3 ways to leave your exception

September 08, 2009

Below is a small reference showing, by example, the 3 ways of throwing/re-throwing exceptions in C#, and their outcomes.

	class Program
	{
	static void Main(string[] args)
	{
	// Output:
	//
	// Invalid operation: Could not find file 'C:\this doesnt exist.txt'.
	// Could not find file 'C:\this doesnt exist.txt'.
	// Could not find file 'C:\this doesnt exist.txt'.
	//
	try
	{
	ThrowTest.ThrowNew();
	}
	catch (Exception ex)
	{
	Console.WriteLine(ex.Message);
	}
	try
	{
	ThrowTest.Throw();
	}
	catch (Exception ex)
	{
	Console.WriteLine(ex.Message);
	}
	try
	{
	ThrowTest.ThrowEx();
	}
	catch (Exception ex)
	{
	Console.WriteLine(ex.Message);
	}
	Console.ReadLine();
	}
	}

	public class ThrowTest
	{
	public static void ThrowNew()
	{
	try
	{
	File.OpenText(@"C:\this doesnt exist.txt");
	}
	catch (IOException ex)
	{
	// InnerException is null, and the stacktrace starts at ThrowNew()
	throw new InvalidOperationException("Invalid operation: " + ex.Message);
	}
	}
	public static void Throw()
	{
	try
	{
	File.OpenText(@"C:\this doesnt exist.txt");
	}
	catch (IOException ex)
	{
	// This maintains the entire stacktrace, so will include the chain that occured inside the Framework,
	// i.e. at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
	throw;
	}
	}
	public static void ThrowEx()
	{
	try
	{
	File.OpenText(@"C:\this doesnt exist.txt");
	}
	catch (IOException ex)
	{
	// InnerException is null, and the stacktrace starts at ThrowEx(). It's the least useful of the three.
	throw ex;
	}
	}
	}

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I'm Chris Small, a software engineer working in London. This is my tech blog. Find out more about me via Github, Stackoverflow, Resume