Perl: Passing by reference does not modify the hash -

-

my understanding in perl pass hashes functions reference

consider following example, modify hash in modifyhash function

#!/usr/local/bin/perl  %hash;  $hash{"a"} = "1"; $hash{"b"} = "2";   print (keys %hash); print "\n";  modifyhash(\%hash);  print (keys %hash); print "\n";  sub modifyhash {     $hashref = @_[0];     %myhash = %$hashref;     $myhash{"c"} = "3";     print (keys %myhash);     print "\n"; }

the output of script is:

ab abc ab

i have expected be:

ab abc abc

...as pass hash reference.

what concept missing here passing hashes functions?

that's because when my %myhash = %$hashref;, you're taking copy of dereferenced $hashref , putting %myhash same thing my %myhash = %hash;, you're not working on referenced hash @ all.

to work on hash specified reference, try this...

sub modifyhash {     $hashref = $_[0];     $hashref->{"c"} = "3";     print (keys %$hashref);     print "\n"; }

as pointed out thissuitisblacknot in comments below, @_[0] better written $_[0]. should using use strict; , use warnings;, have been caught. because you're sending in reference, have used my $hashref = shift;.


Comments

Post a Comment

Popular posts from this blog

yii2 - Yii 2 Running a Cron in the basic template -

-
i have seen instructions on running cron in advanced template, cant figure out how on basic template. have following controller in basic controllers folder. <?php namespace app\controllers; use yii\console\controller; /** * cron controller */ class croncontroller extends controller { public function actionindex() { echo "cron service runnning"; } public function actionmail($to) { echo "sending mail " . $to; } } i have navigated root of application , tried these comands yii cron php yii cron im getting unknown comand "cron" i know old question failed find actual answer this. if @ code yii exec file you'll notice requires /common/config/aliases.php file console/config/main.php. can naturally change these or copy on these advanced template. hope solves problem wanting same thing.
Read more

asp.net - 'System.Web.HttpContext' does not contain a definition for 'GetOwinContext' Mystery -

-
i realize question might seem trivial some, it's these types of things find myself fighting quite bit , want make sense of despite seeming losing battle in .net (for me anyway). so, if following: using system.web; ... applicationuser user = system.web.httpcontext.getowincontext().getusermanager<applicationusermanager>().findbyid(system.web.httpcontext.user.identity.getuserid()); that produces error in title , red getowincontext() , error cannot resolve symbol 'getowincontext()' however, if following (remove system.web in front of httpcontext ), works expected (or @ least no errors): using system.web; ... applicationuser user = httpcontext.getowincontext().getusermanager<applicationusermanager>().findbyid(system.web.httpcontext.user.identity.getuserid()); however, if (same line that's working using system.web commented out): //using system.web; ... applicationuser user = httpcontext.getowincontext().getusermana...
Read more

mercurial graft feature, can it copy? -

-
there new feature in mercurial 3, called 'graft' (graft local). job of moving change-set different branch. is there way "copy" change-set branch? i interested in in moving stuff qa branch production branch, still need code reside in qa. want copy. found , have tried few things, maybe it'll become clear more tinkering , reading... does have better way of 'cherry picking' change-sets move cross branch (or trunk)??? graft copies changesets, doesn't move them. hg graft (emphasis mine): this command uses mercurial's merge logic copy individual changes other branches without merging branches in history graph. known 'backporting' or 'cherry-picking' . default, graft copy user, date, , description source changesets.
Read more