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Re: Re: Re: Re: for loop localisation bug?

by Corion (Pope)
on Dec 29, 2003 at 23:18 UTC ( #317580=note: print w/replies, xml ) Need Help??

in reply to Re: Re: Re: for loop localisation bug?
in thread for loop localisation bug?

After some searching, I found this link for Pascal, which tells what I know about Pascal, that the value is undefined after leaving the loop. I think that Turbo Pascal and Borland Pascal had the value of the upper bound of the loop at the end of the loop, but confusion started once they implemented optimizations in BP7 and Delphi.

For C, I browsed the standard a bit, but didn't stumble on anything going in either direction, so I guess the behaviour is neither implementation defined nor undefined but merely unspecified (some FAQ goes to some lengths to explain the differences between these three regarding the ANSI C standard...). I guess that one will find ugly differences soon enough if one uses enough different compilers and not only gcc...

The same pages as for the Pascal link give some remarks about C loops, but also no hint as to what the value of the loop iterator is after leaving the loop.

perl -MHTTP::Daemon -MHTTP::Response -MLWP::Simple -e ' ; # The $d = new HTTP::Daemon and fork and getprint $d->url and exit;#spider ($c = $d->accept())->get_request(); $c->send_response( new #in the HTTP::Response(200,$_,$_,qq(Just another Perl hacker\n))); ' # web

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Re: Re: Re: Re: Re: for loop localisation bug?
by BrowserUk (Pope) on Dec 30, 2003 at 00:15 UTC

    I said my Pascal was a long time ago:) I dug up a little info on the last Pascal compiler I used -- in a museum!

    For C, I think the info I dug up and posted here is reasonably definitive. With deference to MADuran's info on C99 which I've never encountered, there is no definitive statement on the state of a C for loop variable after a for loop, simply because there is nothing special about a for loop variable in C.

    • It is simply a variable that has a scope defined by the block in which it is declared.
    • It must have been declared before it can be used in the for loop.
    • Any modifications made to it, either by the control statements or within the for loop body, persist after the for loop terminates, and until it goes out of scope.
    • It remains in scope, until the block it was defined in, ends.

    One all. Now lets get back to perl:)

    Examine what is said, not who speaks.
    "Efficiency is intelligent laziness." -David Dunham
    "Think for yourself!" - Abigail

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