Advanced Coding & Software Engineering Program

Exception Handling in C++

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Last Updated on: 22nd Dec 2025 15:05:32 PM

1. Introduction to Exception Handling in C++

In C++, Exception Handling is a powerful mechanism used to handle runtime errors in a program in a graceful and controlled manner.

 

Instead of terminating the program abruptly when an error occurs, exception handling allows the program to:

• Detect the error

• Transfer control to a special block

• Handle the error properly

• Continue or terminate safely

 

2. What is an Exception?

An exception is an unexpected runtime problem that disrupts the normal flow of program execution.

 

Examples of Exceptions:

• Division by zero

• Accessing invalid array index

• File not found

• Memory allocation failure

 

3. Real-Life Example of Exception Handling

Example: Traffic Signal System

• Green → normal flow

• Red → stop

• Accident occurs → traffic police intervenes

👉 Accident = Exception
👉 Traffic police = Exception handler

 

Without police, traffic would collapse.
Without exception handling, programs crash.

 

4. Why Exception Handling is Needed?

Without exception handling

• Program crashes suddenly

• Poor user experience

• Difficult debugging

 

With exception handling

• Smooth error handling

• Better program reliability

• Cleaner and maintainable code

 

5. Keywords Used in Exception Handling

C++ provides three main keywords:

Keyword	Purpose
try	Block where exception may occur
throw	Throws an exception
catch	Handles the exception

 

6. Basic Syntax of Exception Handling

try {
    // code that may cause exception
}
catch (exception_type) {
    // code to handle exception
}

 

7. Simple Example of Exception Handling

If division by zero occurs, the program throws an exception and handles it safely.

 

Example

#include <iostream>
using namespace std;

int main() {
    int a = 10, b = 0;

    try {
        if (b == 0)
            throw b;
        cout << "Result: " << a / b << endl;
    }
    catch (int x) {
        cout << "Error: Division by zero is not allowed" << endl;
    }

    return 0;
}

 

Output

Error: Division by zero is not allowed

 

Explanation of Output

• Division by zero detected

• Exception thrown using throw

• catch block handles the error

 

8. Multiple Catch Blocks

A program may face different types of exceptions, so multiple catch blocks are used.

 

Example 

#include <iostream>
using namespace std;

int main() {
    try {
        throw 3.14;
    }
    catch (int x) {
        cout << "Integer exception caught" << endl;
    }
    catch (double y) {
        cout << "Double exception caught" << endl;
    }

    return 0;
}

 

Output

Double exception caught

 

Explanation of Output

• Exception type is double

• Matching catch block executes

 

9. Catch-All Handler ( catch(...) )

Used when you don’t know the type of exception.

 

Example 

#include <iostream>
using namespace std;

int main() {
    try {
        throw 'A';
    }
    catch (...) {
        cout << "Unknown exception caught" << endl;
    }

    return 0;
}

 

Output

Unknown exception caught

 

Explanation of Output

• Handles all exception types

• Should be placed at the end

 

10. Exception Handling with Functions

Exceptions can be thrown inside functions and caught in  main(). 

 

Example 

#include <iostream>
using namespace std;

void checkAge(int age) {
    if (age < 18)
        throw age;
    else
        cout << "Eligible for voting" << endl;
}

int main() {
    try {
        checkAge(16);
    }
    catch (int a) {
        cout << "Not eligible. Age = " << a << endl;
    }

    return 0;
}

 

Output

Not eligible. Age = 16

 

Explanation of Output

• Function throws exception

• Main function handles it

 

11. Real-Life Use Case of Function Exception

Example: Online Exam System

• If student age < required → exception

• System shows proper error message

• Exam not started

 

12. Nested Try-Catch Blocks

Concept Explanation

 try  blocks can exist inside another try block.

 

Example 

#include <iostream>
using namespace std;

int main() {
    try {
        try {
            throw 10;
        }
        catch (int x) {
            cout << "Inner catch: " << x << endl;
            throw;
        }
    }
    catch (int y) {
        cout << "Outer catch: " << y << endl;
    }

    return 0;
}

 

Output

Inner catch: 10
Outer catch: 10

 

Explanation of Output

• Exception rethrown

• Handled by outer  catch 

 

13. Standard Exception Classes in C++

C++ provides built-in exception classes in  <exception>. 

Class	Description
exception	Base class
bad_alloc	Memory allocation failure
out_of_range	Index error
runtime_error	Runtime issue

 

14. Example Using  bad_alloc 

Complete Program

#include <iostream>
using namespace std;

int main() {
    try {
        int *p = new int[100000000000];
    }
    catch (bad_alloc &e) {
        cout << "Memory allocation failed" << endl;
    }

    return 0;
}

 

15. Advantages of Exception Handling

✔ Prevents program crash
✔ Improves reliability
✔ Separates error logic from normal logic
✔ Better debugging and maintenance

 

16. Disadvantages of Exception Handling

❌ Slight performance overhead
❌ Complex for beginners
❌ Misuse can make code unreadable

 

17. Common Mistakes

❌ Not catching thrown exception
❌ Catching wrong data type
❌ Using exceptions for normal logic

 

18. Interview Questions

1. What is exception handling?

2. Difference between error and exception?

3. What is try, throw, catch?

4. What is catch-all handler?

5. Can multiple catch blocks be used?

 

19. Real-World Applications

• Banking software

• Online payment systems

• File handling systems

• Game engines

• Operating systems

 

20. Conclusion

Exception Handling in C++ is an essential concept for writing robust, safe, and professional programs. It allows developers to handle runtime errors gracefully without

crashing the application. By using  try ,  throw , and  catch , programmers can separate error-handling code from normal logic, making programs easier to debug and maintain. In real-world applications like banking systems, online exams, and payment gateways, exception handling plays a crucial role in ensuring reliability and a smooth user experience. Mastering exception handling is a key step toward becoming a skilled C++ programmer.

 

Keep practicing — you're doing amazing!

Happy Coding!    

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