php session error_PHP tutorial

1.
Error message
Warning: Cannot send session cookie - headers already sent
Warning: Cannot send session cache limiter - headers already sent
Analysis and solution
This type of problem, The reason is that when you use session_start() in the program, 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 caused by the about in your php.ini session.save_path is not set properly. The solution is to set session.save_path and session.cookie_path to
session_save_path = c:temp
session.cookie_path = c:temp
and then in the c: directory Create a temp directory under
3.
Error prompt
Warning: Trying to destroy uninitialized session in
Analysis and solution
When such a prompt occurs, it is usually your fault Caused by 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 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 The same error as question 1, is it because I used session_start() before header?
Answer: Maybe you really checked your php program carefully, and there was indeed no error before referencing header(). Any 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 simplest method 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 session variable in the following page. Registered variable value. How to solve it?
Program fragment of the problem:
session_start();
$ok = 'love you';
session_register('ok');
header("location: next.php");
?>
next.php
session_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. There is still no detailed answer to the reason for this problem.
But there is a solution. As shown below
header("Location: next.php" ."?" . SID);
When jumping to the next page, use the current id of the session as a parameter and pass it to the next page. 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['username'];
?>
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 variable. However, it should be noted that if you use $HTTP_SESSION_VARS or $_SESSION to reference the session variable in the current page, then you may need to cooperate with unset() to unset the session variable.
And session_destroy() clears the current session environment. This means that after you use the session_destroy() function, it is no longer possible to use session_is_registered() to detect session variables. But it should be noted that it cannot clear the session in the global or use the session cookie. So before using session_destroy, it is best not to use $HTTP_SESSION_VARS $_SESSION to access the session. (Translated from php.net)
Routine:
if(isset($_COOKIE[session_name()])) {
session_start();
session_destroy();
unset($_COOKIE[session_name()]);
}
Reprinted.