Negation Error

Herkum has asked for the wisdom of the Perl Monks concerning the following question:

I keep getting this error only on my scripts running on Apache

Use of uninitialized value in negation (-) at /usr/local/perl5.10/lib/
+site_perl/5.10.0/i686-linux/DateTime.pm line 1651.
[download]

I have seen mentions of this type of error but no answer on what it is specifically supposed to cause this. Is this an XS error or something else?

Update: I did find the answer to my problem. While you can sort of get away with using cmp to compare dates, it will return an error because it is expecting a package name to be passed. What I should have been using was DateTime->compare( $dt1, $dt2 ) to compare the dates. The silences the error as well as sorts by date.

Comment on Negation Error Select or Download Code

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Re: Negation Error by broomduster (Priest) on Sep 21, 2008 at 00:19 UTC
I have version 0.4304 of DateTime (the latest). In that version, line 1651 is the `return` from `_compare_overload`: `sub _compare_overload { # note: $_[1]->compare( $_[0] ) is an error when $_[1] is not a # DateTime (such as the INFINITY value) return $_[2] ? - $_[0]->compare( $_[1] ) : $_[0]->compare( $_[1] ) +; }` [download] `_compare_overload` is overloaded to `<=>` and `cmp` for DateTime objects. So a good place to start tracking this down would be any place you compare DateTime objects (recognizing that the offending call/comparison may be coming from some other module that you are using).	[reply] [d/l] [select]
Re^2: Negation Error by Herkum (Parson) on Sep 21, 2008 at 01:13 UTC
OK, that is bizarre, considering I don't see it anywhere else in my application, but at least you pointed something to look at. The issue is that I take Date/Time from a database and cast all the rows as DateTime objects. So when I see a generic error like this, it makes me nervous as hell because I have no idea where to start because I am not doing anything special on the web server. Poking around for DT comparisons, that I can do. I certainly hope it is not in something that I did not write. :)	[reply]
Re^3: Negation Error by ikegami (Patriarch) on Sep 21, 2008 at 01:35 UTC
Do you sort DateTime objects? The default sorter is `$a cmp $b`.	[reply] [d/l]
Re^4: Negation Error by Herkum (Parson) on Sep 21, 2008 at 16:50 UTC
Re: Negation Error by GrandFather (Saint) on Sep 20, 2008 at 22:40 UTC
"Use of uninitialized value" is generated by Perl when you attempt to use the contents of a variable who's value hasn't been set. The actual error may be in either your code (you supply an uninitialised value for a parameter for example) or it may be an error in the module. Perl reduces RSI - it saves typing	[reply]