Why Php Assumes No Session Started When It Has Been Started? - php

Question

Php Folks,
Why on the second-page load (same page), the ELSEIF does not trigger?
My Expectation:
On the 1st page load, the IF should trigger since there are no sessions at the beginning.
Then a session should start. Set to '$_SESSION['form_step'] = 'start'.
Finally, set to:
$_SESSION['form_step'] = 'end';
On the 2nd page load (same page reloaded), the ELSEIF should trigger since a session was started previously and set to: $_SESSION['form_step'] = 'end'.
if(!session_id() || $_SESSION['form_step'] != 'end')
{
session_start();
$_SESSION['form_step'] = 'start';
echo "Line: 28 "; echo "Session Step: "; echo $_SESSION['form_step']; echo "<br>";
echo "Line: 29 "; echo "New Session Id: "; echo session_id(); echo "<br>";
$_SESSION['form_step'] = 'end';
}
elseif($_SESSION['form_step'] == 'end')
{
echo "Line: 35 "; echo "Session Step: "; echo $_SESSION['form_step']; echo "<br>";
echo "Line: 36 "; echo "New Session Id: "; echo session_id(); echo "<br>";
}
Result:
On the second page-load or same page reload, even though a session exists, the ELSEIF doesn't trigger but the IF triggers instead as if there were no sessions in existence or no sessions were started previously or no sessions been started yet.
Why is that? When you test the code you will see:
On the 1st page load, the IF will trigger.
So far, so good.
But refreshing the page would result in the same IF getting triggered again instead of the ELSEIF!
Not good!
Puzzling. I am confused.
On every page reload, I get echoed the same:
Line: 28 Session Step: start
Line: 29 New Session Id: ri4pbr42623g9uoaiiq3ebr41r
EDIT 1
I edited code to following based on Alvaro Gonzales and Ben Foster advice:
<?php
error_reporting(E_ALL);
session_start();
if(!session_id() || session_id() != $session_id || $_SESSION['form_step'] != 'end')
{
session_start();
$_SESSION['form_step'] = 'start';
echo "Line: 28 "; echo "Session Step: "; echo $_SESSION['form_step']; echo "<br>";
echo "Line: 29 "; echo "New Session Id: "; echo session_id(); echo "<br>";
$_SESSION['form_step'] = 'end';
$session_id = session_id();
}
elseif($_SESSION['form_step'] == 'end') //Q2. WHY THIS IF GETS TRIGGERED WHEN CLICKING ANY NUMBERED PAGE LINKS (ON PAGINATION SECTION (EG PAGE 1 2 3 ETC.)) SINCE SESSION ID ALREADY EXISTS DUE TO ['form_step'] = 'end' ?
{
echo "Line: 35 "; echo "Session Step: "; echo $_SESSION['form_step']; echo "<br>";
echo "Line: 36 "; echo "New Session Id: "; echo session_id(); echo "<br>";
}
I now get this error:
Notice: Undefined variable: session_id in
C:\xampp\htdocs\power.page\pagination_test_SIMPLE.php on line 5
Notice: session_start(): A session had already been started - ignoring
in C:\xampp\htdocs\power.page\pagination_test_SIMPLE.php on line 7**
Along with the error, I get my echoes:
Line: 28 Session Step: start
Line: 29 New Session Id: s3sojmnogkhkmga43fhk1u2j17**
How to fix this without seeing errors?
NOTE: At the very 1st time the page loads, I need to the IF to get triggered so it finds no sessions and creates one.
Sets $_SESSION['form_step'] = 'start';
Then $_SESSION['form_step'] = 'end';
Then when I reload the page, I need PHP to find the $_SESSION['form_step'] == 'end' and trigger the IFELSE and not the same IF again.
Why I need the ELSEIF triggered on the page reload? is because when the page is reloaded I need task 2 to trigger. While when the page is loaded for the 1st time I need task 1 to trigger.
IF deals with task 1. ElseIF deals with task 2.
This is a complex script. I only gave a relevant snippet here.
EDIT 2
If I leave the IF to this:
if(!session_id())
Then the IF never triggers. Always the ELSE.
I need the IF to trigger on the very 1st time the page loads and initiate the session and do the 1st task.
Then as long as the session exists, on every page refresh/reload, I need the ELSEIF to trigger to do the 2nd task.
This code doesn't work ...
<?php
error_reporting(E_ALL);
session_start();
if(!session_id())
{
session_start();
$_SESSION['form_step'] = 'start';
echo "Line: 28 "; echo "Session Step: "; echo $_SESSION['form_step']; echo "<br>";
echo "Line: 29 "; echo "New Session Id: "; echo session_id(); echo "<br>";
$_SESSION['form_step'] = 'end';
$session_id = session_id();
}
elseif($_SESSION['form_step'] == 'end')
{
echo "Line: 35 "; echo "Session Step: "; echo $_SESSION['form_step']; echo "<br>";
echo "Line: 36 "; echo "New Session Id: "; echo session_id(); echo "<br>";
}

Answer 1

session_start() needs to be called before attempting to access any session variable, even when refreshing the page.
So when refreshing the page, a session is not currently active. Hence your if statement evaluates to true.
Try moving session_start() to the top of your file.

Answer 2

What you are trying to do is very unclear to me. But this should work (based on my understanding of the expected behavior).
error_reporting(E_ALL);
session_start();
if (!isset($_SESSION['form_step']) || $_SESSION['form_step'] !== 'end') {
// This will be overwrited before the end of this page load.
$_SESSION['form_step'] = 'start';
echo "Line: ".__LINE__;
echo "Session Step: ";
echo $_SESSION['form_step'];
echo "<br>";
echo "Line: ".__LINE__;
echo "New Session Id: ";
echo session_id();
echo "<br>";
$_SESSION['form_step'] = 'end';
// This variable is never used, you might want to get rid of it.
$session_id = session_id();
} else {
echo "Line: ".__LINE__;
echo "Session Step: ";
echo $_SESSION['form_step'];
echo "<br>";
echo "Line: ".__LINE__;
echo "New Session Id: ";
echo session_id();
echo "<br>";
}