in reply to Re: print_r
in thread print_r

grinder:  This will recurse endlessly until the heat death of the universe or you run out of swap, whichever comes first. Then again, perhaps the PHP implementation does as well.

PHP's print_r (522) does indeed detect recursion after the first loop: 
<?php
 $r1 = array( 1 );
 $r2 = array( 2, &$r1 );
 array_push( $r1, &$r2 );

 print_r($r1);
?>

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This will result in the following output: 
(
    [0] => 1
    [1] => Array
        (
            [0] => 2
            [1] => Array
                (
                    [0] => 1
                    [1] => Array
 *RECURSION*
                )

        )

)

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Regards

mwa

Replies are listed 'Best First'.
Re^3: print_r
by Anonymous Monk on Mar 23, 2009 at 16:30 UTC
    recursion check: 
    sub print_r {
    
    my $level="";
    my @level_index=();
    my @print_r_Recursion=();
    print_rec (@_);
    undef @level_index;
    undef @print_r_Recursion;
    undef $level;
    
    sub print_rec {

        if ( ! defined $level ) { $level = 0 };
        if ( ! defined @level_index ) { $level_index[$level] = 0 };

        for ( @_ ) {

            my $element = $_;
            my $index   = $level_index[$level];
            
            if (ref($element) eq 'ARRAY' || ref($element) eq 'HASH'){
                my $loop=0;
                for (@print_r_Recursion){
                    if (($element."") eq ($_."")){
                        $loop=1;
                        last;
                    }
                }
                if ($loop==1){
                    print "\t" x $level . "[$index] =&gt; ". ref($elem
+ent) ." *recursion*\n";
                    next;
                }
                push @print_r_Recursion,$element;
            }
            
            print "\t" x $level . "[$index] =&gt; ";

            if ( ref($element) eq 'ARRAY' ) {
                my $array = $_;

                $level_index[++$level] = 0;

                print "(Array)\n";

                for ( @$array ) {
                    print_rec( $_ ); 
                }
                --$level if ( $level &gt; 0 );
            } elsif ( ref($element) eq 'HASH' ) {
                my $hash = $_;

                print "(Hash)\n";

                ++$level;

                for ( keys %$hash ) {
                    $level_index[$level] = $_;
                    print_rec( $$hash{$_} );
                }
            } else {
                print "$element\n";
            }

            $level_index[$level]++;
        }
    }
}

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In Section Cool Uses for Perl