Appendix L. PHP type comparison tables
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.
Note: HTML Forms do not pass integers, floats, or booleans, they pass strings. To find out of 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 L-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 L-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 L-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 TRUEPHP 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.
