如何通过Javascript将php会话从一页进行到另一页？

Question

I have a form (form.php) that uses the following JS code in the header:

<script type="text/javascript">
$(document).ready(function(){
$("a").click(function(){

$.post('test.php', function(data) {
        $('#test').html(data);
    });
    });
});
</script>

A have a link in form.php that once clicked I want a drop down to appear (without refreshing the page) eg "Display drop down". The code in the drop down is managed in test.php.

Test.php pulls data in from another service. In order to do get this data I use data that is kept in the session eg $_SESSION['data_that_is_sent_to_another_service'].

I start the session in form.php but in order for the test.php to get the information from the other service I need to start a session at the start of test.php.

The code works, but I then get a warning saying:

Warning: session_start() [function.session-start]:
Cannot send session cache limiter - headers already sent
(output started at /..my directory.../test.php:1) in /...my directory.../hrdeals.php on line 4

How can I get this warning not to appear (without turning off warnings in PHP)?

Any help much appreciated.

Gregor

PS - the JS might not be correct, but it's more the SESSION issue that I can solve

Answer 1

session_start() must be called before outputing anything to the browser. Check test.php and make sure there is no output.

Answer 2

1. Javascript and PHP Sessions have nothing to do with one another. Javascript lives in its little bubble (client side rendering/processing). PHP lives in its bubble (server side processing/output).

2. The error you get is (briefly) - headers already sent.

This refers to http headers (not the head tag where you may have some javascript). You can see the whole list here: http://en.wikipedia.org/wiki/List_of_HTTP_header_fields

This error occurs when you start rendering web page stuff before outputting a header. All headers must be completed first.

Check that all echos and prints from php are occurring after session_start() occurs. One tricky place that printing creeps in is when you end php tags and have anything there - even when it's at the end of a page. You don't need ending php tags at the end of your pages and even a space following one will cause this kind of problem. The safest thing is to just remove all ending php tags at the bottom of your php files.

Another tricky thing is that this kind of error is also caused by a "Byte Order Mark" being output by your code editor. You can try opening, fixing and saving the page in just a simple plain-text editor and see if that fixes the problem.