Difference Between Structure and Class in C++

1. the struct vs. class Keywords in C++
2. Access Modifiers in class vs. struct in C++
3. Memory Allocation in class vs. struct in C++
4. Null Values in class vs. struct in C++
5. Value Type vs. Reference Type in class vs. struct in C++
6. Security in class vs. struct in C++

This article explains the difference between a structure and a class in C++. This article is written concerning the latest version of C++; there were many more restrictions and differences between a struct and a class in the old versions.

In most cases, the structure is quite similar to a class, but few differences. Let’s look at them one by one.

the struct vs. class Keywords in C++

A structure is declared using the struct keyword, whereas the class keyword is used to declare a class.

The syntax for a class:

class demo {
 private:
 private
  members...
      .

      public : public members....
};

The syntax for a structure:

struct demo {
  members1;
  members2;
  ...
};

Access Modifiers in class vs. struct in C++

The class and struct in C++ have three access specifiers public, private, and protected, but in C++, members of a structure are public by default, and members of a class are private by default.

Example code using class:

#include <bits/stdc++.h>
using namespace std;

class demo {
  int temp;
};

int main() {
  demo d;
  d.temp = 20;
}

Output: We get a compile error because the temp is private.

[Error] int demo::temp is private
[Error] within this context

Example code using struct:

#include <bits/stdc++.h>
using namespace std;

struct demo {
  int temp;
};

int main() {
  demo d;
  d.temp = 20;
  cout << d.temp;
}

Output:

20

Memory Allocation in class vs. struct in C++

Whenever a structure is created and implemented, memory is allocated in the stack area, but memory is allocated in the heap area when a class is created and implemented.

Null Values in class vs. struct in C++

Members of structure cannot be null values, whereas class members can have null values.

Value Type vs. Reference Type in class vs. struct in C++

In C++, Structures are a value type, and Classes are a reference type. Value types store their content on a stack, and they directly hold the value where they are declared, so whenever a struct variable is created, the variable directly contains the data of the struct.

But in the case of a class of reference type, whenever an object is created, it holds the reference to it instead of the data.

Security in class vs. struct in C++

Security is a major issue concern with structures because we cannot hide the end-users implementation details, but design details can easily be hidden in class implementation.

Let’s summarize the differences in a tabular form.