How can I create my own exception?

A better question imo is not how but why you would want to do this? Why not define two LogError overloads, one that takes an Exception and another that takes a string.

private static void LogError(Exception ex) { // write ex to one log file // write ex.message to another log file } private static void LogError(string error) { //nothing to write to exception-specific log file // write error info to another log file } 

It's not really advisable to generate your own Exception instance just for logging like this.

Have you considered factoring the // write ex.message to another log file behavior into a separate function and calling that with your desired string?

 if(CheckForSomething()) { try { // do something } catch (UnauthorizedAccessException ex) { LogException(ex); } catch (Exception ex) // Never do this. Do you know how to handle an OutOfMemoryException? { LogException(ex); } } else { string error = "Some error"; LogMessage(error); } private static void LogException(Exception ex) { // write ex to one log file LogMessage(ex.Message); } private static void LogMessage(string message) { // write message to another log file } 

you can also make you own exception class like this:

public class LogException: Exception { public LogException() : base() { } public LogException(string message) : base(message) { } } 

Exception e = new Exception(error); LogException ee = new LogException (Exception e); throw ee; 

Put this in the else block

You can do something like previously mentioned

LogException(new Exception("some error")); 

But it might be better to create your own exception class:

class MyException : Exception { //... } 

then

LogException(new MyException()); 

Some good solutions so far. You don't want to create a custom exception just for logging someone else will have a WTF? moment reading your code.

The alternative is to just extract the message from exception for the log.... something like

if(CheckForSomething()) { try { // do something } catch (UnauthorizedAccessException ex) { LogMessage(ex.Message); } } else { LogMessage("Some Error!"); } private static void LogMessage(string message) { //write message to log } 

Creating an exception for the sole purpose of passing it into a format handled by a method is a hack. It breaks the implicit understanding among programmers as to what exceptions are and what they are used for.