Returns FALSE if the key didn't exist in the database.

This will also add the key to the database if it didn't already exist.

The constant SID can also be used to retrieve the current name and session id as a string suitable for adding to URLs. Note that SID is only defined if the client didn't send the right cookie. See also Session handling.

What we didn't say yet is that under the circumstances presented so far, you don't have write access to any zval containers designating function parameters that have been passed to you. Of course, you can change any zval containers that you created within your function, but you mustn't change any zvals that refer to Zend internal data!