[RESOLVED] How to best prepare for Cold Calls

ATS16805

I don't know the proper term, so i can only try to describe it...

the idea of someone accessing a URL which leads directly to a page from the "middle" of one of your apps-- instead of the start of the app where the user would begin to complete text input, etc.

My instinct to code for this is probably not far from what most of you would do in this situation, and i've received advice about this before-- but, i've never been confident by my understanding of these similar but different Variable Handling Functions.

discourse i'm hoping for here is to get a better understanding of the purposeful useage of the following (or at least one of the following functions)

isset()
empty()
defined()

if someone will humor me, maybe we'd start off w/ isset()

i see that i've used this in the past, and, supplemental to reading at php.net, i likely received instruction here to use it as so, yet it still seems unclear -- because of when i've seen in practice, so...

 if (isset($variable, variable2, variable3, $_POST['var_one'])

am i right to say that here, we use isset to check whether the variable holds data, and in the case that it doesn't, isset prevents the "Undefined Constant" error? i realize it either returns TRUE or FALSE-- but... Why do we care? i mean-- why not just use something like

if ($var > '') { do something } else { do something else

does that not check for a value in the $var, and it would seem even more versatile as we get to define the actions if true or false w/ the regular variable.

i was in the habit of using if (empty($_POST['my_name_field']) {

or if (!empty($_POST[... etc , but i see isset() used more often, so this is primarily why i feel i just don't get it. i have definitely thrown more errors w/ isset() than i have w/ empty()

sorry if this is really laughable, but it's difficult for me to perceive the important, key differences here-- and when and why one is used instead of the other.

thanks!

thorpe

isset() checks for the existence of a variable, not if that variable holds a value.

<?php

  $a = '';
  if (isset($a)) {
    echo "a is set";
  }

  if (empty($a)) {
    echo "a is empty";
  }

?>

ATS16805

rrriiiigt. okay. so, it really comes down to the situation then-- because either could possibly be the preferred method for using, as i described above, to handle the URI being accessed directly from "outside" of the application flow. would you agree, or is one or the other always the better choice?

okay... here's where i get confused:
using isset(), we test if the variable exists - result: TRUE
hmm...
(tries using his "know what you know" theory of conditional logic which he learned from some book in attempt to eliminate needless elseif or else's...)
i suppose a direct call w/ an absolute url will always return false, no matter what, so we can make the decision based on that info alone every time-- unless there's an error in the app in which the page has been mistakenly directed to the page w/ this function. would that be fair to say is true also?

how are $_SESSION affected by this?

your presentation definitely helped thorpe. to have a skewed perception of isset(), as i obviously did, quite simply is dangerous! i try to avoid that (meaning, a cursory understanding, i try to avoid) whenever possible... i guess, hence my inquiry! 🙂

thorpe

i suppose a direct call w/ an absolute url will always return false, no matter what,

Im not 100% sure Im with you. Are you trying to protect pages that should only be accessed when requested by a form for instance?

if (isset($_POST['input'])) {
  // process.
} else {
  // reject request.
}

In this example, $_POST['input'] simply will not exist (will not be set) unless the page is requested by a form.

However, in allot of cases, you would want more than the form to simply have been submiitted. You'll want it to have a value. In this situation, empty() is often a better choice.

if (!empty($_POST['input'])) {
  // form was submitted and contains a value.
} else {
  // form not submitted OR contains no value.
}

Note that empty() will return true if the value it is testing is false.

empty() and isset() work exactly the same with sessions.

Still not sure where your questions are going exactly.

ATS16805

...It seems that no combination of isset() and / or empty() gives me what i'm striving for...

ATS16805

:bump:

turns out that this whole time... nothing would work because i had a stray $ floating around in just the right spot, apparently. i left this that day, and came back last night to find that a fresh look, looking for ANYTHING that might be wrong, NOT JUST LOGIC in this case, was the best solution i could ever have tried!

thanks to Thorpe for helping me to really see isset() and empty() in a very practical light.
it all makes perfect sense now, and i see the logic of the function more clearly, whereas i was previously using one or the other based on circumstances not quite what i should have been.

RDFrame

Think of it like this. When checking the value of a variable, PHP actually accesses that variable, whereas with isset() PHP checks if that variable can be accessed (ie. has already been defined).