session_start();

For the session function of PHP, I have never been able to find a suitable answer, especially some errors and some error-free results. The most terrifying thing is the latter, which has always been a embarrassment for many beginners. Even some veterans are confused sometimes. This article makes a simple summary of these issues for everyone’s reference.

1.
Error message
Warning: Cannot send session cookie - headers already sent
Warning: Cannot send session cache limiter - headers already sent
Analysis and solution
The reason for this type of problem is that you use PHP in the program When session_start(), actual html content has been output before. Maybe you say, I don't have it, I just echo or print a message. Sorry, the output generated by your echo or print statement is the actual html content output. The way to solve this kind of problem is to move your session_start() to the first line of the program.

2.
Error message
Warning: open(F:/689phpsessiondatasess_66a39376b873f4daecf239891edc98b5, O_RDWR) failed
Analysis and solution
Such an error statement is usually because the session.save_path item in your php.ini is not set properly. The solution is to set session.save_path and session.cookie_path to
session_save_path = c: emp
session.cookie_path = c: emp
Then create a temp directory in the c: directory, you can

3.
Error message
Warning: Trying to destroy uninitialized session in
Analysis and solutions
Such a prompt is usually caused by you directly calling the session_destroy() function. Many friends think that the session_destroy() function can run independently, but this is not the case. The solution is to use PHP session_start() to enable the session function before you call the session_destroy() function.

4. Question: How to get the id value of the current session?
The easiest way is:
echo SID;
You will find out.

5. Question: My program does not have any output before calling the header function. Although I include a config.php file, there is no output in the config.php file. Why does the session still report something like Question 1 has the same error. Is it because I used PHP session_start() before the header?

Answer: Maybe you have carefully checked your php program, and there is indeed nothing before referencing header(). output, and there is no output in your include file! But do you use the cursor keys to move the check after the end statement of the PHP code?>? Then you will find that after ?>, there is a blank line or a few spaces. If you delete these blank lines or spaces, the problem will be solved.

Note: This problem will occur in PHP4.1.2 and higher versions, and has not been tested.

6. Question: After using session to log in to the main page, how can I use session to restrict login on other pages? . .
Answer: The easiest way is

session_start();

if(!session_registered
('login')
││$login!=true){

echo "You are not logged in";

exit;

}

7. Question: I used session_register() to register the session variable, but when I use header or JavaScript redirection statement, I cannot access the variable value registered by the session in the following page. How to solve it?
Program fragment of the question:

session_start();$ok='loveyou';session_register('ok');header("location:next.php");?>next.phpsession_start();echo$ ok;?>

Solution:
When you use functions such as header function or window.location, the session variable registered on your previous page will be easily lost. Regarding the cause of this problem, so far Still no detailed answer.
But there is a solution. As shown below
header("Location: next.php" ."?" . SID);
When jumping to the next page, the current ID of the session is used as a parameter and passed to the next page.

8. How to pass array in session

session_register
('data');

$data=array(1,2,3,4);

The method is to register first and then assign the value

9. Question 9: Can I use a method like $HTTP_GET_VARS['**'] to access the session value?

Answer: Yes, you can use the following global array to access the session to enhance the security of the web page
$HTTP_SESSION_VARS
$_SESSION
Routine:

session_start();

$username='stangly.
wrong' ;

session_register('
username');

echo$HTTP_SESSION_VARS
['username'];

echo'

';

echo$_SESSION
['user name'];

? >

Please refer to this routine to modify the program to suit your own needs.

Question 10: What is the difference between session_unregister() and session_destroy()? The main function of the
session_unregister() function is to unregister the current session. (Translated from php.net)

Routine:

if(isset($_COOKIE[session_name()])){session_start();session_destroy();unset($_COOKIE[session_name()]);}