It is not very difficult if you enable warnings; it says "Use of freed value in iteration". Note that $a{b} is deleted in both iterations, yet on on of the iterations it tries to derefence its value of the key (the value is already freed, along with the key.) The program decides to exit with die() and does not crash.

It shouldn't coredump at all, and it doesn't for me. If you have a perl older than 5.8.1 then I would suggest you upgrade. If you have a newer one then I would use perlbug to submit this as a bug report.

/J\

Who is giving you these snippets? Is someone putting you up to this?

You've been around awhile here, so I'm sure by now you've read perlfaq4. But just in case, here's an excerpt from it that seems relevant and fairly direct:

What happens if I add or remove keys from a hash while iterating over it?

(contributed by brian d foy)

The easy answer is "Don't do that!"

If you iterate through the hash with each(), you can delete the key most recently returned without worrying about it. If you delete or add other keys, the iterator may skip or double up on them since perl may rearrange the hash table. See the entry for each() in perlfunc.

Please tell us which version of Perl is segfaulting with the code snippet you provided. I am anxious to hear the answer.

Use of freed value in iteration at dump.pl line 8.
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