From @Abigail

Created by @Abigail

man perlsub states:

Any arguments passed in show up in the array "@_". There-
fore, if you called a function with two arguments, those
would be stored in "$_[0]" and "$_[1]". The array "@_" is
a local array, but its elements are aliases for the actual
scalar parameters. In particular, if an element "$_[0]"
is updated, the corresponding argument is updated (or an
error occurs if it is not updatable). If an argument is
an array or hash element which did not exist when the
function was called, that element is created only when
(and if) it is modified or a reference to it is taken.

Now, consider this program:

#!/usr/bin/perl -w

use strict;

sub mysub;

$, = " ";
$\ = "\n";

# 0 1 2 3
my @arr = ("cent", "nickel", "dime", undef);
$arr [5] = "dollar"; # Auto-vivifies $arr [4] to be 'undef'.

print map {defined $_ ? $_ : "^^"} @arr;
mysub @arr;
print map {defined $_ ? $_ : "^^"} @arr;

sub mysub {
$_ [0] = 0.01;
$_ [1] = 0.05;
$_ [2] = 0.10;
$_ [3] = 0.25;
$_ [4] = 0.50;
$_ [5] = 1.00;
}
__END__

If we run this, we get:
cent nickel dime ^^ ^^ dollar
0.01 0.05 0.1 0.25 ^^ 1

That is, $arr [4] isn't 0.50 after the function mysub was called,
while the documentation specifies it should.

bleadperl gives the same behaviour.

Abigail

Perl Info


Flags:
    category=core
    severity=low

Site configuration information for perl v5.6.1:

Configured by abigail at Tue Jul 10 12:17:49 CEST 2001.

Summary of my perl5 (revision 5.0 version 6 subversion 1) configuration:
  Platform:
    osname=linux, osvers=2.4.5, archname=i686-linux-64int-ld
    uname='linux hermione 2.4.5 #6 fri jun 22 01:38:20 pdt 2001 i686 unknown '
    config_args='-d -Dprefix=/opt/perl -Doptimize=-g -Dusemorebits'
    hint=recommended, useposix=true, d_sigaction=define
    usethreads=undef use5005threads=undef useithreads=undef usemultiplicity=undef
    useperlio=undef d_sfio=undef uselargefiles=define usesocks=undef
    use64bitint=define use64bitall=undef uselongdouble=define
  Compiler:
    cc='cc', ccflags ='-DDEBUGGING -fno-strict-aliasing -I/usr/local/include -I/opt/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-g',
    cppflags='-DDEBUGGING -fno-strict-aliasing -I/usr/local/include -I/opt/local/include'
    ccversion='', gccversion='2.95.3 20010315 (release)', gccosandvers=''
    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=12345678
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
    ivtype='long long', ivsize=8, nvtype='long double', nvsize=12, Off_t='off_t', lseeksize=8
    alignbytes=4, usemymalloc=n, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -L/usr/local/lib -L/opt/local/lib'
    libpth=/usr/local/lib /opt/local/lib /lib /usr/lib
    libs=-lnsl -lndbm -lgdbm -ldl -lm -lc -lcrypt -lutil
    perllibs=-lnsl -ldl -lm -lc -lcrypt -lutil
    libc=/lib/libc-2.2.3.so, so=so, useshrplib=false, libperl=libperl.a
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-rdynamic'
    cccdlflags='-fpic', lddlflags='-shared -L/usr/local/lib -L/opt/local/lib'

Locally applied patches:
    


@INC for perl v5.6.1:
    /home/abigail/Perl
    /home/abigail/Sybase
    /opt/perl/lib/5.6.1/i686-linux-64int-ld
    /opt/perl/lib/5.6.1
    /opt/perl/lib/site_perl/5.6.1/i686-linux-64int-ld
    /opt/perl/lib/site_perl/5.6.1
    /opt/perl/lib/site_perl
    .


Environment for perl v5.6.1:
    HOME=/home/abigail
    LANG (unset)
    LANGUAGE (unset)
    LC_ALL=POSIX
    LD_LIBRARY_PATH=/home/abigail/Lib:/usr/local/lib:/usr/lib:/lib:/usr/X11R6/lib:/opt/gnome/lib
    LOGDIR (unset)
    PATH=/home/abigail/Bin:/opt/perl/bin:/usr/local/bin:/usr/local/X11/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin:/sbin:/usr/X11R6/bin:/usr/games:/opt/povray/bin:/opt/gnome/bin:/opt/opera/bin:/usr/share/texmf/bin:/opt/Acrobat4/bin:/opt/java/blackdown/j2sdk1.3.1/bin:/usr/local/games/bin:/opt/gnuplot/bin:/opt/mysql/bin
    PERL5LIB=/home/abigail/Perl:/home/abigail/Sybase
    PERLDIR=/opt/perl
    PERL_BADLANG (unset)
    SHELL=/usr/bin/bash

Subroutine doesn't create elements. #5310

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