isset - how do you explain everything it does?

[whatson]

I kind of get isset function, but not entirely.
I understand it is mainly used with if statements.
Is it just for submitting forms? And what is the difference for isset with GET and POST?

If I use it for GET
e.g. if(isset($_GET['page']))
Does this check the url to see if there is a value for page?

And for POST, does it just mean, if the form submit button is clicked?

[londrum]

it's possible to set (or overwrite) a GET variable or a POST variable in your script, just be writing

$_GET['page'] = 'blah';

$_POST['page'] = 'blah';

so they don't have to come from a URL or a form (although they usually do).

i think isset just checks whether a variable exists. it doesn't care where it came from.

[whatson]

Oh, so it just checks if a variable exists, that makes sense.

[g1smd]

IF "IS SET" (binary answer: yes/no) THEN...

[MinosTheNinth]

In case testing $_GET['page'] it only test that variable exists (as answered above). But it does not test if variable has value. From isset point of view there is no difference between ?page and ?page=index

If you want to test that variable has some data, you can use empty() - [php.net...]

[jadebox]

Isset returns false if the specified variable (or array element) has not been defined or if it has been defined but was assigned a value of null.

Isset is not a function. It is a "language construct." It sounds like I'm being pendantic to point it out, but it is important to know because you can't, for example, reference it as a variable function or pass it to a method expecting a function.

-- Roger