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.

Note: Some numeric operations can result in a value represented by the constant NAN . Any loose or strict comparisons of this value against any other value, including itself, but except TRUE , will have a result of FALSE . (i.e. NAN != NAN and NAN !== NAN ) Examples of operations that produce NAN include sqrt(-1) , asin(2) , and acosh(0) .

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 = array('a', 'b'); array FALSE FALSE TRUE TRUE $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

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 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