Exception Handling in C++ – Writing Robust Programs

In real-world software, things can go wrong: a file might not open, a network might fail, or an invalid value might sneak into your program. Exception handling is a key feature in C++ that allows you to gracefully manage such errors without crashing the entire program.

In this guide, you’ll learn:

• What exception handling is
• How to use try, catch, and throw
• What types of exceptions exist
• Best practices for writing clean, maintainable error-handling code

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What is Exception Handling?

Exception handling in C++ is a mechanism to handle runtime errors — errors that occur while the program is running, not during compilation.

Rather than using return codes or flags, C++ lets you “throw” exceptions when something goes wrong, and “catch” them where you can respond appropriately.

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Basic Syntax

try {
    // Code that may throw an exception
} catch (exception_type variable) {
    // Code that handles the exception
}

Example:

#include <iostream>
using namespace std;

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

int main() {
    try {
        int result = divide(10, 0);
        cout << "Result: " << result << endl;
    } catch (const char* msg) {
        cout << "Error: " << msg << endl;
    }
    return 0;
}

Output:

Error: Division by zero!

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The throw Keyword

You use throw to signal that an exception has occurred.

throw value; // value can be an int, string, object, etc.

Examples:

throw -1;                     // throws an int
throw "Invalid input";        // throws a C-string
throw std::runtime_error("File not found"); // throws a standard exception object

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The try Block

Put all code that might throw an exception inside a try block.

try {
    risky_function();
}

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The catch Block

catch handles the error. You can have multiple catch blocks for different exception types.

catch (int e) {
    // Handle int exceptions
}
catch (const char* msg) {
    // Handle C-string exceptions
}
catch (...) {
    // Catch-all handler for any exception type
}

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Example with Multiple Catch Blocks

try {
    throw 3.14;
} catch (int e) {
    cout << "Caught int: " << e << endl;
} catch (double e) {
    cout << "Caught double: " << e << endl;
} catch (...) {
    cout << "Caught unknown exception." << endl;
}

Output:

Caught double: 3.14

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Standard Exceptions in C++

C++ provides a set of predefined exception classes in the <stdexcept> header.

Common ones:

• std::runtime_error
• std::invalid_argument
• std::out_of_range
• std::overflow_error
• std::underflow_error
• std::logic_error

Example:

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

int main() {
    try {
        throw std::out_of_range("Index out of range!");
    } catch (const std::exception& e) {
        cout << "Caught exception: " << e.what() << endl;
    }
    return 0;
}

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Custom Exception Classes

You can define your own exception class by inheriting from std::exception.

class MyException : public std::exception {
public:
    const char* what() const noexcept override {
        return "Custom exception occurred!";
    }
};

Use it like this:throw MyException();


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Nested Try-Catch Blocks

You can also use try-catch inside other try-catch blocks:

try {
    try {
        throw 100;
    } catch (int x) {
        cout << "Inner catch: " << x << endl;
        throw; // rethrow
    }
} catch (...) {
    cout << "Outer catch." << endl;
}

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Best Practices

1. Throw exceptions, don’t return error codes
2. Use standard exceptions where possible
3. Catch exceptions by reference, especially for objects
4. Avoid exception handling in performance-critical code, if not needed
5. Use RAII (Resource Acquisition Is Initialization) to avoid memory leaks on exceptions
6. Never throw exceptions from destructors

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Final Thoughts

Exception handling in C++ allows you to write safer, more robust applications by properly managing unexpected runtime errors. It’s essential in real-world development where external inputs, resources, and logic can often go wrong.

Understanding how to use try, catch, and throw — along with proper exception design — is a fundamental part of writing professional-grade C++ code.