Exception handling is a powerful feature of C++ that allows developers to handle unexpected errors and exceptions in their code. In this blog, we will discuss what exceptions are, how to define and use them, and some best practices for using exception handling in C++.

What are exceptions?

An exception is an unexpected error or condition that occurs during the execution of a program. Examples of exceptions include division by zero, invalid input, or memory allocation failure.

In C++, exceptions are implemented as objects of a special class type. When an exception is thrown, the program looks for a catch block that can handle the exception. If no catch block is found, the program terminates with an error message.

Defining exceptions

To define a new exception in C++, we need to create a class that inherits from the standard exception class. Here is an example:

arduinoCopy code#include <exception>
#include <string>

class MyException : public std::exception {
public:
    MyException(const std::string& message) : message_(message) {}
    const char* what() const noexcept override {
        return message_.c_str();
    }
private:
    std::string message_;
};

In this example, we define a new exception class MyException that takes a message string as a constructor argument. We override the what() method to return the message string when the exception is caught.

Throwing exceptions

To throw an exception in C++, we use the throw keyword followed by the exception object. Here is an example:

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

In this example, we define a function divide() that takes two integers as arguments. If the second argument is zero, we throw a MyException with the message "Division by zero".

Catching exceptions

To catch an exception in C++, we use a try-catch block. Here is an example:

cCopy codetry {
    int result = divide(10, 0);
    std::cout << "Result: " << result << std::endl;
} catch (const MyException& e) {
    std::cerr << "Error: " << e.what() << std::endl;
}

In this example, we call the divide() function with arguments 10 and 0, which throws a MyException. We catch the exception using a catch block that takes a reference to a MyException object, and print the error message to the standard error output.

Best practices for using exception handling

When using exception handling in C++, there are some best practices that can help to ensure that your code is robust and easy to maintain.

Firstly, it's important to only use exceptions for exceptional conditions. Exceptions are more expensive than normal control flow, so using them for regular error handling can negatively impact performance.

Secondly, it's a good idea to define a hierarchy of exception classes that can handle different types of errors. This can make it easier to catch and handle different types of exceptions in different contexts.

Finally, it's important to always catch exceptions by reference rather than by value. Catching by value can lead to object slicing and other problems, whereas catching by reference ensures that the original exception object is preserved.