C++ Exceptions

advanced

Part of Advanced C++

Theory

Exceptions provide a way to handle runtime errors gracefully, separating error handling from normal program logic.

try / catch / throw

try {
    int age;
    std::cin >> age;
    if (age < 0) {
        throw std::invalid_argument("Age cannot be negative");
    }
} catch (const std::invalid_argument& e) {
    std::cerr << "Error: " << e.what() << std::endl;
} catch (const std::exception& e) {
    std::cerr << "General error: " << e.what() << std::endl;
}

Catch blocks are checked in order. Always catch derived classes before base classes.

Standard Exception Hierarchy

All standard exceptions derive from std::exception:

std::runtime_error — errors detectable at runtime
std::logic_error — errors detectable before runtime
std::invalid_argument — invalid argument values
std::out_of_range — index out of bounds
std::bad_alloc — memory allocation failure

Custom Exceptions

Create custom exception classes by inheriting from std::exception:

class InsufficientFunds : public std::exception {
public:
    const char* what() const noexcept override {
        return "Insufficient funds for withdrawal";
    }
};

RAII and Exceptions

RAII (Resource Acquisition Is Initialization) ties resource lifetime to object lifetime. When an exception causes stack unwinding, RAII objects are automatically destroyed, preventing resource leaks:

RAII with Exceptions

cpp

The noexcept Specifier

noexcept declares that a function does not throw exceptions:

int add(int a, int b) noexcept {
    return a + b;
}

The compiler can optimize noexcept functions better. Destructors and move operations should typically be noexcept.

Practical Examples

Example: Custom Exception and Error Handling

cpp

Exercises

Bank Account with Exception Handling

easy

Create a BankAccount class where withdraw() throws custom exceptions for insufficient funds and negative amounts. Use RAII for a transaction log.

Expected Output:

Deposited $500. Withdrew $200. Attempted overdraft: Insufficient funds.