C# Exception Handling Best Practices

Effective exception handling is crucial for building robust and maintainable C# applications. Following best practices ensures that your code behaves predictably even when unexpected situations arise.

1. Catch Specific Exceptions

Avoid catching the generic Exception class unless absolutely necessary. Catching specific exceptions allows you to handle different error conditions appropriately and prevents masking underlying issues. For example, catch ArgumentNullException specifically instead of just Exception.

try
{
    // Some operation that might throw a specific exception
    SomeMethodThatMightThrowArgumentNullException(null);
}
catch (ArgumentNullException ex)
{
    // Handle argument null exception specifically
    Console.WriteLine($"An argument was null: {ex.Message}");
}
catch (InvalidOperationException ex)
{
    // Handle invalid operation exception
    Console.WriteLine($"Operation was invalid: {ex.Message}");
}
catch (Exception ex) // Use sparingly for general cleanup or logging
{
    // Log the unexpected exception
    LogException(ex);
    throw; // Re-throw the exception if it cannot be handled here
}
                

2. Don't Suppress Exceptions

If you catch an exception, you should either handle it in a meaningful way or re-throw it. Simply catching an exception and doing nothing (or just logging it without re-throwing) can hide critical errors and make debugging significantly harder.

try
{
    // Operation that might fail
}
catch (Exception ex)
{
    // Log the error, but don't just swallow it
    LogError(ex);
    // Decide if re-throwing is appropriate
    // throw; // Re-throws the original exception
    // throw new CustomApplicationException("Operation failed", ex); // Wraps the exception
}
                

3. Throw Exceptions Early, Catch Them Late

Throw exceptions as soon as an invalid state or condition is detected. This makes the source of the error clear. Conversely, catch exceptions at the highest appropriate level in the call stack where they can be handled meaningfully, often at the application's entry point or in UI layers.

4. Use Custom Exceptions for Application-Specific Errors

While built-in exceptions cover many scenarios, define custom exception classes for application-specific error conditions. This improves code readability and allows for more granular exception handling.

public class InvalidOrderStateException : Exception
{
    public InvalidOrderStateException(string message) : base(message) {}
    public InvalidOrderStateException(string message, Exception innerException) : base(message, innerException) {}
}

// Usage:
if (!order.CanProcess())
{
    throw new InvalidOrderStateException("Order cannot be processed in its current state.");
}
                

5. Include Sufficient Information in Exceptions

When throwing an exception, provide a descriptive error message that explains what went wrong. If you catch and re-throw an exception, consider wrapping it with a new exception that provides more context about the current operation, while preserving the original exception as the InnerException.

try
{
    // File I/O operation
    ReadFromFile("data.txt");
}
catch (IOException ex)
{
    throw new ApplicationException($"Failed to read configuration file 'data.txt'.", ex);
}
                

6. Use `finally` for Resource Cleanup

The finally block is guaranteed to execute, regardless of whether an exception was thrown or caught. Use it to release unmanaged resources (like file handles, network connections, or database connections) and ensure your application doesn't leak resources.

StreamReader reader = null;
try
{
    reader = new StreamReader("log.txt");
    string line = reader.ReadLine();
    // ... process line ...
}
catch (IOException ex)
{
    // Handle specific IO errors
}
finally
{
    if (reader != null)
    {
        reader.Dispose(); // Or reader.Close()
    }
}
                

The using statement provides a more concise and often preferred way to achieve the same resource management:

try
{
    using (StreamReader reader = new StreamReader("log.txt"))
    {
        string line = reader.ReadLine();
        // ... process line ...
    } // reader.Dispose() is called automatically here
}
catch (IOException ex)
{
    // Handle specific IO errors
}
                

7. Avoid Using Exceptions for Control Flow

Exceptions are for exceptional circumstances, not for normal program logic. Using exceptions to control the flow of your application (e.g., to signal the end of a loop) makes code harder to understand, debug, and can be significantly less performant.

8. Document Your Exceptions

Clearly document the exceptions that your methods can throw, especially public APIs. This helps other developers understand how to use your code and how to handle potential errors.