The bool type only has two values, and is used to express a truth value. It can be either true or false.


To specify a bool literal, use the constants true or false. Both are case-insensitive.

= True; // assign the value TRUE to $foo

Typically, the result of an operator which returns a bool value is passed on to a control structure.

// == is an operator which tests
// equality and returns a boolean
if ($action == "show_version") {
"The version is 1.23";

// this is not necessary...
if ($show_separators == TRUE) {

// ...because this can be used with exactly the same meaning:
if ($show_separators) {

Converting to boolean

To explicitly convert a value to bool, use the (bool) cast. Generally this is not necessary because when a value is used in a logical context it will be automatically interpreted as a value of type bool. For more information see the Type Juggling page.

When converting to bool, the following values are considered false:

  • the boolean false itself
  • the integer 0 (zero)
  • the floats 0.0 and -0.0 (zero)
  • the empty string "", and the string "0"
  • an array with zero elements
  • the unit type NULL (including unset variables)
  • Internal objects that overload their casting behaviour to bool. For example: SimpleXML objects created from empty elements without attributes.

Every other value is considered true (including resource and NAN).


-1 is considered true, like any other non-zero (whether negative or positive) number!

((bool) ""); // bool(false)
var_dump((bool) "0"); // bool(false)
var_dump((bool) 1); // bool(true)
var_dump((bool) -2); // bool(true)
var_dump((bool) "foo"); // bool(true)
var_dump((bool) 2.3e5); // bool(true)
var_dump((bool) array(12)); // bool(true)
var_dump((bool) array()); // bool(false)
var_dump((bool) "false"); // bool(true)