Re: trouble with each and a hash of hashes

perldoc -f each

When the hash is entirely read, a null array is returned in list context (which when assigned produces a false (0) value), ...

This leads me to believe that one of these could cause the problem:

You are exiting the "while ..(..each)" loop early, whthout exhausting the hash. The next time you return, it would pick up where it left off for that particular hash (If I understand the docs right).
You have another "each" working on the same hash elsewhere in the code, which exits early.

To "reset" the while (I would never do that in production code, before finding what causes the problem), simply do an throw-away keys() or (values) fetch prior to the "each".

Earth first! (We'll rob the other planets later)

Comment on Re: trouble with each and a hash of hashes

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Re: trouble with each and a hash of hashes by marcokuma (Novice) on Sep 11, 2004 at 22:26 UTC
Thanks a lot! Following the advice given to me by y'all and doing some more debugging I found out the problem: Once I find what I want during the "while ..(..each)" loop, I exit the loop. The next time, "each" starts from the pair in the list after the one where I stopped the previous time. If I exit the loop during the iteration in which "each" returned the very last pair in the list, the next time the loop is not even entered. So, I will go for a foreach loop instead. Well, thanks again -- now it looks obvious but I would have never been able to find out by myself! Marco	[reply]
Re^2: trouble with each and a hash of hashes by BrowserUk (Patriarch) on Sep 11, 2004 at 22:45 UTC
So, I will go for a foreach loop instead. As a solution, that will work fine--but it's not without it's downside. Using while each, avoids a (possibly significant) overhead that for keys or for values impose: that of constructing a list. If your hash is small, and if your going to iterate most of the elements anyway, then that may be acceptable. However, there is a better way: If you call keys on the hash(ref) before entering your while loop, it will reset the iterator and you will avoid the problems you detailed above. keys is specifically optimised for this purpose. From perlfunc: As a side effect, calling keys() resets the HASH's internal iterator, see each. (In particular, calling keys() in void context resets the iterator with no other overhead.) Examine what is said, not who speaks. "Efficiency is intelligent laziness." -David Dunham "Think for yourself!" - Abigail "Memory, processor, disk in that order on the hardware side. Algorithm, algorithm, algorithm on the code side." - tachyon	[reply]