How to catch and re-throw exceptions
There are two ways to catch and re-throw an exception, below the two code snippets:
Snippet #1:
1: try
2: {
3:
4: }
5: catch(Exception ex)
6: {
7: throw ex;
8: }
Snippet #2:
1: try
2: {
3:
4: }
5: catch(Exception ex)
6: {
7: throw;
8: }
When you use snippet #1, you will re-throw the same exception object and as result of this the original stack trace will be lost. Snippet #2 will maintain the original stack trace, this is very useful for debugging.
One of the try/catch general exception handling guidelines says:
“Do not rethrow by throwing the same exception object. This causes the stack trace for the original exception to be lost--use a lone "throw;" statement (without an object following it) to "rethrow" a catch exception.”
The best way to see the difference is with a code example:
1: class Program
2: {
3: static void Main(string[] args)
4: {
5: try
6: {
7: Method1();
8: }
9: catch (Exception ex)
10: {
11: throw;
12: }
13: }
14:
15: public static void Method1()
16: {
17: Method2();
18: }
19:
20: public static void Method2()
21: {
22: throw new Exception();
23: }
24: }
The following stack trace will be produced by the code example above:
at ConsoleApplication2.Program.Method2()
at ConsoleApplication2.Program.Method1()
at ConsoleApplication2.Program.Main(String[] args)
at System.AppDomain.ExecuteAssembly(Assembly assembly, String[] args)
at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart()
When you use throw ex; instead of throw; you will get:
at ConsoleApplication2.Program.Main(String[] args)
at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args)
at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart()
As you see the stack trace don’t have the calls to Method1 and Method2, so when you use throw ex; you will lose essential debug information.