What is the difference between simply using throw and throw ex, and which method is preferable in different cases?

Using throw and throw ex in a catch block in C# has important differences related to preserving the call stack of the exception.

• throw; — rethrows the current exception without modifying the call stack. This allows preserving the original point of error, which is important for debugging.

• throw ex; — rethrows the exception, but the call stack is reset and starts from the point of rethrow. This results in losing information about the original error location.

When to use what:

• If you just want to propagate the exception further, it's better to use throw;.
• If you need to modify or wrap the exception, you can use throw ex;, but it is usually preferable to create a new exception with an inner (InnerException) to preserve information.

Example:

try
{
    // code that may throw an exception
}
catch(Exception ex)
{
    // log or handle
    throw; // preserves the call stack
}