debug_zval_dump(3) [php man page]

DEBUG_ZVAL_DUMP(3)							 1							DEBUG_ZVAL_DUMP(3)

debug_zval_dump - Dumps a string representation of an internal zend value to output

SYNOPSIS

       void debug_zval_dump (mixed  $variable, [mixed  $...])

DESCRIPTION

	Dumps a string representation of an internal zend value to output.

PARAMETERS

	      o $variable
		- The variable being evaluated.

RETURN VALUES

	No value is returned.

EXAMPLES

       Example #1

	      debug_zval_dump(3) example

	      <?php
	      $var1 = 'Hello World';
	      $var2 = '';

	      $var2 =& $var1;

	      debug_zval_dump(&$var1);
	      ?>

	      The above example will output:

	      &string(11) "Hello World" refcount(3)

       Note

	      Beware the refcount

	       The  refcount  value  returned  by this function is non-obvious in certain circumstances. For example, a developer might expect the
	      above example to indicate a refcount of 2. The third reference is created when actually calling debug_zval_dump(3).

	       This behavior is further compounded when a variable is not passed to debug_zval_dump(3) by reference.  To  illustrate,  consider  a
	      slightly modified version of the above example:

	      Example #2

		     <?php
		     $var1 = 'Hello World';
		     $var2 = '';

		     $var2 =& $var1;

		     debug_zval_dump($var1); // not passed by reference, this time
		     ?>

		     The above example will output:

		     string(11) "Hello World" refcount(1)

	       Why refcount(1)? Because a copy of $var1 is being made, when the function is called.

	       This function becomes even more confusing when a variable with a refcount of 1 is passed (by copy/value):

	      Example #3

		     <?php
		     $var1 = 'Hello World';

		     debug_zval_dump($var1);
		     ?>

		     The above example will output:

		     string(11) "Hello World" refcount(2)

	       A refcount of 2, here, is extremely non-obvious. Especially considering the above examples. So what's happening?

	       When  a	variable has a single reference (as did $var1 before it was used as an argument to debug_zval_dump(3)), PHP's engine opti-
	      mizes the manner in which it is passed to a function. Internally, PHP treats $var1  like	a  reference  (in  that  the  refcount	is
	      increased  for  the  scope of this function), with the caveat that if the passed reference happens to be written to, a copy is made,
	      but only at the moment of writing. This is known as "copy on write."

	       So, if debug_zval_dump(3) happened to write to its sole parameter (and it doesn't), then a copy would  be  made.  Until	then,  the
	      parameter remains a reference, causing the refcount to be incremented to 2 for the scope of the function call.

SEE ALSO

       var_dump(3), debug_backtrace(3), References Explained, References Explained (by Derick Rethans).

PHP Documentation Group 													DEBUG_ZVAL_DUMP(3)

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)