What is the difference between “throw ex” and “throw”? Which one to use in real applications? with code

Throw ex will change the stack trace, where as throw will preserve the whole stack trace. 

Its a best practice to use throw as it preserve the whole stack trace.
 

There is a difference between using throw ex and throw statements when throwing exceptions:

throw ex:

• When you use throw ex, it rethrows the exception while resetting the stack trace.
• This means that the stack trace of the exception will start from the point of rethrowing, rather than the original location where the exception was thrown.
• As a result, the original source of the exception can be obscured, making it more challenging to diagnose the exact location where the exception originated.

throw:

• When you use throw without specifying an exception instance (throw;), it rethrows the current exception without resetting the stack trace.
• This preserves the original stack trace, allowing you to accurately identify the location where the exception was initially thrown.
• By using throw alone, you maintain the integrity of the exception's stack trace throughout the exception propagation.

Here's an example that demonstrates the difference between throw ex and throw:

using System;

public class Program
{
    public static void Main()
    {
        try
        {
            ThrowException();
        }
        catch (Exception ex)
        {
            Console.WriteLine("Using throw ex:");
            Console.WriteLine(ex.StackTrace);  // Stack trace starts from the line where the exception was rethrown
        }

        try
        {
            ThrowException();
        }
        catch (Exception ex)
        {
            Console.WriteLine("Using throw:");
            Console.WriteLine(ex.StackTrace);  // Stack trace reflects the original location where the exception was thrown
        }
    }

    public static void ThrowException()
    {
        try
        {
            // Simulating an exception
            throw new InvalidOperationException("Something went wrong.");
        }
        catch (Exception ex)
        {
            // Rethrowing the exception using throw ex
            throw ex;
        }
    }
}

In the above example, the ThrowException method throws an exception, which is then caught in the Main method. The exception is rethrown using both throw ex and throw statements, and the stack traces are displayed.

In real applications, it is generally recommended to use throw without specifying an exception instance (throw;) to preserve the original stack trace. This helps in accurate debugging and troubleshooting by providing the actual location where the exception occurred. By using throw alone, you maintain the integrity of the exception's stack trace throughout the exception propagation.

However, there might be certain scenarios where using throw ex could be useful, such as when you want to handle or log the exception at a particular level in the call stack and then rethrow it with a modified message or additional information.

Note: It's important to handle exceptions appropriately in your code and choose the appropriate approach based on your specific requirements and error handling strategy.