Inherits QPtrCollection.
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.
QCache is a template class. QCache<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 QPtrCollection::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 QPtrCollection::deleteItem() is called. The default implementation deletes the item if auto-deletion is enabled, and does nothing otherwise.
There is a QCacheIterator that can be used to traverse the items in the cache in arbitrary order.
In QCache, 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 QAsciiCache template. A QCache has the same performance as a QAsciiCache.
See also QCacheIterator, QAsciiCache, QIntCache, Collection Classes, and Non-GUI Classes.
size is actually the size of an internal hash array; it's usually best to make it a prime number and at least 50% bigger than the largest expected number of items in the cache.
Each inserted item has an associated cost. When inserting a new item, if the total cost of all items in the cache will exceed maxCost, the cache will start throwing out the older (least recently used) items until there is enough room for the new item to be inserted.
If caseSensitive is TRUE (the default), the cache keys are case sensitive; if it is FALSE, they are case-insensitive. Case-insensitive comparison considers all Unicode letters.
All cache iterators that operate this on cache are reset.
See also remove() and take().
Reimplemented from QPtrCollection.
See also totalCost().
Reimplemented from QPtrCollection.
If there are two or more items with equal keys, the one that was inserted last is returned.
The cache's size is limited, and if the total cost is too high, QCache will remove old, least recently used items until there is room for this new item.
The parameter p is internal and should be left at the default value (0).
Warning: If this function returns FALSE (which could happen, e.g. if the cost of this item alone exceeds maxCost()) you must delete d yourself. Additionally, be very careful about using d after calling this function because any other insertions into the cache, from anywhere in the application or within Qt itself, could cause the object to be discarded from the cache and the pointer to become invalid.
See also setMaxCost() and totalCost().
If there are two or more items with equal keys, the one that was inserted last is returned.
This is the same as find( k, TRUE ).
The item is deleted if auto-deletion has been enabled, i.e., if you have called setAutoDelete(TRUE).
If there are two or more items with equal keys, the one that was inserted last is removed.
All iterators that refer to the removed item are set to point to the next item in the cache's traversal order.
If auto-deleting is turned on, all the items in a collection are deleted when the collection itself is deleted. This is convenient if the collection has the only pointer to the items.
The default setting is FALSE, for safety. If you turn it on, be careful about copying the collection - you might find yourself with two collections deleting the same items.
Note that the auto-delete setting may also affect other functions in subclasses. For example, a subclass that has a remove() function will remove the item from its data structure, and if auto-delete is enabled, will also delete the item.
See also autoDelete().
See also maxCost() and totalCost().
If there are two or more items with equal keys, the one that was inserted last is taken.
All iterators that refer to the taken item are set to point to the next item in the cache's traversal order.
See also remove() and clear().
See also setMaxCost().