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Appendix O. PHP type comparison tables

The following tables demonstrate behaviors of PHP types and comparison operators, for both loose and strict comparisons. This supplemental is also related to the manual section on type juggling. Inspiration was provided by various user comments and by the work over at BlueShoes.

Before utilizing these tables, it's important to understand types and their meanings. For example, "42" is a string while 42 is an integer. FALSE is a boolean while "false" is a string.

Note: HTML Forms do not pass integers, floats, or booleans; they pass strings. To find out if a string is numeric, you may use is_numeric().

Note: Simply doing if ($x) while $x is undefined will generate an error of level E_NOTICE. Instead, consider using empty() or isset() and/or initialize your variables.

Table O-1. Comparisons of $x with PHP functions

Expression	gettype()	empty()	is_null()	isset()	boolean : `if($x)`
`$x = "";`	string	`TRUE`	`FALSE`	`TRUE`	`FALSE`
`$x = NULL`	NULL	`TRUE`	`TRUE`	`FALSE`	`FALSE`
`var $x;`	NULL	`TRUE`	`TRUE`	`FALSE`	`FALSE`
`$x` is undefined	NULL	`TRUE`	`TRUE`	`FALSE`	`FALSE`
`$x = array();`	array	`TRUE`	`FALSE`	`TRUE`	`FALSE`
`$x = false;`	boolean	`TRUE`	`FALSE`	`TRUE`	`FALSE`
`$x = true;`	boolean	`FALSE`	`FALSE`	`TRUE`	`TRUE`
`$x = 1;`	integer	`FALSE`	`FALSE`	`TRUE`	`TRUE`
`$x = 42;`	integer	`FALSE`	`FALSE`	`TRUE`	`TRUE`
`$x = 0;`	integer	`TRUE`	`FALSE`	`TRUE`	`FALSE`
`$x = -1;`	integer	`FALSE`	`FALSE`	`TRUE`	`TRUE`
`$x = "1";`	string	`FALSE`	`FALSE`	`TRUE`	`TRUE`
`$x = "0";`	string	`TRUE`	`FALSE`	`TRUE`	`FALSE`
`$x = "-1";`	string	`FALSE`	`FALSE`	`TRUE`	`TRUE`
`$x = "php";`	string	`FALSE`	`FALSE`	`TRUE`	`TRUE`
`$x = "true";`	string	`FALSE`	`FALSE`	`TRUE`	`TRUE`
`$x = "false";`	string	`FALSE`	`FALSE`	`TRUE`	`TRUE`

Table O-2. Loose comparisons with ==

	`TRUE`	`FALSE`	`1`	`0`	`-1`	`"1"`	`"0"`	`"-1"`	`NULL`	`array()`	`"php"`
`TRUE`	`TRUE`	`FALSE`	`TRUE`	`FALSE`	`TRUE`	`TRUE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`TRUE`
`FALSE`	`FALSE`	`TRUE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`TRUE`	`TRUE`	`FALSE`
`1`	`TRUE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`
`0`	`FALSE`	`TRUE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`TRUE`	`FALSE`	`TRUE`
`-1`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`
`"1"`	`TRUE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`
`"0"`	`FALSE`	`TRUE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`
`"-1"`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`
`NULL`	`FALSE`	`TRUE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`	`TRUE`	`FALSE`
`array()`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`	`TRUE`	`FALSE`
`"php"`	`TRUE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`

Table O-3. Strict comparisons with ===

	`TRUE`	`FALSE`	`1`	`0`	`-1`	`"1"`	`"0"`	`"-1"`	`NULL`	`array()`	`"php"`
`TRUE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`
`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`
`1`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`
`0`	`FALSE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`
`-1`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`
`"1"`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`
`"0"`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`
`"-1"`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`	`FALSE`
`NULL`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`	`FALSE`
`array()`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`	`FALSE`
`"php"`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`FALSE`	`TRUE`

PHP 3.0 note: The string value "0" was considered non-empty in PHP 3, this behavior changed in PHP 4 where it's now seen as empty.

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Copyright � 1997 - 2007 by the PHP Documentation Group. This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v1.0 or later. A copy of the Open Publication License is distributed with this manual, the latest version is presently available at http://www.opencontent.org/openpub/. Please see full copyright text at http://www.php.net/manual/en/copyright.php Original version of the above documentation is available at http://www.php.net/manual/en/

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