Q3Cache Class Reference
[Qt3Support module]

Detailed Description

The Q3Cache class is a template class that provides a cache based on QString keys.

A cache is a least recently used (LRU) list of cache items. Each cache item has a key and a certain cost. The sum of item costs, totalCost(), never exceeds the maximum cache cost, maxCost(). If inserting a new item would cause the total cost to exceed the maximum cost, the least recently used items in the cache are removed.

Q3Cache is a template class. Q3Cache<X> defines a cache that operates on pointers to X, or X*.

Apart from insert(), by far the most important function is find() (which also exists as operator[]()). This function looks up an item, returns it, and by default marks it as being the most recently used item.

There are also methods to remove() or take() an object from the cache. Calling setAutoDelete(TRUE) for a cache tells it to delete items that are removed. The default is to not delete items when they are removed (i.e., remove() and take() are equivalent).

When inserting an item into the cache, only the pointer is copied, not the item itself. This is called a shallow copy. It is possible to make the cache copy all of the item's data (known as a deep copy) when an item is inserted. insert() calls the virtual function Q3PtrCollection::newItem() for the item to be inserted. Inherit a cache and reimplement newItem() if you want deep copies.

When removing a cache item, the virtual function Q3PtrCollection::deleteItem() is called. The default implementation deletes the item if auto-deletion is enabled, and does nothing otherwise.

There is a Q3CacheIterator that can be used to traverse the items in the cache in arbitrary order.

In Q3Cache, the cache items are accessed via QString keys, which are Unicode strings. If you want to use non-Unicode, plain 8-bit char* keys, use the Q3AsciiCache template. A Q3Cache has the same performance as a Q3AsciiCache.

See also Q3CacheIterator, Q3AsciiCache, and Q3IntCache.

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