C++ Exception Handling: try/catch/throw, std::exception & Stack Unwinding

Exception Handling provides a structured mechanism to detect, transmit, and resolve unexpected runtime errors (such as network loss, missing files, or out-of-memory errors) without abruptly crashing the application.

Figure 17: The Standard C++ Exception Class Hierarchy (std::exception)

Custom Exception Class Implementation

#include <iostream>
#include <stdexcept>
#include <string>

// Custom domain exception deriving from std::runtime_error
class InsufficientFundsException : public std::runtime_error {
public:
    explicit InsufficientFundsException(double deficit)
        : std::runtime_error("Withdrawal rejected: Shortfall of $" + std::to_string(deficit)) {}
};

class BankAccount {
private:
    double balance;
public:
    BankAccount(double b) : balance(b) {}

    void withdraw(double amount) {
        if (amount > balance) {
            throw InsufficientFundsException(amount - balance); // Throw custom exception
        }
        balance -= amount;
        std::cout << "Withdrawal successful. Remaining: $" << balance << "\n";
    }
};

int main() {
    BankAccount account(500.0);

    try {
        account.withdraw(200.0);
        account.withdraw(450.0); // Throws InsufficientFundsException!
    } catch (const InsufficientFundsException& e) {
        std::cerr << "[ACCOUNT ERROR]: " << e.what() << "\n";
    } catch (const std::exception& e) {
        std::cerr << "[STANDARD ERROR]: " << e.what() << "\n";
    }

    return 0;
}