Blog · C++ · 04 Jul 2026 · Hindi + English

Difference Between Structure and Class in C++

In C++ the ONLY real difference: struct members are public by default, class members are private by default. Everything else is identical — proof with code.

The surprising truth

In C++, struct and class are almost identical twins. Both can have member functions, constructors, destructors, inheritance — everything. The ONLY real difference: struct members are public by default, class members are private by default. That's it. Everything else you may have heard is about C's struct, not C++'s.

struct Point {
    int x;          // public by default - accessible directly
};

class Point2 {
    int x;          // private by default - NOT accessible directly
};

Point  p;  p.x  = 5;    // OK
Point2 q;  q.x  = 5;    // ERROR: 'x' is private

Proof: a struct doing everything a class does

#include <iostream>
using namespace std;

struct Student {                       // struct, not class!
    string name;
    int marks;

    Student(string n, int m) {         // constructor in a struct - valid!
        name = n; marks = m;
    }
    void display() {                   // member function - valid!
        cout << name << " scored " << marks << endl;
    }
};

int main() {
    Student s("Aman", 92);
    s.display();
    return 0;
}

Aman scored 92

Compiles and runs perfectly. If someone says "struct cannot have functions" — that is true for C, false for C++. Knowing this distinction clearly is exactly what interviewers check.

Second (smaller) difference: default inheritance

struct B1 : A { };      // means : PUBLIC A   (struct defaults public)
class  B2 : A { };      // means : PRIVATE A  (class defaults private)

Same rule, applied to inheritance: struct inherits publicly by default, class privately. In practice everyone writes public explicitly, so this rarely bites — but it completes the answer.

C struct vs C++ struct (where the confusion comes from)

Feature	C struct	C++ struct
Member functions	❌ No	✅ Yes
Constructors/destructors	❌ No	✅ Yes
Access specifiers	❌ No (all public)	✅ private/protected/public
Inheritance	❌ No	✅ Yes
Declaring a variable	`struct Point p;`	`Point p;` (struct word optional)

When do C++ programmers actually use struct?

struct — for plain data bundles with no rules to protect: a Point{x, y}, an RGB colour, a pair of values. "Everything open, come and use it."
class — when data has rules and must be protected behind functions: BankAccount, Student with validation. "Data locked, use the official doors."
Interview line: "Technically only default access differs; by convention, struct for passive data, class for objects with behaviour and invariants."

चौंकाने वाला सच

C++ में struct और class लगभग जुड़वां हैं. दोनों में member functions, constructors, destructors, inheritance — सब कुछ हो सकता है. इकलौता असली अंतर: struct के members default में public होते हैं, class के default में private. बस. बाकी जो कुछ सुना है वह C के struct की बात है, C++ के struct की नहीं.

struct Point {
    int x;          // default में public - directly accessible
};

class Point2 {
    int x;          // default में private - directly accessible NAHI
};

Point  p;  p.x  = 5;    // OK
Point2 q;  q.x  = 5;    // ERROR: 'x' is private

Proof: struct वह सब करते हुए जो class करती है

#include <iostream>
using namespace std;

struct Student {                       // struct, class नहीं!
    string name;
    int marks;

    Student(string n, int m) {         // struct में constructor - valid!
        name = n; marks = m;
    }
    void display() {                   // member function - valid!
        cout << name << " scored " << marks << endl;
    }
};

int main() {
    Student s("Aman", 92);
    s.display();
    return 0;
}

Aman scored 92

Perfectly compile और run होता है. कोई कहे "struct में functions नहीं हो सकते" — यह C के लिए सच है, C++ के लिए गलत. यही distinction साफ-साफ जानना interviewers check करते हैं.

दूसरा (छोटा) अंतर: default inheritance

struct B1 : A { };      // मतलब : PUBLIC A   (struct का default public)
class  B2 : A { };      // मतलब : PRIVATE A  (class का default private)

वही rule, inheritance पर लागू: struct default में publicly inherit करता है, class privately. Practice में सब public explicitly लिखते हैं, तो यह कम ही परेशान करता है — लेकिन answer इससे पूरा होता है.

C struct vs C++ struct (confusion यहीं से आती है)

Feature	C struct	C++ struct
Member functions	❌ नहीं	✅ हां
Constructors/destructors	❌ नहीं	✅ हां
Access specifiers	❌ नहीं (सब public)	✅ private/protected/public
Inheritance	❌ नहीं	✅ हां
Variable declare करना	`struct Point p;`	`Point p;` (struct शब्द optional)

C++ programmers struct असल में कब use करते हैं?

struct — बिना किसी rule वाले plain data bundles के लिए: Point{x, y}, RGB colour, values का pair. "सब खुला है, आओ use करो."
class — जब data के rules हों और उसे functions के पीछे protect करना हो: BankAccount, validation वाला Student. "Data locked है, official दरवाज़ों से आओ."
Interview line: "Technically सिर्फ default access अलग है; convention से passive data के लिए struct, behaviour और rules वाले objects के लिए class."

Frequently Asked Questions

What is the only real difference between struct and class in C++?

Default access: struct members and inheritance are public by default, class members and inheritance are private by default. Both support functions, constructors and inheritance equally.

Can a struct have constructors and member functions in C++?

Yes. A C++ struct supports constructors, destructors, member functions, access specifiers and inheritance — only the C struct lacks these.

When should I use struct instead of class?

Use struct for simple passive data bundles where everything can be open (like a Point or RGB value); use class when data has rules and needs protection behind member functions.