The following tables demonstrate behaviors for 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.
Σημείωση: 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().
Σημείωση: 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.
Πίνακας M-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 |
Πίνακας M-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 |
Πίνακας M-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.