Booleans

This is the easiest type. A boolean expresses a truth value. It can be either TRUE or FALSE.

Note: The boolean type was introduced in PHP 4.

Syntax
To specify a boolean literal, use either the keyword TRUE or FALSE. Both are case-insensitive.

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

Usually you use some kind of operator which returns a boolean value, and then pass it on to a control structure.

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

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

---

\n";
}

// ...because you can simply type
if ($show_separators) {
echo "

---

\n";
}
?>

Converting to boolean
To explicitly convert a value to boolean, use either the (bool) or the (boolean) cast. However, in most cases you do not need to use the cast, since a value will be automatically converted if an operator, function or control structure requires a boolean argument.

See also Type Juggling.

When converting to boolean, the following values are considered FALSE:

the boolean FALSE itself
the integer 0 (zero)
the float 0.0 (zero)
the empty string, and the string "0"
an array with zero elements
an object with zero member variables (PHP 4 only)
the special type NULL (including unset variables)
SimpleXML objects created from empty tags
Every other value is considered TRUE (including any resource).
Warning
-1 is considered TRUE, like any other non-zero (whether negative or positive) number!


var_dump((bool) ""); // 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)
?>