Incorporating modern exception handling and error reporting mechanisms in migrated C++ code

11 Oct 2023

When migrating legacy C++ code to a modern codebase, it is essential to update the exception handling and error reporting mechanisms. Modern C++ provides more robust and expressive features for handling exceptions and reporting errors, which can significantly enhance the quality and maintainability of the codebase.

In this blog post, we will explore some best practices for incorporating modern exception handling and error reporting mechanisms into migrated C++ code.

1. Exception Handling

1.1. Strong exception safety guarantees

Modern C++ encourages the use of exceptions for error handling. When adapting legacy code, you should strive to provide strong exception safety guarantees. This means ensuring that if an exception is thrown during an operation, the program state remains valid and no resources are leaked.

To achieve strong exception safety guarantees, consider the following:

Use standard exception classes like std::runtime_error or create custom exception classes that convey meaningful information about the error.
Wrap critical operations with try-catch blocks to handle exceptions gracefully.
Roll back any partial changes made before the exception was thrown to ensure a consistent program state.

For example:

try {
    // Critical operation that may throw an exception
    // ...
} catch (const std::exception& ex) {
    // Handle the exception gracefully
    // Log or display the error message
    // Roll back any partial changes
}

1.2. Using RAII for resource management

Resource Acquisition Is Initialization (RAII) is a powerful idiom in C++ that helps manage resources such as file handles, network connections, or memory allocations. The RAII principle guarantees that resources are properly released when they are no longer needed, even in the presence of exceptions.

When migrating legacy code, consider using RAII wrappers or smart pointers (such as std::unique_ptr or std::shared_ptr) to manage resources. These modern constructs ensure that resources are automatically released when the objects holding them go out of scope, regardless of whether an exception occurs or not.

Here’s an example of using std::unique_ptr for resource management:

std::unique_ptr<File> file;
try {
    file = std::make_unique<File>("example.txt");
    // Perform operations on the file
} catch (const std::exception& ex) {
    // Handle the exception gracefully
    // Log or display the error message
}
// The file resource will be automatically released at the end of the scope

2. Error Reporting

2.1. Centralized error reporting

In migrated C++ code, it is beneficial to have a centralized error reporting mechanism. This allows for consistent error handling and makes it easier to track and debug issues.

Consider creating an ErrorManager class or module that tracks error information and provides methods for reporting and handling errors. This class can encapsulate logging, displaying meaningful error messages to users, and tracking error codes or categories.

class ErrorManager {
public:
    static ErrorManager& instance() {
        static ErrorManager instance;
        return instance;
    }

    void logError(const std::string& errorMessage) {
        // Log the error message
    }

    void displayError(const std::string& errorMessage) {
        // Display the error message to the user
    }

    // Other error handling methods
    // ...
};

Using the ErrorManager class, you can report errors consistently across the codebase:

try {
    // Critical operation that may throw an exception
    // ...
} catch (const std::exception& ex) {
    ErrorManager::instance().logError(ex.what());
    ErrorManager::instance().displayError("An error occurred. Please try again later.");
    // Handle the error
}

2.2. Error codes and error categories

To provide more detailed information about errors, consider defining error codes or error categories. This approach can help diagnose issues more effectively and allow for targeted handling of specific types of errors.

Create an ErrorCodes enumeration or a set of constant values that represent different error codes or categories:

enum class ErrorCodes {
    None,
    InvalidInput,
    FileNotFound,
    NetworkError,
    // Other error codes
};

When an error occurs, you can associate the appropriate error code with the exception or error message and handle it accordingly:

try {
    // Critical operation that may throw an exception
    // ...
} catch (const std::exception& ex) {
    ErrorManager::instance().logError(ex.what(), ErrorCodes::NetworkError);
    ErrorManager::instance().displayError("A network error occurred. Please check your network connection.");
    // Handle the network error
}

Conclusion

Migrating C++ code to a modern codebase provides an opportunity to improve exception handling and error reporting mechanisms. By incorporating modern exception handling techniques such as strong exception safety guarantees and using RAII for resource management, you can enhance the reliability and maintainability of the code. Additionally, a centralized error reporting mechanism with error codes and categories can provide more detailed information for debugging and handling errors effectively.

Adapting legacy code to modern practices may require significant changes, but the long-term benefits in terms of code quality and maintainability make it worth the effort.