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.
To specify a boolean-literal, use either the keyword TRUE or FALSE. Both are case-insensitive.
Usually you use some kind of operator which returns a boolean value, and then pass it on to a control structure.
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
the integer 0 (zero)
the double 0.0 (zero)
an array with zero elements
an object with zero elements
the special value NULL
Warning |
-1 is considered TRUE, like any other non-zero (whether negative or positive) number! |