How to pass array and hash data types to subroutines arguments in perl?

Question

I am facing compilation error while declaring array type argument in perl subroutine defination. My complete code is below:

use Data::Dumper;
use Win32;
use Win32::Service;
use strict;
use warnings;
my @Services = qw(NNMAction RpcEptMapper smstsmgr SNMPTRAP);
my $server   = 'nnmi.hclt.corp.hcl.in';
ServiceStatus($server , @Services);

sub ServiceStatus ($serverName,@serverServices)
{       my %statcodeHash = (     '1' => 'stopped',
                             '2' => 'start pending',
                             '3' => 'stop pending',
                             '4' => 'running',
                             '5' => 'continue pending',
                             '6' => 'pause pending',
                             '7' => 'paused'            );

  foreach my $serv (@serverServices)
  {     my %status;
     my $ret = Win32::Service::GetStatus($serverName , $serv , \%status);
     if ($ret)
     {       print "success \t$statcodeHash{$status{CurrentState}} \t$serv\n";
     }
     else
     {       print Win32::FormatMessage(Win32::GetLastError()), "\n";
     }
   }
 }

COMPILATION ERROR

>perl -w perl_RemoteServiceStatus.pl
Prototype after '@' for main::ServiceStatus : $serverName,@serverServices at per
l_RemoteServiceStatus.pl line 21.
Illegal character in prototype for main::ServiceStatus : $serverName,@serverServ
ices at perl_RemoteServiceStatus.pl line 21.
main::ServiceStatus() called too early to check prototype at perl_RemoteServiceS
tatus.pl line 16.
Global symbol "@serverServices" requires explicit package name at perl_RemoteSer
viceStatus.pl line 31.
Global symbol "$serverName" requires explicit package name at perl_RemoteService
Status.pl line 33.
Execution of perl_RemoteServiceStatus.pl aborted due to compilation errors.

Kindly help me debugging ths code. I am sure it would be a piece of cake for some.

perl has no mechanism for declaring argument types. prototypes look like they do that at first glance, but in fact serve a completely different purpose; you should not use them. — ysth
– ysth, Commented Dec 20, 2012 at 10:13

Chankey Pathak · Accepted Answer · 2012-12-20 10:12:26Z

10

It is really simple: Do not use prototypes if you do not know how they work. To get your code running, change the subroutine declaration from:

sub ServiceStatus ($serverName,@serverServices)
{ #...

to:

sub ServiceStatus {
    my ($serverName, @serverServices) = @_;

edit: If you need to pass more than one array/hash to a subroutine, or an array/hash should be passed-in before some other value(s), you have to pass it by reference:

sub complex_params {
    my ($array1, $scalar, $hash, $array2) = @_;

    # dereference
    my @a1 = @$array1;
    my @a2 = @$array2;
    my %h  = %$hash;

    #...
}

# reference
complex_params(\@some_array, $some_scalar, \%some_hash, \@other_array);

edited Dec 20, 2012 at 10:12

Chankey Pathak

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answered Dec 20, 2012 at 9:49

Matthias

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1 Comment

avimehenwal Over a year ago

Thanksyou Matthias ! It helped :) Will keep this thing in mind.

perreal · Accepted Answer · 2012-12-20 09:49:10Z

6

Perl prototypes are not for naming parameters, or even for giving types to them, they are for creating evaluation contexts. You need to modify the subroutines like this:

sub ServiceStatus ($@){
  my ($serverName,@serverServices) = @_;   
  # ...
}

or totally get rid of the prototype:

sub ServiceStatus {
  my ($serverName,@serverServices) = @_;   
  # ...
}

answered Dec 20, 2012 at 9:49

perreal

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1 Comment

avimehenwal Over a year ago

Excellent perreal. Got your message loud and clear :) Thanks

RobEarl · Accepted Answer · 2012-12-20 09:49:01Z

4

sub ServiceStatus
{
    my ($serverName,@serverServices) = @_; # Declare variables and populate from @_, the parameter list.
    ...

}

answered Dec 20, 2012 at 9:49

RobEarl

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2 Comments

avimehenwal Over a year ago

Thanks RobEarl for your valuable answer

Eric Hepperle - CodeSlayer2010 Over a year ago

This comment was helpful to me (in 2015) when having worked in PHP and JavaScript for over a year, and forgot about the @_ context with subs in Perl. Thanks

gaussblurinc · Accepted Answer · 2012-12-20 09:54:33Z

3

what are you doing?

First! Don't try to use prototypes:

sub ServiceStatus($@){

}

Let's see, what you want:

Passing array or hash to function is a very old trick:

sub ServiceStatus{
my ($firstArgument, $refToSecondArgumentWhichIsArray) = @_;

#return undef unless defined($firstArgument&&$refToSecondArgumentWhichIsArray);
...
}

How to use this?

ServiceStatus($serverName, \@serverServices);

And what to do with refs?

$refToArray->[0]; <- first element of array you pass
@{$refToArray}    <- array you pass to function

answered Dec 20, 2012 at 9:54

gaussblurinc

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1 Comment

avimehenwal Over a year ago

Thanks loldop for your valuable help. I got my mistake while declaring prototypes but unfortunately didnt got your clear message in last part.

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