php man page for debug_zval_dump

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)