关于PHP if($x),==,===判断比较的官方说明

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.

$x gettype() empty() is_null() isset() boolean Comparisons of with PHP functions Expression : if($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

TRUE FALSE NULL Loose comparisons with ==   1 0 -1 “1″ “0″ “-1″ array() “php” “”

TRUE

TRUE

FALSE

TRUE

FALSE

TRUE

TRUE

FALSE

TRUE

FALSE

FALSE

TRUE

FALSE

FALSE

FALSE

TRUE

FALSE

TRUE

FALSE

FALSE

TRUE

FALSE

TRUE

TRUE

FALSE

TRUE

1

TRUE

FALSE

TRUE

FALSE

FALSE

TRUE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

0

FALSE

TRUE

FALSE

TRUE

FALSE

FALSE

TRUE

FALSE

TRUE

FALSE

TRUE

TRUE

-1

TRUE

FALSE

FALSE

FALSE

TRUE

FALSE

FALSE

TRUE

FALSE

FALSE

FALSE

FALSE

“1″

TRUE

FALSE

TRUE

FALSE

FALSE

TRUE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

“0″

FALSE

TRUE

FALSE

TRUE

FALSE

FALSE

TRUE

FALSE

FALSE

FALSE

FALSE

FALSE

“-1″

TRUE

FALSE

FALSE

FALSE

TRUE

FALSE

FALSE

TRUE

FALSE

FALSE

FALSE

FALSE

NULL

FALSE

TRUE

FALSE

TRUE

FALSE

FALSE

FALSE

FALSE

TRUE

TRUE

FALSE

TRUE

array()

FALSE

TRUE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

TRUE

TRUE

FALSE

FALSE

“php”

TRUE

FALSE

FALSE

TRUE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

TRUE

FALSE

“”

FALSE

TRUE

FALSE

TRUE

FALSE

FALSE

FALSE

FALSE

TRUE

FALSE

FALSE

TRUE

TRUE FALSE NULL Strict comparisons with ===   1 0 -1 “1″ “0″ “-1″ array() “php” “”

TRUE

TRUE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

TRUE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

1

FALSE

FALSE

TRUE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

0

FALSE

FALSE

FALSE

TRUE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

-1

FALSE

FALSE

FALSE

FALSE

TRUE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

“1″

FALSE

FALSE

FALSE

FALSE

FALSE

TRUE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

“0″

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

TRUE

FALSE

FALSE

FALSE

FALSE

FALSE

“-1″

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

TRUE

FALSE

FALSE

FALSE

FALSE

NULL

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

TRUE

FALSE

FALSE

FALSE

array()

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

TRUE

FALSE

FALSE

“php”

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

TRUE

FALSE

“”

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

FALSE

TRUE

官方地址：http://www.php.net/manual/en/types.comparisons.php