Unclear pointer and array Post: 302884213

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LEARN ABOUT DEBIAN

devel::refcount

Devel::Refcount(3pm)					User Contributed Perl Documentation				      Devel::Refcount(3pm)

NAME

       "Devel::Refcount" - obtain the REFCNT value of a referent

SYNOPSIS

	use Devel::Refcount qw( refcount );

	my $anon = [];

	print "Anon ARRAY $anon has " . refcount($anon) . " reference
";

	my $otherref = $anon;

	print "Anon ARRAY $anon now has " . refcount($anon) . " references
";

DESCRIPTION

       This module provides a single function which obtains the reference count of the object being pointed to by the passed reference value.

FUNCTIONS

   $count = refcount($ref)
       Returns the reference count of the object being pointed to by $ref.

COMPARISON WITH SvREFCNT
       This function differs from "Devel::Peek::SvREFCNT" in that SvREFCNT() gives the reference count of the SV object itself that it is passed,
       whereas refcount() gives the count of the object being pointed to. This allows it to give the count of any referent (i.e. ARRAY, HASH,
       CODE, GLOB and Regexp types) as well.

       Consider the following example program:

	use Devel::Peek qw( SvREFCNT );
	use Devel::Refcount qw( refcount );

	sub printcount
	{
	   my $name = shift;

	   printf "%30s has SvREFCNT=%d, refcount=%d
",
	      $name, SvREFCNT($_[0]), refcount($_[0]);
	}

	my $var = [];

	printcount 'Initially, $var', $var;

	my $othervar = $var;

	printcount 'Before CODE ref, $var', $var;
	printcount '$othervar', $othervar;

	my $code = sub { undef $var };

	printcount 'After CODE ref, $var', $var;
	printcount '$othervar', $othervar;

       This produces the output

		       Initially, $var has SvREFCNT=1, refcount=1
		 Before CODE ref, $var has SvREFCNT=1, refcount=2
			     $othervar has SvREFCNT=1, refcount=2
		  After CODE ref, $var has SvREFCNT=2, refcount=2
			     $othervar has SvREFCNT=1, refcount=2

       Here, we see that SvREFCNT() counts the number of references to the SV object passed in as the scalar value - the $var or $othervar
       respectively, whereas refcount() counts the number of reference values that point to the referent object - the anonymous ARRAY in this
       case.

       Before the CODE reference is constructed, both $var and $othervar have SvREFCNT() of 1, as they exist only in the current lexical pad. The
       anonymous ARRAY has a refcount() of 2, because both $var and $othervar store a reference to it.

       After the CODE reference is constructed, the $var variable now has an SvREFCNT() of 2, because it also appears in the lexical pad for the
       new anonymous CODE block.

PURE-PERL FALLBACK
       An XS implementation of this function is provided, and is used by default. If the XS library cannot be loaded, a fallback implementation in
       pure perl using the "B" module is used instead. This will behave identically, but is much slower.

	       Rate   pp   xs
	pp 225985/s   -- -66%
	xs 669570/s 196%   --

SEE ALSO

       o   Test::Refcount - assert reference counts on objects

AUTHOR

       Paul Evans <leonerd@leonerd.org.uk>

perl v5.14.2							    2011-11-15						      Devel::Refcount(3pm)