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What is the difference between throw and throw ex inside a catch? What is the purpose of the finally block? How does a try/catch block work in C#, and what happens if no matching catch clause exists? When should you use using or await using? What are exception filters (when) and why use them? How do custom exception classes work in C#, and what's the recommended convention for creating one? What is exception filtering using the 'when' clause, and what advantage does it offer over catching and manually re-throwing? Why does 'throw;' (bare throw) preserve the original stack trace, while 'throw ex;' does not? When should you create custom exceptions vs use built-in ones? What is the recommended strategy for exceptions in a layered/enterprise app?
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C# › Exception Handling

What does the finally block guarantee, and when is it commonly used?

Beginner

Answer

Code in a finally block ALWAYS runs after the try (and any catch) block completes, whether an exception was thrown or not, and even if the try block contains a 'return' statement — making it the standard place for cleanup code like closing files or releasing resources.
FileStream? file = null;
try {
  file = File.OpenRead("data.txt");
  ProcessFile(file);
} finally {
  file?.Dispose(); // always runs, ensuring the file handle is released
}
Real-world example Guaranteeing a database connection or file handle is properly closed regardless of whether the operation succeeded or threw.

Common follow-ups: How does the 'using' statement relate to and often replace a manual try/finally for disposal?

File I/O & Streams
All 16 Exception Handling questions