Memcache::add() stores variable var with key only if such key doesn't exist at the server yet. Also you can use memcache_add() function.
The key that will be associated with the item.
The variable to store. Strings and integers are stored as is, other types are stored serialized.
Use MEMCACHE_COMPRESSED to store the item compressed (uses zlib).
Expiration time of the item. If it's equal to zero, the item will never expire. You can also use unix timestamp or a number of seconds starting from current time, but in the latter case the number of seconds may not exceed 2592000 (30 days).
Επιστρέφει TRUE σε επιτυχία ή FALSE σε αποτυχία. Returns FALSE if such key already exist. For the rest Memcache::add() behaves similarly to Memcache::set().