Difference between Structure and Class in C++

Key Differences Between Structure and Class in C++

A structure is a user-defined data type that groups logically related data items, whereas a class is a blueprint used to create specific types of objects.
In C++, both structures and classes support user-defined constructors and destructors.
The primary difference is that structure members are public by default, while class members are private by default.
Both can support inheritance, polymorphism, and encapsulation.
Structures are often used for simple data grouping; classes are preferred for complex behaviors and designs.
Memory allocation (stack or heap) depends on how objects are declared, not on whether they are classes or structures.
Member variables can be initialized directly inside both structures and classes in modern C++.

What is the Structure in C++?

Structure is a user-defined data type that combines logically related data items of different data types like float, char, int, etc., together.

All the structure elements are stored at contiguous memory locations. Structure type variable helps you store more than one data item of varying data types under one name.

Syntax of Structure in C++

Here is a syntax of Structure:

struct struct_name
{
// struct data members
}

In the above syntax, the struct keyword is used. The struct_name is the name of the structure. The struct members are added within curly braces. These members probably belong to different data types.

What is Class in C++?

Class is a blueprint or a set of instructions to build a specific type of object. It is a basic concept of Object-Oriented Programming which revolves around real-life entities. Class in a programming language determines how an object will behave and what the object will contain.

Class is also a user-defined data type which can have different kinds of data types and member functions inside its body.

Syntax of Class in C++

Here is a syntax of Class:

class class-name
{
// data
// functions
};

In the above syntax, the class name is the name that is assigned to the class. The data is the member of the class, normally declared as variables. The functions here are the class functions.

Structure vs Class in C++

Here is the main difference between Structure and Class in C++:

Structure	Class
A structure is a user-defined data type that groups related variables.	A class is a user-defined data type that acts as a blueprint for objects.
Declared using the `struct` keyword.	Declared using the `class` keyword.
Default access specifier is public.	Default access specifier is private.
Supports member functions, constructors, destructors, and inheritance just like classes.	Fully supports OOP features like constructors, destructors, inheritance, polymorphism.
Members can be private or protected if explicitly declared.	Same here—access control is fully supported.
In C++, structs and classes are almost identical, except for the default access specifier.	Same capabilities; only the default access specifier differs.
Used often for plain data structures (POD: Plain Old Data).	Used often for full OOP design.
Instances are typically referred to as “structure variables” informally.	Instances are called objects.

Which One Should You Choose?

If you have a large memory footprint or like to use a concept like inheritance, then you can choose a class. On the other hand, the structure can be used when you have a small memory field or footprint that is needed to initialize default values.

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