======isset====== WMPRO, WMMINI FW >= 1.0 WMMEGA FW >= 2.0 Check if a variable exists ====Description==== int isset ( mixed $variable ) Determine if a variable is set ====Parameter==== $variable: Variable to check for existence((Multiple parameters are not supported as in mainline PHP)) ====Return Values==== Integer: 1 (true) if variable exists, 0 (false) if variable does not exist ====Examples====

====Notes==== There is no way to unset a variable once it has been set (except to exit the local scope or script where it was defined). Unlike mainline PHP, uPHP does not have a construct ''unset()'' or the constant ''null''. Unlike many other programming languages, you cannot simply remove a variable by setting it equal to nothing, such as by trying the statement ''$x=;''((As tested on a [[hardware:wattmons:WattmonPRO]] with firmware 1.1051 the statement ''$x=;'' causes a Watchdog Timeout error and a reboot of the Wattmon)). Also note that the uPHP [[isset()]] does not always generate a parsing error if the parameter is not a variable((See http://php.net/manual/en/function.isset.php where it says "Warning: isset() only works with variables as passing anything else will result in a parse error.")). All of these examples will return 0:

Although maybe useful in some situations, it is better not to use [[isset()]] for expressions or values instead of variables, because in some cases it //will// generate a parsing error. Example:

For the above example the parser answers:


Error on line 1: Undefined constant z
Error on line 1: Invalid function

Also note that in many situations where using [[uphp:control_structures:if]] to test for the existence of a variable it is possible to simplify the conditional test by using ''if($x)'' instead of ''if(isset($x))'' but only if you are certain that $x does not contain the value 0 (false). Unlike mainline PHP, uPHP does not generate an error for using ''if($x)'' on an undefined variable. Nevertheless, this is not a good practice even though this hack //is// commonly used //somewhat successfully// by Wattmon uPHP programmers. It is much better to use isset() if you are not certain that the variable has been initialized, and the code will be easier to understand later on. ====See Also==== [[is_int()]] - Check if a variable is an integer [[is_float()]] - Check if a variable is a float [[is_numeric()]] - Check if a value is numeric (int, float or numeric string) [[is_array()]] - Check if a variable is an array [[is_string()]] - Check if a variable is a string [[uphp:variables|uPHP Variable Types and Limits]]