Custom Exception Messages

Custom exception messages can enhance error handling by providing detailed and context-specific information when exceptions are thrown. This is achieved by creating custom exception classes that inherit from the standard std::exception class and override its what() method to return informative error messages.

Creating Custom Exception Classes

A custom exception class allows you to define specific types of errors in your application with custom messages and additional context. This helps differentiate between different error scenarios and provide detailed information about what went wrong.

Steps to Create a Custom Exception Class:

1. Inherit from std::exception: Your custom exception class should derive from std::exception or a subclass like std::runtime_error. This ensures your custom exception is compatible with C++’s exception-handling mechanism.
2. Override the what() method: The what() method is inherited from std::exception and returns a C-style string (const char*). In your custom class, you can override it to return the error message.

Example: Custom Exception Class

#include <iostream>
#include <exception>
#include <string>

// Custom exception class inheriting from std::exception
class MyCustomException : public std::exception {
private:
    std::string message;

public:
    // Constructor to set the error message
    MyCustomException(const std::string& msg) : message(msg) {}

    // Override the what() method to return the custom error message
    virtual const char* what() const noexcept {
        return message.c_str();
    }
};

int main() {
    try {
        // Throwing a custom exception with a detailed message
        throw MyCustomException("An error occurred: invalid input provided.");
    } catch (const MyCustomException& e) {
        // Catching and printing the custom exception's message
        std::cerr << "Caught custom exception: " << e.what() << std::endl;
    }

    return 0;
}

Key Concepts

• Custom Message: The custom exception class holds an error message, which is passed through the constructor and stored in a member variable. The what() method returns this message.
• Detailed Error Reporting: The message can include relevant details like variable values, function names, or suggestions for debugging, giving more insight into the error.
• Exception Types: You can create multiple custom exception classes for different error types (e.g., FileNotFoundException, InvalidUserInputException), each with its own message.

Advantages of Custom Exception Messages:

1. Clarity and Readability: Provides clearer information about what caused the exception.
2. Easier Debugging: Detailed error messages can give developers context on what went wrong, reducing debugging time.
3. Separation of Concerns: Custom exceptions help differentiate different failure types within the program.

Example: Multiple Custom Exception Classes

class FileNotFoundException : public std::exception {
public:
    const char* what() const noexcept override {
        return "File not found error.";
    }
};

class InvalidUserInputException : public std::exception {
public:
    const char* what() const noexcept override {
        return "Invalid user input error.";
    }
};

int main() {
    try {
        throw FileNotFoundException();
    } catch (const std::exception& e) {
        std::cerr << "Caught: " << e.what() << std::endl;
    }

    try {
        throw InvalidUserInputException();
    } catch (const std::exception& e) {
        std::cerr << "Caught: " << e.what() << std::endl;
    }
}

Summary

• Custom exception messages in C++ allow developers to provide meaningful error descriptions by inheriting from std::exception.
• The custom what() method returns these messages, improving the clarity and usefulness of exceptions in error handling.
• This practice leads to better code maintainability, easier debugging, and a more robust error-management system.