Booleans

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

Syntax

To specify a boolean 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 boolean value is passed on to a control structure.


<?php
// == 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 boolean, 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 boolean argument.

See also Type Juggling.

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

the boolean FALSE itself
the integers 0 and -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 empty tags

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

Warning

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


<?php
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)
?>