Error / Exception Handling in C#

Handle errors with try/catch/finally, catch filters (when), throw expressions, custom exceptions, AggregateException, and global exception handlers.

Introduction to Exceptions

1. What is an Exception?

An exception is a runtime error that disrupts the normal flow of execution.

Types of Exceptions

1. System Exceptions (Runtime Errors)

Built-in exceptions thrown by the .NET runtime for programming mistakes.

2. Application Exceptions (Domain Errors)

`ApplicationException` is the base for user-defined exceptions.

3. Common Exception Types

Quick reference of the most frequently encountered exceptions.

try / catch

1. Basic try-catch

Wrap risky code in `try` and handle the error in `catch`.

2. The Exception Object

The caught exception exposes `Message`, `StackTrace`, and `InnerException`.

3. Multi-catch

Use multiple `catch` blocks to handle different exception types differently.

finally Block

1. finally Execution

`finally` runs whether the try block succeeded or threw.

Throwing Exceptions

1. throw new Exception

Use `throw` to raise an exception from your own code.

2. Rethrow — throw vs throw ex

Use bare `throw` to rethrow without losing the original stack trace.

Custom Exception Classes

1. Extending Exception

Inherit from `Exception` to create meaningful domain exceptions.

Error Propagation

1. Exception Bubbling

An unhandled exception travels up through each caller until caught.

using / IDisposable

1. using Statement (Automatic Resource Closing)

`using` calls `Dispose()` automatically — even if an exception is thrown.

2. Custom IDisposable

Implement `IDisposable` to make your own class work with `using`.

Stack Trace & Call Stack

1. What is a Stack Trace?

A stack trace shows the chain of method calls at the moment an exception was thrown.

2. Getting Stack Trace Without an Exception

`Environment.StackTrace` gives the current call stack at any point.

Exception Filters

1. catch (Exception ex) when (...)

`when` adds a condition to a catch block — the exception is only caught if the condition is true.