QAsciiCache

NAME

SYNOPSIS

Inherits QPtrCollection.

Public Members

DESCRIPTION

QAsciiCache is implemented as a template class. Define a template instance QAsciiCache<X> to create a cache that operates on pointers to X (X*).

A cache is a least recently used (LRU) list of cache items. The cache items are accessed via char* keys. For Unicode keys use the QCache template instead, which uses QString keys. A QCache has the same performace as a QAsciiCache.

Each cache item has a cost. The sum of item costs, totalCost(), will not exceed 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.

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) tells the cache to delete items that are removed. The default is to not delete items when then 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. Its default implementation in QAsciiCache is to delete the item if auto-deletion is enabled.

There is a QAsciiCacheIterator which may be used to traverse the items in the cache in arbitrary order.

See also QAsciiCacheIterator, QCache, QIntCache, Collection Classes, and Non-GUI Classes.  

MEMBER FUNCTION DOCUMENTATION

QAsciiCache::QAsciiCache ( int maxCost = 100, int size = 17, bool caseSensitive = TRUE, bool copyKeys = TRUE )

size is actually the size of an internal hash array; it's usually best to make it prime 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 only affects the 26 letters in US-ASCII. If copyKeys is TRUE (the default), QAsciiCache makes a copy of the cache keys, otherwise it copies just the const char * pointer - slightly faster if you can guarantee that the keys will never change, but very risky.  

QAsciiCache::~QAsciiCache ()

void QAsciiCache::clear () [virtual]

All cache iterators that operate on this cache are reset.

See also remove() and take().

Reimplemented from QPtrCollection.  

uint QAsciiCache::count () const [virtual]

See also totalCost() and size().

Reimplemented from QPtrCollection.  

type * QAsciiCache::find ( const char * k, bool ref = TRUE ) const

If there are two or more items with equal keys, the one that was inserted last is returned.  

bool QAsciiCache::insert ( const char * k, const type * d, int c = 1, int p = 0 )

The cache's size is limited, and if the total cost is too high, QAsciiCache will remove old, least recently used items until there is room for this new item.

Items with duplicate keys can be inserted.

The parameter p is internal and should be left at the default value (0).

Warning: If this function returns FALSE, 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.  

bool QAsciiCache::isEmpty () const

int QAsciiCache::maxCost () const

See also setMaxCost() and totalCost().  

type * QAsciiCache::operator[] ( const char * k ) const

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 ).

See also find().  

bool QAsciiCache::remove ( const char * k )

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.

See also take() and clear().  

void QAsciiCache::setMaxCost ( int m )

See also maxCost() and totalCost().  

uint QAsciiCache::size () const

void QAsciiCache::statistics () const

type * QAsciiCache::take ( const char * k )

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().  

int QAsciiCache::totalCost () const

See also setMaxCost().

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