问题
All the tutorials say to put session start. They don't say if that should be in all pages on the website, or some, or only 1.
And if it's only 1 page, does it have to be the main page? Or a page with a form that I am making that puts the session ID in the database? If the visitor never visits a page with a session id but they are on the site, do they still have a session id?
回答1:
You need to put this in each page that need to access the session data before accessing (or creating) any session data.
See: http://php.net/manual/en/function.session-start.php
回答2:
Just for a matter of completeness you can choose to write session_start(); in all pages, in just one or in none of them. Let me explain this.
You need to start session in every script where you need access to $_SESSION variable but instead of putting session_start(); in every single script you can create a file headers.php and put there all your repetitive code including session_start();
If everything in your application needs access to $_SESSION you can forget the use of session_start(); simply setting session.auto_start = 1 in your php.ini file. You will be able to access $_SESSION without writing session_start(); before.
More here
回答3:
Anything that is going to access Session variables needs to start the session.
So unless you have a php page that is non-dependent on the session than every page needs it.
回答4:
You need to declare session_start(); in every page if you want to get data from $_SESSION or store data into $_SESSION in those particular page. If you do not need to interact with $_SESSION then you don't have to declare session_start().@hmwhat
来源：https://stackoverflow.com/questions/7129498/write-session-start-on-1-page-or-all-pages