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
    // == 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.

    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!

    <?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)
    ?>

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