C++ Exception Handling

What is Exception Handling?

Exceptions are runtime errors. C++ uses try, catch, and throw to handle them gracefully instead of crashing.

#include <iostream>
#include <stdexcept>
using namespace std;

double divide(double a, double b) {
    if (b == 0) throw invalid_argument("Division by zero!");
    return a / b;
}

int main() {
    try {
        cout << divide(10, 2)  << endl;   // 5
        cout << divide(10, 0)  << endl;   // throws!
    } catch (const invalid_argument& e) {
        cout << "Error: " << e.what() << endl;
    }
    cout << "Program continues..." << endl;
    return 0;
}

Output:

5
Error: Division by zero!
Program continues...

Multiple catch Blocks

try {
    int x = -1;
    if (x < 0)  throw out_of_range("Negative value");
    if (x == 0) throw runtime_error("Zero value");
}
catch (const out_of_range& e) {
    cout << "Range error: " << e.what() << endl;
}
catch (const runtime_error& e) {
    cout << "Runtime error: " << e.what() << endl;
}
catch (...) {
    cout << "Unknown error" << endl;
}

Custom Exceptions

class InsufficientFundsException : public exception {
  public:
    const char* what() const noexcept override {
        return "Insufficient funds in account";
    }
};

void withdraw(double balance, double amount) {
    if (amount > balance) throw InsufficientFundsException();
}

try {
    withdraw(100.0, 200.0);
} catch (const InsufficientFundsException& e) {
    cout << e.what() << endl;
}

#include <iostream>
#include <stdexcept>
using namespace std;

int getElement(int arr[], int size, int index) {
    if (index < 0 || index >= size)
        throw out_of_range("Index out of bounds: " + to_string(index));
    return arr[index];
}

int main() {
    int arr[] = {10, 20, 30, 40, 50};
    try {
        cout << getElement(arr, 5, 2)  << endl;   // 30
        cout << getElement(arr, 5, 10) << endl;   // throws
    } catch (const out_of_range& e) {
        cout << "Error: " << e.what() << endl;
    }
    return 0;
}

Summary

• throw raises an exception; try wraps risky code; catch handles it.
• Catch by const reference for efficiency.
• Use catch (...) as a fallback for unknown exceptions.
• Create custom exceptions by inheriting from std::exception.