in reply to substr oddity
in thread Perl oddities

This doesn't seem to happen on Win32 5.8.4 (AS 810). Which version are you using? 

P:\test>perl -wle"sub foo{}; my $s =''; foo( substr $s, 2, 1 );"
substr outside of string at -e line 1.

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Examine what is said, not who speaks.
Silence betokens consent.
Love the truth but pardon error.

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Re^2: substr oddity
by Anonymous Monk on Mar 04, 2005 at 18:14 UTC
    This doesn't seem to happen on Win32 5.8.4 (AS 810). Which version are you using?

    Well, I'm running version "5.8.6 built for PA-RISC2.0-thread-multi-LP64", running on HP/UX. I also get the same behaviour for 5.6.1.

    But your snippet doesn't actually demonstrate the problem: you get the warning message, but can't actually detect whether the code crashed. Here's what I get when I add a trace statement after the call to substr(). 

    $ perl -wle 'sub foo{}; my $s=""; foo( substr($s,2,1) );print "Not rea
+ched\n"'
substr outside of string at -e line 1.
$

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    Note that "not reached" is never reached, and is not printed, because the code crashes on the substr() call.
    --
    Ytrew
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[d/l]

      Fair enough, but your snippet also doesn't crash on my machine for exactly the same reasons: 

      >perl # 5.8.4
use strict;
use warnings;
my $x="";
foo( substr($x,2,1) ); # crashes here
print "Alive!\n"; # not reached
sub foo {}
^Z
substr outside of string at - line 4.

>c:\perl561\bin\perl5.6.1.exe
use strict;
use warnings;
my $x="";
foo( substr($x,2,1) ); # crashes here
print "Alive!\n"; # not reached
sub foo {}
^Z
substr outside of string at - line 4.

      [download]
      Examine what is said, not who speaks.
      Silence betokens consent.
      Love the truth but pardon error.
[reply]
[d/l]
        Okay, I'm confused... is that your entire output? Was the word "Alive" in there somewhere?

        It should print "Alive!" if the code doesn't crash. I don't see that in your output. If that's your entire output, then you get what I do: a crash on the substr() call. Similarly, you'll get the same kind of crash if you assign to substr(): that is, treat it like an Lvalue.

        My guess is that because @_ can be assigned to, substr() behaves like an Lvalue when passed as a subroutine argument. If that's true, it's odd enough to be an oddity. :-)
        --
        Ytrew

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