Re: Answer: How do I find the index of the last element in an array?

An observation:

Juerd was just arguing against this syntax here today. I don't know what he means by: "$#foo + 1 isn't necessarily equal to @foo"(Some Perl array nuance I am not familiar with) but I tend to agree with him that using the more direct syntax:

print "index of last element: $#A";
[download]

is easier to understand and you don't have to leave future maintainers of your code guessing.

Thanks

Comment on Re: Answer: How do I find the index of the last element in an array? Download Code

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Re: Re: Answer: How do I find the index of the last element in an array? by Juerd (Abbot) on Jun 02, 2003 at 06:39 UTC
I don't know what he means by: "$#foo + 1 isn't necessarily equal to @foo"(Some Perl array nuance I am not familiar with) `$[ = 5; my @foo = qw(a b c); printf "Number of elements: %d\n", scalar @foo; printf "Last index: %d\n", $#foo; printf "Number of elements: %d\n", $#foo + 1; printf "Last index: %d\n", scalar @foo - 1;` [download] `Number of elements: 3 Last index: 7 Number of elements: 8 Last index: 2` [download] One should of course NEVER set `$[`, but that is besides the point. Juerd # { site => 'juerd.nl', plp_site => 'plp.juerd.nl', do_not_use => 'spamtrap' }	[reply] [d/l] [select]
Re: Re: Re: Answer: How do I find the index of the last element in an array? by pzbagel (Chaplain) on Jun 02, 2003 at 15:59 UTC
Of course! Thanks for that answer Juerd! I'm willing to bet that "One should of course NEVER set $[" is exactly what the Camel book said too when I read about it so long ago. Thanks for the refresher.	[reply]
Re: Re: Answer: How do I find the index of the last element in an array? by tommyw (Hermit) on Jun 02, 2003 at 14:23 UTC
If foo is an empty, or undefined, array, then `@foo` is undef, but `$#foo` is -1. In such a case, `$#foo` does equal `scalar(@foo)-1`, but `scalar(@foo)` does not equal `$#foo+1`. -- Tommy Too stupid to live. Too stubborn to die.	[reply] [d/l] [select]
Re: Re: Re: Answer: How do I find the index of the last element in an array? by edan (Curate) on Jun 02, 2003 at 14:41 UTC
No, I don't think so. If `@foo` is empty, then `scalar(@foo)` is zero, not undef, and the equality holds true... (actually `undef == 0` is also true, though it emits a warning) The only time `@foo != $#foo + 1` is when you messed with `$[` (but you didn't do that, did you?) -- 3dan	[reply] [d/l] [select]
Re: Re: Re: Re: Answer: How do I find the index of the last element in an array? by tommyw (Hermit) on Jun 02, 2003 at 14:50 UTC
Ack. Damn those non-scalar contexts! `perl -e 'print $#a, "\n", @a, "\n", $#a+1, "\n"' -1 0` [download] Thus clearly showing that @a is undef. Which is true. In a list context... If I'd remembered to include scalar around it: `perl -e 'print $#a, "\n", scalar (@a), "\n", $#a+1, "\n"' -1 0 0` [download] , I'd have got the right answer... My bad. -- Tommy Too stupid to live. Too stubborn to die.	[reply] [d/l] [select]