What is the difference between throw and throw ex?

Question

Ponu Maurya · Answer

In C#, throw and throw ex both raise exceptions, but they behave differently when it comes to
preserving the original stack trace.
throw vs throw ex – Core Difference
Keyword
Stack Trace Preserved?
Use Case
throw
Yes
Rethrow original exception
throw ex
No
Replaces stack trace (avoid unless modifying)
1. throw – Rethrows the original exception
When you use throw alone inside a catch block, it 
rethrows the original exception without losing the stack trace.
try
{
    // Some code that throws
}
catch (Exception ex)
{
    // Do logging, then rethrow
    LogError(ex);
    throw; // ✅ Preserves original call stack
}
Keeps the exact line where the error occurred.Preferred for logging and rethrowing.
2. throw ex – Resets the stack trace
When you use throw ex, you create a new exception context, which
resets the stack trace to the current line. This makes debugging harder.
try
{
    // Some code that throws
}
catch (Exception ex)
{
    // ❌ Replaces original stack trace
    throw ex;
}
Looks like the error occurred in the catch block.You lose information about where the exception was originally thrown.
Example:
void Divide()
{
    try
    {
        int x = 0;
        int y = 10 / x; // Error: DivideByZeroException
    }
    catch (Exception ex)
    {
        throw;    // ✅ stack trace points here: int y = 10 / x
        // throw ex; // ❌ stack trace points here: throw ex
    }
}
Best Practice:
Always prefer throw when rethrowing an exception to preserve debugging details.
Use throw ex; only if:
You’re modifying the exception (e.g., wrapping it in another exception type).You’re deliberately restarting the stack trace for design reasons.
Wrapping Example (valid use of throw ex):
catch (Exception ex)
{
    throw new CustomAppException("Something failed.", ex);
}

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What is the difference between throw and throw ex?

Anubhav Kumar

Can you answer this question?

1 Answers

`throw` vs `throw ex` – Core Difference

1. `throw` – Rethrows the original exception

2. `throw ex` – Resets the stack trace

Example:

Best Practice:

Wrapping Example (valid use of `throw ex`):

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Keyword	Stack Trace Preserved?	Use Case
`throw`	Yes	Rethrow original exception
`throw ex`	No	Replaces stack trace (avoid unless modifying)