Contents

• Public Functions
• Reimplemented Public Functions
• Detailed Description

Detailed Description

TheQ3IntCache class is a template class that provides a cache based on long keys.

Q3IntCache is implemented as a template class. Define a template instanceQ3IntCache<X> to create a cache that operates on pointers to X, or X*.

A cache is a least recently used (LRU) list of cache items, accessed vialong keys. 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 frominsert(), by far the most important function isfind() (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 toremove() ortake() an object from the cache. CallingsetAutoDelete(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() andtake() 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 functionQ3PtrCollection::newItem() for the item to be inserted. Inherit a dictionary and reimplementnewItem() if you want deep copies.

When removing a cache item, the item will be automatically deleted if auto-deletion is enabled.

There is aQ3IntCacheIterator which may be used to traverse the items in the cache in arbitrary order.

Member Function Documentation

Q3IntCache::Q3IntCache(int maxCost = 100,int size = 17)

Constructs a cache whose contents will never have a total cost greater thanmaxCost and which is expected to contain less thansize items.

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 is associated with a cost. When inserting a new item, if the total cost of all items in the cache will exceedmaxCost, the cache will start throwing out the older (least recently used) items until there is enough room for the new item to be inserted.

Q3IntCache::~Q3IntCache()

Removes all items from the cache and then destroys the int cache. If auto-deletion is enabled the cache's items are deleted. All iterators that access this cache will be reset.

[virtual]void Q3IntCache::clear()

Reimplemented fromQ3PtrCollection::clear().

Removes all items from the cache, and deletes them if auto-deletion has been enabled.

All cache iterators that operate this on cache are reset.

See alsoremove() andtake().

[virtual]uint Q3IntCache::count() const

Reimplemented fromQ3PtrCollection::count().

Returns the number of items in the cache.

See alsototalCost().

type * Q3IntCache::find(long k,bool ref = true) const

Returns the item associated withk, or 0 if the key does not exist in the cache. Ifref is TRUE (the default), the item is moved to the front of the least recently used list.

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

bool Q3IntCache::insert(long k, consttype * d,int c = 1,int p = 0)

Inserts the itemd into the cache with keyk and assigns it a cost ofc (default 1). Returns TRUE if it succeeds; otherwise returns FALSE.

The cache's size is limited, and if the total cost is too high,Q3IntCache will remove old, least-used items until there is room for this new item.

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

Warning: If this function returns FALSE (for example, the cost, exceedsmaxCost()), you must deleted yourself. Additionally, be very careful about usingd after calling this function. 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 Q3IntCache::isEmpty() const

Returns TRUE if the cache is empty; otherwise returns FALSE.

int Q3IntCache::maxCost() const

Returns the maximum allowed total cost of the cache.

See alsosetMaxCost() andtotalCost().

bool Q3IntCache::remove(long k)

Removes the item associated withk, and returns TRUE if the item was present in the cache; otherwise returns FALSE.

The item is deleted if auto-deletion has been enabled, i.e. if you have calledsetAutoDelete(TRUE).

If there are two or more items with equal keys, the one that was inserted most recently 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 alsotake() andclear().

void Q3IntCache::setMaxCost(int m)

Sets the maximum allowed total cost of the cache tom. If the current total cost is greater thanm, some items are removed immediately.

See alsomaxCost() andtotalCost().

uint Q3IntCache::size() const

Returns the size of the hash array used to implement the cache. This should be a bit larger thancount() is likely to be.

void Q3IntCache::statistics() const

A debug-only utility function. Prints out cache usage, hit/miss, and distribution information usingqDebug(). This function does nothing in the release library.

type * Q3IntCache::take(long k)

Takes the item associated withk out of the cache without deleting it, and returns a pointer to the item taken out or 0 if the key does not exist in the cache.

If there are two or more items with equal keys, the one that was inserted most recently 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 alsoremove() andclear().

int Q3IntCache::totalCost() const

Returns the total cost of the items in the cache. This is an integer in the range 0 tomaxCost().

See alsosetMaxCost().

type * Q3IntCache::operator[](long k) const

Returns the item associated withk, or 0 ifk does not exist in the cache, and moves the item to the front of the least recently used list.

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

This is the same as find( k, TRUE ).

See alsofind().