Struct vs Class in C++: Key Differences and Usage

In C++, struct and class are very similar, but struct members are public by default while class members are private by default. Both can have functions, constructors, and inheritance, but their default access levels and typical usage differ.

Quick Comparison

Here is a quick side-by-side comparison of struct and class in C++.

Feature	struct	class
Default member access	public	private
Default inheritance access	public	private
Typical usage	Plain data structures, simple grouping	Complex data with encapsulation and behavior
Supports member functions	Yes	Yes
Supports constructors/destructors	Yes	Yes
Supports inheritance	Yes	Yes

Key Differences

The main difference between struct and class in C++ lies in their default access levels. In a struct, all members (variables and functions) are public by default, meaning they can be accessed from outside the struct without restrictions. In contrast, a class has all members private by default, so they cannot be accessed directly from outside unless explicitly declared public.

Another difference is the default inheritance mode. When you inherit from a struct, the inheritance is public by default, but when inheriting from a class, it is private by default. This affects how derived classes can access base class members.

Despite these differences, both struct and class can have member functions, constructors, destructors, and support inheritance. The choice between them is often about style and intent: struct is usually used for simple data holders, while class is preferred for encapsulating data with behavior and enforcing access control.

Code Comparison

Here is an example showing a struct with public members by default.

cpp

#include <iostream>

struct Point {
    int x;
    int y;

    void move(int dx, int dy) {
        x += dx;
        y += dy;
    }
};

int main() {
    Point p{1, 2};
    std::cout << "Before move: (" << p.x << ", " << p.y << ")\n";
    p.move(3, 4);
    std::cout << "After move: (" << p.x << ", " << p.y << ")\n";
    return 0;
}

Output

Before move: (1, 2)
After move: (4, 6)

Class Equivalent

The same example using a class requires explicit public access to allow outside access.

cpp

#include <iostream>

class Point {
public:
    int x;
    int y;

    void move(int dx, int dy) {
        x += dx;
        y += dy;
    }
};

int main() {
    Point p{1, 2};
    std::cout << "Before move: (" << p.x << ", " << p.y << ")\n";
    p.move(3, 4);
    std::cout << "After move: (" << p.x << ", " << p.y << ")\n";
    return 0;
}

Output

Before move: (1, 2)
After move: (4, 6)

When to Use Which

Choose struct when you want a simple data container with public access by default, like grouping related variables without complex behavior. It is ideal for plain data structures or POD (Plain Old Data) types.

Choose class when you want to encapsulate data and control access strictly, hiding implementation details and exposing only what is necessary. Use class for objects with behavior, invariants, and when you want to enforce encapsulation and abstraction.

Key Takeaways

Struct members are public by default; class members are private by default.

Both struct and class support functions, constructors, and inheritance.

Use struct for simple data grouping and class for encapsulated objects.

Default inheritance is public for struct, private for class.

Choosing between them depends on your design intent and access control needs.