Question

Can anyone tell me where I am wrong? I can’t figure it out….
Basically what my code is trying to do is to read the files and create a hash for each file, these hashes are organized into on hash. The user would input two parameters, one is the key of the outer hash, and the other is for the one inside.
The ones I input are city and PIT; the same as the parameter I wrote before the line that breaks down….

I tried thousands of times, I keep getting this error: Can’t use an undefined value as a HASH reference I have commented that line out in the code.
The two files are cities.txt; school.txt.
Their content are just as below:
PIT\tPittsburgh
NY\tNewYork

#!/bin/perl -w
use strict;
use Data::Dumper;
our %hash_all = ();
sub readHash{
    my @vars = @_;
    my $filename = $vars[0];
    my %iptable = ();
    if(open(IN,$filename.".txt")) {
            while(<IN>) {   
            my @tmp = split(/\t/);
            $iptable{$tmp[0]} = $tmp[1];
        }
    }
    return %iptable;
}

sub loadAll{
        my %school = readHash("school");
    my %city = readHash("cities");
    $hash_all{school} = \%school;
    $hash_all{city} = \%city;
    print Dumper(\%hash_all);
}

 sub queryValue{
    my @pars = @_;
    my $key1 = $pars[0];
    my $key2 = $pars[1];

    print "key1".$key1;
    print "key2".$key2;
    print Dumper(\%hash_all);   
    my %temp = %{$hash_all{"city"}};#THIS LINE WORKS
    print $temp{"PIT"}; #THIS LINE WORKS
    my %temp2 = %{$hash_all{$key1}};#THIS LINE HAS AN ERROR
    print $temp2{$key2};
}

loadAll();
my $par1 = <>;
my $par2 = <>;
queryValue($par1,$par2);

Answer 1

Your problem is probably that when you read in $par1 and $par2, they include newlines at the end. So you end up looking for a hash key like "city\n", which is not the same as "city".

Make sure you use chomp on your input parameters, like chomp($par1) . That should take care of it.