When should you use a class vs a struct in C++?

When to Use a Class vs a Struct in C++

In C++, both classes and structs are user-defined types that allow you to group related data and functions together. While they are largely similar, there are key differences in their default access levels and intended usage. Understanding when to use a class versus a struct can help you write more organized and maintainable code.

What Are Classes and Structs?

Class: A class in C++ is a blueprint for creating objects. It can contain data members (variables) and member functions (methods) that operate on the data. Classes support features like inheritance, encapsulation, and polymorphism, which are fundamental to object-oriented programming (OOP).

class Car {
public:
    void drive() {
        // Driving logic
    }

private:
    int speed;
};

Struct: A struct, short for structure, is similar to a class but with some differences in default access levels. Originally, structs were used in C for grouping data, but C++ has extended their functionality to include member functions and other OOP features.

struct Point {
    double x;
    double y;

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

Key Differences Between Class and Struct

1. Default Access Specifier:

   • Class: Members are private by default.
   • Struct: Members are public by default.

   class MyClass {
       int x; // Private by default
   };
   
   struct MyStruct {
       int x; // Public by default
   };

2. Inheritance:

   • Class: Inherits privately by default.
   • Struct: Inherits publicly by default.

   class BaseClass {};
   class DerivedClass : BaseClass {}; // Private inheritance
   
   struct BaseStruct {};
   struct DerivedStruct : BaseStruct {}; // Public inheritance

3. Intended Use:

   • Class: Typically used for more complex data structures and encapsulating behavior.
   • Struct: Generally used for plain data structures without complex behavior.

When to Use a Class

1. Encapsulation and Data Hiding: Use classes when you want to encapsulate data and hide implementation details. This promotes better data protection and abstraction.

   class BankAccount {
   private:
       double balance;
   
   public:
       void deposit(double amount) {
           balance += amount;
       }
   
       double getBalance() const {
           return balance;
       }
   };

2. Object-Oriented Features: Classes are preferable when leveraging OOP features like inheritance, polymorphism, and encapsulation.

   class Shape {
   public:
       virtual void draw() = 0; // Pure virtual function
   };
   
   class Circle : public Shape {
   public:
       void draw() override {
           // Draw a circle
       }
   };

When to Use a Struct

1. Plain Data Structures: Use structs for simple data containers that primarily store data without significant behavior.

   struct Point {
       double x;
       double y;
   };

2. Interoperability with C: Structs are useful when interfacing with C code or APIs that expect C-style structures.

   extern "C" {
       struct CStruct {
           int id;
           char name[50];
       };
   }

3. Transparent Data Access: When you want all members to be publicly accessible without needing getter and setter functions.

   struct Config {
       std::string hostname;
       int port;
   };

Best Practices

1. Use Classes for Complex Types: When your type involves behavior, encapsulation, and interactions, prefer using classes.

2. Use Structs for Simple Aggregates: For types that are primarily data holders without needing encapsulation or behavior, structs are appropriate.

3. Follow Consistent Naming Conventions: Maintain consistency in your codebase by using classes and structs according to their intended uses.

4. Consider Future Extensions: Even if a data structure is simple now, if you anticipate adding behavior later, starting with a class might be more suitable.

Practical Examples

Class Example:

class Employee {
private:
    std::string name;
    double salary;

public:
    Employee(const std::string& name, double salary) : name(name), salary(salary) {}

    void promote(double increase) {
        salary += increase;
    }

    double getSalary() const {
        return salary;
    }
};

Struct Example:

struct Rectangle {
    double width;
    double height;

    double area() const {
        return width * height;
    }
};

Additional Resources

Enhance your understanding of object-oriented design and prepare for interviews with the Grokking the Object Oriented Design Interview course on DesignGurus.io.

Helpful Blogs

Dive deeper into software design principles by visiting DesignGurus.io's blog:

• Essential Software Design Principles You Should Know Before the Interview
• Mastering the FAANG Interview: The Ultimate Guide for Software Engineers

By understanding when to use classes versus structs, you can create more organized, maintainable, and efficient C++ code. Happy coding!