Constructors and Destructors

A constructor initialises an object when it is created; a destructor cleans it up when it goes out of scope or is deleted. Together they manage an object's full lifecycle.

Constructors

A constructor shares the class's name and has no return type. It runs automatically whenever an object is created, and is the ideal place to guarantee an object always starts in a valid state.

class Account {
public:
    std::string owner;
    double balance;

    // Constructor
    Account(std::string ownerName, double startingBalance) {
        owner = ownerName;
        balance = startingBalance;
    }
};

int main() {
    Account acc("Lerato", 500.00); // constructor runs automatically
    std::cout << acc.owner << ": R" << acc.balance << std::endl;
    return 0;
}

Destructors

A destructor is prefixed with a tilde (~) and takes no parameters. It runs automatically when an object's lifetime ends, and is commonly used to release resources such as dynamically allocated memory or open files.

class Logger {
public:
    Logger() { std::cout << "Logger started" << std::endl; }
    ~Logger() { std::cout << "Logger shutting down" << std::endl; }
};

Common Mistakes

• Giving a constructor a return type — constructors must never declare one, not even void.
• Forgetting that a class can have multiple overloaded constructors that accept different parameter lists.
• Assuming the destructor must be called manually — it runs automatically when an object leaves scope.
• Not initialising all member variables in a constructor, leaving some with unpredictable starting values.