This is the simplest type. A bool expresses 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) or (boolean) casts. However, in most cases the cast is unnecessary, since a value will be automatically converted if an operator, function or control structure requires a bool argument.

See also Type Juggling.

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 special type NULL (including unset variables)
  • SimpleXML objects created from attributeless empty elements, i.e. elements which have neither children nor attributes.

Every other value is considered true (including any 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)