C# – Difference between ‘throw’ and ‘throw new Exception()’

What is the difference between

try { ... }
catch{ throw }

and

try{ ... }
catch(Exception e) {throw new Exception(e.message) }

regardless that the second shows a message.

Best Answer

throw; rethrows the original exception and preserves its original stack trace.

throw ex; throws the original exception but resets the stack trace, destroying all stack trace information until your catch block.

NEVER write `throw ex;`

throw new Exception(ex.Message); is even worse. It creates a brand new Exception instance, losing the original stack trace of the exception, as well as its type. (eg, IOException).
In addition, some exceptions hold additional information (eg, ArgumentException.ParamName).
throw new Exception(ex.Message); will destroy this information too.

In certain cases, you may want to wrap all exceptions in a custom exception object, so that you can provide additional information about what the code was doing when the exception was thrown.

To do this, define a new class that inherits Exception, add all four exception constructors, and optionally an additional constructor that takes an InnerException as well as additional information, and throw your new exception class, passing ex as the InnerException parameter. By passing the original InnerException, you preserve all of the original exception's properties, including the stack trace.

This is the style that Microsoft tends to use in their examples.

It appears that the guidance in this area may have changed, as StyleCop now enforces the use of the C# specific aliases.

C# – Calling the base constructor in C#

Modify your constructor to the following so that it calls the base class constructor properly:

public class MyExceptionClass : Exception
{
    public MyExceptionClass(string message, string extrainfo) : base(message)
    {
        //other stuff here
    }
}

Note that a constructor is not something that you can call anytime within a method. That's the reason you're getting errors in your call in the constructor body.

Best Answer

NEVER write throw ex;

Related Solutions

C# – the difference between String and string in C#

This is the style that Microsoft tends to use in their examples.

C# – Calling the base constructor in C#

Related Topic

NEVER write `throw ex;`