PHP: Booleans - Manual

Booleans

This is the simplest 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 the keywords TRUE or FALSE. Both are case-insensitive.


<?php

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

?>

Typically, some kind of operator which returns a boolean value, and the value is passed on to a control structure.


<?php

// == 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 "<hr>\n";

}



// ...because instead, this can be used:

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 unncecessary, 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!


<?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)

?>