Booleans

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

Syntax

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

<?php
$foo = 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.

<?php
$action = "show_version";
$show_separators = true;

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

// this is not necessary...
if ($show_separators == TRUE) {
    echo "<hr>\n";
}

// ...because this can be used with exactly the same meaning:
if ($show_separators) {
    echo "<hr>\n";
}
?>

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, or GMP objects representing the value 0.

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

Warning

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

Example #1 Casting to Boolean

<?php
var_dump((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)
?>