How to access an element in a Perl array from a reference to an array of references

Question

I have the following Perl code:

package CustomerCredit;
#!/usr/local/bin/perl
use 5.010;
use strict;

my $TransRef = @_; # This code comes from a sub within the package.
my ($Loop, $TransArrRef, $TransID);
for ($Loop = 0; $Loop < $$#TransRef; $Loop++)
{
   $TransArrRef = $$TransRef[$Loop]; # Gets a ref to an array.
   $TransID = $$TransArrRef[0];  # Try to get the first value in the array.
   # The above line generates a compile time syntax error.
   ...
}

$TransRef is a reference to an array of references to arrays. I am trying to process each element in the array pointed to by $TransRef. $TransArrRef should obtain a reference to an array. I want to assign the first value within that array to $TransID. But, this statement generates a compile syntax error.

I must be doing something wrong, but can not figure out what it is. Can anyone help?

perlmonks.org/?node=References+quick+reference

ysth
– ysth

2012-10-24 07:17:23 +00:00
Commented Oct 24, 2012 at 7:17 — ysth
– ysth, Commented Oct 24, 2012 at 7:17

RobEarl · Accepted Answer · 2012-10-24 07:16:05Z

4

The syntax error is coming from $$#TransRef which should be $#$TransRef. By misplacing the # you accidentally commented out the rest of the line leaving:

for ($Loop = 0; $Loop <= $$
{
   $TransArrRef = $$TransRef[$Loop];
   ...
}

$$ is ok under strict as it gives you the process id leaving the compiler to fail further down.

Also, $#$TransRef gives you the last element in the array so you'd need <= rather than just <. Or use this Perl style loop:

for my $loop (0 .. $#$TransRef) {
    $TransID = $TransRef->[$loop]->[0];
    #   ...
}

edited Oct 24, 2012 at 7:16

answered Oct 24, 2012 at 6:38

RobEarl

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1 Comment

ysth Over a year ago

there's also an error in my $TransRef = @_; which will assign a number (the number of elements in @_) to $TransRef

Pavel Vlasov · Accepted Answer · 2012-10-24 06:42:13Z

2

my $arrays_ref = [ [1,2], [3,4] ];

for my $array_ref (@$arrays_ref) {

    printf "%s\n", $array_ref->[0];
}

answered Oct 24, 2012 at 6:42

Pavel Vlasov

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Comments

TLama · Accepted Answer · 2014-03-05 16:01:46Z

0

You can use foreach as well:

my @array = ('val1', 'val2', 'val3') ;
my $array_ref = \@array ;

print "array size is $#{$array_ref} \n" ;

foreach $elem (@$array_ref) {
   print "$elem \n"
}

Outputs:

array size is 2 
val1 
val2 
val3

edited Mar 5, 2014 at 16:01

TLama

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answered Mar 5, 2014 at 15:42

user2275693

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