Recipe 4.6 Iterating Over an Array by Reference

4.6.1 Problem

You have a reference to an array, and you want to use a loop to work with the array's elements.

4.6.2 Solution

Use foreach or for to loop over the dereferenced array:

# iterate over elements of array in $ARRAYREF foreach $item (@$ARRAYREF) {     # do something with $item } for ($i = 0; $i <= $#$ARRAYREF; $i++) {     # do something with $ARRAYREF->[$i] }

4.6.3 Discussion

The solutions assume you have a scalar variable containing the array reference. This lets you do things like this:

@fruits = ( "Apple", "Blackberry" ); $fruit_ref = \@fruits; foreach $fruit (@$fruit_ref) {     print "$fruit tastes good in a pie.\n"; } Apple tastes good in a pie. Blackberry tastes good in a pie.

We could have rewritten the foreach loop as a for loop like this:

for ($i=0; $i <= $#$fruit_ref; $i++) {     print "$fruit_ref->[$i] tastes good in a pie.\n"; }

Frequently, though, the array reference is the result of a more complex expression. Use the @{ EXPR } notation to turn the result of the expression back into an array:

$namelist{felines} = \@rogue_cats; foreach $cat ( @{ $namelist{felines} } ) {     print "$cat purrs hypnotically..\n"; } print "--More--\nYou are controlled.\n";

Again, we can replace the foreach with a for loop:

for ($i=0; $i <= $#{ $namelist{felines} }; $i++) {     print "$namelist{felines}[$i] purrs hypnotically.\n"; }

4.6.4 See Also

perlref(1) and perllol(1); Chapter 8 of Programming Perl; Recipe 11.1; Recipe 4.5



Perl Cookbook
Perl Cookbook, Second Edition
ISBN: 0596003137
EAN: 2147483647
Year: 2003
Pages: 501

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