality than structures. To access the members of a class one has to create an instance of the class called object. This object is used to access the member functions and variables of the class.

Syntax:

class CodingNinjas
{
    // Access specifier
    public:
 
    // Data Members
    string course;
 
    // Member Functions()
    void courseprint()
    {
       cout << "Course name is: " << course;
    }
};

Example:

int main() {
 
    // Declare an object of class geeks
    CodingNinjas c;
 
    // accessing data member
    c.course = "C++ foundation";
 
    // accessing member function
    c.courseprint();
    return 0;
}

Output: Course name is: C++ foundation

Features of classes over structures

• Classes have access specifiers that provide better control over the accessibility of data members. This provides more security with private, protected, and public specifiers so that we can assign out members whichever specifier is required according to the need. This is one of the major differences between structure and class in c++. Let me explain this briefly, we have three access specifiers
  • Private: The class members declared with a Private modifier can be accessed only by the member functions inside the class. They cannot be accessed directly by any object or function outside the class. Member functions or friend functions are allowed to access the private members of the class. Objects cannot directly access these data members.
  • Protected: Protected access modifier is the same as private access modifier in the way that it can not be accessed outside of the class in which they are defined unless, with the use of a friend class, the difference is that the class members declared as Protected can be accessed by any subclass(derived class) of that class as well.
  • Public: All the class members associated with the public specifier will be available to everyone. Any object can directly access these members.

Also Read about Understanding the Differences Between C++ and C#

This is one of the major differences between structure and class in C++.

• As we know polymorphism and inheritance are concepts developed for object-oriented programming design, hence structures do not support these concepts. Polymorphism and inheritance also introduce the ability to reuse components and classes rather than defining them again and again. This is supported by Class in C++. Classes in C++ support compile time and run time polymorphism and various types of inheritance abilities like multilevel, multiple, etc.
  • Structures do not support the use of functions inside them and hence it is not possible to declare or override functions inside them thus do not support polymorphism.
  • The concept of inheritance is dependent upon the access specifiers and structures in C++ do not support them.

• Constructors and Destructors are important member functions that are called by the compiler when an object of a class is being instantiated. These are simple functions present inside a class by default or can be user-defined. Being functions again are not supported by structures.  

• The most basic struct vs class difference comes in the ability to handle null values. Structures do not have the ability to allow null values whereas a class can be given null values, this comes from the fact that a structure is considered as a variable.

Difference between Structure and Class in C++

Comparison Criteria	Structure	Class
Definition	Structure groups together multiple data types and it is considered as a structure variable.	Class combines multiple data types into one group and its object is considered as an instance of a class.
Declaration	struct  name {Data_type var1;Data_type var2;Data_type var3;…}	class name {Data_type var1;Data_member function(){}}
Nature	Value type variable	Can be accessed using reference
Memory Allocation	Structures are stored in stack memory	Class is stored in Heap memory
Null value handling	Structures do not allow null values	Class can have null values
Constructor & destructor	Structures do not have the possibility for constructors and destructors	Classes do have constructors and destructors by default, we can also declare user-defined constructors also.
Polymorphism and Inheritance concept	Structures do not support Polymorphism & inheritance	Classes extensively support polymorphism and inheritance. It was developed to allow object-oriented design paradigms.
Access Specifier	By default all the member variables in the structure are public	Classes have member variables and functions by default private.

Structures and Classes are used very frequently interchangeably without understanding the real difference.  We tried to put the difference so that the next time you use structure or class you know which one specifically to use.

The concept of structures and classes is an important aspect of learning the C++ language in and out. There are subtle differences between class and structure and should be used according to the needs. The structure variable is an easy-to-use, user-defined data structure for simple tasks.

Whereas class gives more control of data and is used for more secure manipulation of data variables along with the support for functions.

Frequently Asked Questions

Key Takeaways

This blog tried to differentiate between structure and class in C++ and pointed out the basis for the difference. It started from basic definitions of both and following the features that made one more advantageous than the other. It also specifies each difference in a table format for easy reference and to make a side-by-side comparison of class and structure.

If you are interested in the practical experience of the concepts of class and structures you should checkout  CodeStudio – the best platform to practice Programming and prepare for coding interviews to practice problems related to classes and structures being applied to various problems. 

By Aniruddha Guin