php man page for empty

EMPTY(3)								 1								  EMPTY(3)

empty - Determine whether a variable is empty

SYNOPSIS
       bool empty (mixed  $var)

DESCRIPTION
	Determine  whether a variable is considered to be empty. A variable is considered empty if it does not exist or if its value equals FALSE.
       empty(3) does not generate a warning if the variable does not exist.

PARAMETERS
	      o $var
		- Variable to be checked

	      Note

		      Prior to PHP 5.5, empty(3) only supports variables; anything else will result in a parse error. In other words, the  follow-
		     ing will not work: empty(trim($name)). Instead, use trim($name) == false.

	       No  warning  is generated if the variable does not exist. That means empty(3) is essentially the concise equivalent to !isset($var)
	      || $var == false.

RETURN VALUES
	Returns FALSE if $var exists and has a non-empty, non-zero value. Otherwise returns TRUE.

	The following things are considered to be empty:

	      o "" (an empty string)

	      o 0 (0 as an integer)

	      o 0.0 (0 as a float)

	      o "0" (0 as a string)

	      o NULL

	      o FALSE

	      o array() (an empty array)

	      o $var; (a variable declared, but without a value)

CHANGELOG
       +--------+---------------------------------------------------+
       |Version |						    |
       |	|						    |
       |	|		     Description		    |
       |	|						    |
       +--------+---------------------------------------------------+
       | 5.5.0	|						    |
       |	|						    |
       |	| empty(3) now supports  expressions,  rather  than |
       |	| only variables.				    |
       |	|						    |
       | 5.4.0	|						    |
       |	|						    |
       |	|  Checking  non-numeric offsets of strings returns |
       |	| TRUE. 					    |
       |	|						    |
       +--------+---------------------------------------------------+
EXAMPLES
       Example #1

	       A simple empty(3) / isset(3) comparison.

	      <?php
	      $var = 0;

	      // Evaluates to true because $var is empty
	      if (empty($var)) {
		  echo '$var is either 0, empty, or not set at all';
	      }

	      // Evaluates as true because $var is set
	      if (isset($var)) {
		  echo '$var is set even though it is empty';
	      }
	      ?>

       Example #2

	      empty(3) on String Offsets

	       PHP 5.4 changes how empty(3) behaves when passed string offsets.

	      <?php
	      $expected_array_got_string = 'somestring';
	      var_dump(empty($expected_array_got_string['some_key']));
	      var_dump(empty($expected_array_got_string[0]));
	      var_dump(empty($expected_array_got_string['0']));
	      var_dump(empty($expected_array_got_string[0.5]));
	      var_dump(empty($expected_array_got_string['0.5']));
	      var_dump(empty($expected_array_got_string['0 Mostel']));
	      ?>

	      Output of the above example in PHP 5.3:

	      bool(false)
	      bool(false)
	      bool(false)
	      bool(false)
	      bool(false)
	      bool(false)

	      Output of the above example in PHP 5.4:

	      bool(true)
	      bool(false)
	      bool(false)
	      bool(false)
	      bool(true)
	      bool(true)

NOTES
       Note

	      Because this is a language construct and not a function, it cannot be called using variable functions.

       Note

	       When using empty(3) on inaccessible object properties, the __isset() overloading method will be called, if declared.

SEE ALSO
       isset(3), __isset(), unset(3), array_key_exists(3), count(3), strlen(3), The type comparison tables.

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