Specifications

Testing Variable Status

PHP has several functions for testing the status of a variable.

The first of these is isset(), which has the following prototype:

int isset(mixed var);

This function takes a variable name as argument and returns true if it exists and false other-

wise.

You can wipe a variable out of existence by using its companion function, unset(). This has

the following prototype:

int unset(mixed var);

This gets rid of the variable it is passed and returns true.

Finally there is empty(). This checks to see if a variable exists and has a non-empty, non-zero

value and returns true or false accordingly. It has the following prototype:

int empty(mixed var);

Let’s look at an example using these three functions.

Try adding the following code to your script temporarily:

echo isset($tireqty);

echo isset($nothere);

echo empty($tireqty);

echo empty($nothere);

Refresh the page to see the results.

The variable

$tireqty should return true from isset() regardless of what value you entered or

didn’t enter in that form field. Whether it is

empty() or not depends on what you entered in it.

The variable $nothere does not exist, so it will generate a false result from isset() and a

true result from empty().

These functions can be handy in making sure that the user filled out the appropriate fields in

the form.

Reinterpreting Variables

You can achieve the equivalent of casting a variable by calling a function. The three functions

that can be useful for this are

int intval(mixed var);

double doubleval(mixed var);

string strval(mixed var);

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