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What is the difference between throw and throw ex?

Anubhav Sharma 616 19 Jun 2025

What is the difference between throw and throw ex?

c# c#
Updated 23 Jun 2025
Anubhav Sharma
Anubhav Sharma

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1 Answers

Ponu Maurya
Ponu Maurya 23 Jun 2025
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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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