perl - How Can I Remove Magic Number when using XML::Simple? -

i did exercise this, how calculate # of xml elements collapsed array xml::simple don't have hard-code # of elements? plan use code parse bigger xml file. don't want cout elements manual.

can use count replace magic numbers, little person.count or hobbie.length etc. know, can use kind of statement in c# conveniently.

#!/usr/bin/perl -w use strict; use xml::simple; use data::dumper;  $tree = xmlin('./t1.xml');  print dumper($tree); print "\n"; (my $i = 0; $i < 2; $i++) # magic number '2' {     print "$tree->{person}->[$i]->{first_name} $tree->{person}->[$i]->{last_name}\n";     print "\n";     (my $j = 0; $j < 3; $j++) # magic number '3'     {         print $tree->{person}->[$i]->{hobbie}->[$j], "\n";     }     print "\n"; } 

out put:

could not find parserdetails.ini in c:/perl/site/lib/xml/sax $var1 = {           'person' => [                       {                         'hobbie' => [                                     'bungy jumping',                                     'sky diving',                                     'knitting'                                   ],                         'last_name' => 'bloggs',                         'first_name' => 'joe'                       },                       {                         'hobbie' => [                                     'swim',                                     'bike',                                     'run'                                   ],                         'last_name' => 'liu',                         'first_name' => 'jack'                       }                     ]         };  joe bloggs  bungy jumping sky diving knitting  jack liu  swim bike run 

my xml source file below

<document>   <person>     <first_name>joe</first_name>     <last_name>bloggs</last_name>     <hobbie>bungy jumping</hobbie>     <hobbie>sky diving</hobbie>     <hobbie>knitting</hobbie>   </person>   <person>     <first_name>jack</first_name>     <last_name>liu</last_name>     <hobbie>swim</hobbie>     <hobbie>bike</hobbie>     <hobbie>run</hobbie>   </person> </document> 

since xml::simple produce array you, it's easy count length.

e.g. $tree->{person} array - or rather array reference (make sure it's 1 using forcearray option of xml::simple if there's 1 person).

• you can length first de-referencing array (using @{} array de-reference): @{ $tree->{person} }

• then use resulting array in scalar context evaluates # of elements in array (in other words, a.lenth/a.count functions in other languages translate perl idiom scalar(@a) scalar() function optional if scalar context applies).

  in case, numeric comparison operator "<" force scalar context, if not case have used scalar() function.

example:

# don't forget forcearray option of xml::simple ensure person , hobbie array refs (my $i = 0; $i < scalar( @{ $tree->{person} } ); $i++) { # scalar() optional here     print "$tree->{person}->[$i]->{first_name} $tree->{person}->[$i]->{last_name}\n";     print "\n";     (my $j = 0; $j < @{ $tree->{person}->[$i]->{hobbie} }; $j++) {         print $tree->{person}->[$i]->{hobbie}->[$j], "\n";     }     print "\n"; } 

as note, different method of counting length of perl array $#a construct, returns the index of last element of array - e.g. 1 less amount of elements in array. i'm not aware of performance difference between using 2 approaches, if find both equally readable, use them appropriate (e.g. if need index of last element, use $#a; if # of elements, use @a or scalar(@a) needed).

a reference perl data structures cookbook @perldoc